DESCRIPTION Title of Invention: Hot Stamped High Strength Part Excellent in Post painting anticorrosion property and 5 Method of Production of Same Technical Field [OOOl] The present invention relates to an aluminum plated high strength part which is excellent in post 10 painting anticorrosion property which is produced by press forming at a high temperature, that is, by hot stamping, and is suitable for members in which strength is required such as auto parts and other structural members, more specifically relates to a high strength 15 part which is formed by hot stamping which is suppressed in propagation of cracks which form in the aluminum plating layer when hot stamping aluminum plated high strength steel sheet and which is excellent in post painting anticorrosion property, and a method of 20 production of the same. Background Art [0002] In recent years, in applications of steel sheet for automobile use (for example, automobile pillars, door impact beams, bumper beams, etc.) and the like, steel sheet in which both high strength and high formability are achieved has been desired. As one means for dealing with this, there is TRIP (transformation induced plasticity) steel which utilizes the martensite transformation of residual austenite. Using this TRIP steel, it is possible to produce high strength steel sheet which is excellent in formability and which has a 1000 MPa class or so strength, but securing formability with very high strength steel sheet of further higher strength, for example, 1500 MPa or more, has been difficult. [ 0 0 0 3 ] In view of this situation, the forming method which has been focused on most recently as a method for securing high strength and high formability has been hot stamping (also called hot pressing, hot stamping, die quenching, press quenching, etc.) This hot stamping heats the steel sheet to the 800°C or higher austenite region, then forms it by a die when hot to thereby improve the formability of the high strength steel sheet and, after forming it, cools it in the press die to quench it and thereby obtain a shaped part of the desired quality. [ 0 0 0 4 ] Hot stamping is promising as a method for forming very high strength members, but usually includes a step of heating the steel sheet in the atmosphere. At this time, oxides (scale) form on the steel sheet surface, so a later step of removing the scale becomes necessary. In this regard, in such a later step, there was the problem of the need for measures from the viewpoint of the descaling ability and environmental load etc. [OOOS] As art to alleviate this problem, the art of using aluminum plated steel sheet as the steel sheet for hot stamped member use so as to suppress the formation of scale at the time of heating has been proposed (for example, see PLTs 1 and 2) . [0006] Aluminum plated steel sheet is effective for the efficient production of a high strength shaped part by hot stamping. Aluminum plated steel sheet is usually pressed formed, then painted. The aluminum plating layer after heating at the time of hot stamping changes to an intermetallic compound up to the surface. This compound is extremely brittle. If subjected to a severe forming operation by hot stamping, the aluminum plating layer easily cracks. Further, the phases of this intermetallic compound have more electropositive potential than the matrix steel sheet, so there was the problem that the corrosion of the steel sheet material is started from the cracks as starting points and the post painting anticorrosion property falls. [0007] To avoid the drop in the post painting anticorrosion property due to the formation of cracks in the aluminum plating layer, adding Mn to this intermetallic compound is extremely effective, so an aluminum plated steel sheet which is improved in post painting anticorrosion property by addition of 0.1% or more of Mn in the aluminum plating layer has been proposed (for example, see PLT 3) . [ 0 0 0 8 ] The art which is described in PLT 3 adds specific ingredient elements in the aluminum plating layer to prevent cracks from forming in the aluminum plating layer, but is not art which prevents cracks from forming in the aluminum plating layer without addition of specific ingredient elements into the aluminum plating layer. [ 0 0 0 9 ] Further, aluminum plated steel sheet has been proposed where, if adding elements to the matrix steel of the aluminum plated steel sheet to give Ti+O.lMn+O.lSi+O.lCr>0.25, these elements promote diffusion between A1-Fe so that even if cracks are formed in the aluminum plating layer, an Fe-A1 reaction proceeds from around them and therefore the steel sheet material is prevented from being exposed and the corrosion resistance is improved (for example, see PLT 4). [ 0 0 10 ] However, the art which is described in PLT 4 does not try to prevent cracks from forming at the aluminum plating layer. Citations List Patent Literature [ 0011 ] PLT 1: Japanese Patent Publication No. 2003- 181549A PLT 2: Japanese Patent Publication No. 2003-49256A PLT 3: Japanese Patent Publication No. 2003-34855A PLT 4: Japanese Patent Publication No. 2003-34846A Summary of Invention Technical Problem [0012] The present invention was made in consideration of this situation and has as its object the provision of a hot stamped high strength part in which the propagation of cracks which form at the aluminum plating layer when hot stamping aluminum plated steel sheet is suppressed and the post painting anticorrosion property is excellent even without adding special ingredient elements which suppress formation of cracks in an aluminum plating layer. Further, it has as its object the formation of a lubricating film at the aluminum plating layer surface to improve the formability at the time of hot stamping aluminum plated steel sheet and suppress the formation of cracks in the aluminum plating layer. Furthermore, it has as its object the provision of a method of production of a hot stamped high strength part. Solution to Problem [0013] The inventors engaged in intensive research to solve the above problems and completed the present invention. In general, an aluminum plated steel sheet for hot stamped member use is formed with an aluminum plating layer at one or both surfaces of the steel sheet by hot dipping etc. The aluminum plating layer may contain, by mass%, Si: 2 to 7% in accordance with need and is comprised of a balance of A1 and unavoidable impurities. [ 0 0 14 1 When an aluminum plating layer of aluminum plated steel sheet before hot stamping contains Si, it is comprised of an A1-Si layer and Fe-Al-Si layer from the surface layer. To hot stamp an aluminum plated steel sheet, first, the aluminum plated steel sheet is heated to a high temperature to make the steel sheet an austenite phase. Further, the aluminum plated steel sheet which is converted to austenite is press formed hot, then the shaped aluminum plated steel sheet is cooled. The aluminum plated steel sheet can be made a high temperature to make it soften once and facilitate the subsequent press forming. Further, the steel sheet may be heated and cooled so that it is quenched and an approximately 1500 MPa or higher mechanical strength is realized. [0015] In the heating step of this aluminum plated steel sheet for hot stamped member use, inside the aluminum plating layer (when including Si), the A1-Si and the Fe from the steel sheet mutually diffuse thereby changing as a whole to an A1-Fe compound (intermetallic compound). At this time, in the A1-Fe compound, a phase which contains Si also is partially formed. This compound (intermetallic compound) is extremely brittle. If shaping it under severe conditions in hot stamping, cracks will form in the aluminum plating layer. Further, these phases have a potential more electropositive than the matrix steel sheet, so corrosion of the steel sheet material will begin from the cracks as starting points and the shaped part will be reduced in post painting anticorrosion property. Therefore, suppression of the cracks which form in the aluminum plating layer after hot stamping improves the post painting anticorrosion property of the part which is formed by hot stamping. [0016] In hot stamping, it is not possible to avoid the formation of cracks in the aluminum plating layer, but the inventors took note of the fact that if it were possible to arrest the propagation of cracks of the aluminum plating layer which formed in hot stamping inside of the aluminum plating layer, the cracks would not reach the matrix steel sheet. They discovered that this would enable prevention of corrosion of the steel sheet material and prevention of a detrimental effect on the post painting anticorrosion property of the hot stamped part. The inventors engaged in intensive research on arresting the propagation of cracks of an aluminum plating layer for cracks which formed in the aluminum plating layer. As a result, they discovered that if controlling the mean linear intercept length of crystal grains of an intermetallic compound phase which contains A1 in 40 to 65% among the crystal grains of the plurality of intermetallic compound phases based on A1-Fe which are formed at the surface of the steel sheet (below, sometimes simply referred to as the "mean linear intercept length") to 3 to 20 p , it is possible to arrest the propagation of cracks which form in the aluminum plating layer. Further, they discovered that by further forming a lubrication film which contains ZnO at the aluminum plating layer surface, it is possible to secure a lubricating property at the time of hot stamping and possible to prevent surface defects and formation of cracks. Furthermore, they discovered a steel sheet composition which is suitable for hot stamping. [ 0 0 17 1 Furthermore, the inventors discovered that the thickness of the A1-Fe alloy plating layer has an effect on the state of spattering at the time of spot welding and discovered that to obtain stable spot weldability, it is important reduce the deviation of the plating thickness (standard deviation), make the average value of thickness of the A1-Fe alloy plating layer 10 to 50 p , and make the ratio of the average value of thickness to the standard deviation of thickness (standard deviation of thickness/average value of thickness) 0.15 or less. [ 0 0 18 ] The present invention was completed based on these discoveries and has as its gist the following: [0019] (1) A hot stamped high strength part which is excellent in post painting anticorrosion property, comprising an alloy plating layer comprising an A1-Fe intermetallic compound phase on the surface of the steel sheet, the alloy plating layer is comprised from phases of a plurality of intermetallic compounds, a mean linear intercept length of crystal grains of a phase containing Al: 40 to 65 mass% among the phases of the plurality of intermetallic compounds is 3 to 20 p , an average value of thickness of the A1-Fe alloy plating layer is 10 to 50 pm, and a ratio of the average value of thickness to the standard deviation of thickness of the A1-Fe alloy plating layer satisfies the following relationship: O a-phase -> FeA13 phase -> Fe2A15 phase. By going through the transformations, crystal grains are formed again, so the greater the transformations which are gone through, the smaller the mean linear intercept length tends to become. That is, the mean linear intercept length becomes smaller with the a-phase than the FeA13 phase and with the P-phase than the a-phase. [0045] The method of measurement of a mean linear intercept length in an alloy plating layer is to polish any cross-section of a hot stamped part, then etch it by 2 to 3 vo1% of Nital and examine the result by a microscope. For the examination, a polarization microscope is used. The polarization angle is adjusted so that the contrast of the crystal grains becomes the clearest. At this time, the layer of a compound whose contrast appears light at the surface layer side consecutively from the layer of a compound whose contrast appears dark is a phase of Al: 40 to 65%. This phase is a phase which has the property of arresting the crack propagation and is a phase which affects the post painting anticorrosion property and the plating workability. As shown in FIGS. 3 (a) to (b) , in particular when the plating thickness is thin (40 g/m2 per side), due to the effect of the dark contrast phase, the mean linear intercept length of Al: 40 to 65% phase is difficult to measure. Therefore, in this Description, the mean linear intercept length of the crystal grains in the alloy plating layer is defined as the mean linear intercept length which is measured in the direction parallel to the steel sheet surface. The mean linear intercept length is found by the line segment method. As shown in FIG. 3(a), the mean linear intercept length is found by drawing a line parallel to the steel sheet surface in the plating layer, counting the number of grain boundaries which this line passes through, and dividing the measured length by the number of grain boundaries. It is possible to calculate the grain size from this mean linear intercept length, but calculation of the grain size requires that the shape of the grains be known. In steel sheet, crystal grains can be assumed to be spherical, but the intermetallic compounds which are formed at the surface like in the present invention are unknown in crystal grain shape, so the mean linear intercept length was used. [0046] Note that, in actual measurement, in the polarization micrographs of FIGS. 3(a) to (d), the grain boundaries are unclear, so as shown in FIGS. 5(a) and (b), the crystal grain boundaries were traced in the polarization micrographs of FIGS. 3(a) and (c) to clarify the crystal grain boundaries. [0047] The reason for limiting the mean linear intercept length of a phase which contains Al: 40 to 65% after the aluminum plating layer is alloyed to 3 to 20 p will be explained. A small grain size is preferable as a crack propagation arrest property of a phase which contains Al: 40 to 65%, but the steel sheet for hot stamping member use has to be heated once to the austenite region. For this reason, this steel sheet is generally heated to 850°C or more, so the aluminum plating layer which is alloyed in this heating step ends up with crystal grains growing to 3 p or more. Therefore, usually making the crystal grain size less than 3 pm is extremely difficult. If the mean linear intercept length exceeds 20 p and the grain size becomes larger, the aluminum plating layer falls in workability and the phenomenon of powdering becomes greater. Furthermore, the crack propagation arrest property of a phase which contains Al: 40 to 65% no longer functions and cracks can no longer be arrested by the crystal grains. [ 0 0 4 8 ] Therefore, in the present invention, the mean linear intercept length of a phase which contains Al: 40 to 65% was limited to 3 to 20 p , preferably it is 5 to 17 pm. [0049] Next, the effects of the aluminum plating conditions and heating conditions at the time of hot stamping on the mean linear intercept length will be explained. [OOSO] FIG. 4 is a view which shows the effects of the aluminum plating conditions and the heating conditions at the time of hot stamping on the mean linear intercept length. In FIG. 4, the abscissa shows the Larson-Miller parameter (LMP) of the heating conditions at the time of hot stamping. The Larson-Miller parameter (LMP) is expressed by LMP=T (20+logt) (wherein, T: absolute temperature (K), t: time (hrs)). Here, T is the heating temperature of the steel sheet, while "t" is the holding time in the heating furnace after reaching the target temperature. LMP is an indicator which is used in general for treating the temperature and time in a unified manner in heat treatment and phenomena such as creep where the temperature and time have an effect. This parameter can also be used for the growth of crystal grains. In the present invention, LMP summarizes the effects of temperature and time on the mean linear intercept length of crystal grains, so the heat treatment conditions at the time of hot stamping can be described by just this parameter. [OOSl] The symbols which are described in FIG. 4 will be explained. A and B show aluminum plating conditions. A means a 7% Si bath of a bath temperature of 660°C, while B means a 11% Si bath of a bath temperature of 640°C. These are typical conditions whereby an a-AlFeSi phase and a PAlFeSi phase are produced at the time of aluminum plating. Further, "5°C/s" and "50°C/s" mean the temperature elevation rates at the time of hot stamping. 5OC/s corresponds to usual furnace heating, while 50°C/s corresponds to infrared heating, ohmic heating, and other rapid heating. Here, the "temperature elevation rate" means the average temperature elevation rate from the start of temperature elevation to a temperature 10°C lower than the target temperature. If comparing the aluminum plating conditions A and B, the trend is that forming an a-AlFeSi phase at the time of the conditions A, that is, aluminum plating, gives a mean linear intercept length greater than the conditions B. It was learned that it is necessary to limit the range of heating conditions at the time of hot stamping to a narrower range (LMP=20000 to 23000). If the LMP is less than 20000, the diffusion of the A1-Si plating layer with the steel sheet is insufficient and an unalloyed A1-Si layer remains, so this is not preferred. Further, in the plating conditions A of FIG. 4, comparing the temperature elevation rates of 5OC/sec and 50°C/sec, it is shown that even with such a narrow range, if increasing the temperature elevation rate at the hot stamping, the structure becomes finer. The temperature elevation rate is preferably 4 to 200°C/sec(s) in range. If the temperature elevation rate is slower than 4OC/sec, this means that the heating step takes time and means that the hot stamping falls in productivity. Further, if faster than 200°C/sec, control of the temperature distribution in the steel sheet becomes difficult. Both are not preferred. Establishing suitable aluminum plating conditions and hot stamping conditions enables the mean linear intercept length to be made 3 to 20 pm. [0052] As explained above, by making the mean linear intercept length of the crystal grains of a phase containing Al: 40 to 65% in the layer of the intermetallic compounds mainly comprised of A1-Fe which is formed at the surface of the steel 3 to 20 p, it is possible to arrest the propagation of cracks which form at the plating layer due to hot stamping inside the plating layer. Due to this, it is possible to suppress corrosion of the steel sheet matrix due to cracks in the plating layer and possible to obtain high strength auto parts which are excellent in post painting anticorrosion property and other hot stamped parts. [0053] The hot stamped high strength parts of the present invention further may have a surface film which contains ZnO at the surface of the alloy plating layer mainly comprised of A1-Fe. 100541 The hot stamped high strength part of the present invention has the extremely hard A1-Fe intermetallic compounds formed at the plating layer of the steel sheet surface at the time of hot stamping. For this reason, working defects are formed at the surface of the shaped part due to contact with the die at the time of press forming in the hot stamping. There is the problem that these working defects because the cause of cracks in the plating layer. The inventors discovered that by forming a surface film which has excellent lubricity at the surface of the aluminum plating layer, it is possible to suppress the working defects of a shaped part and the occurrence of cracks in the plating layer and discovered that it is possible to improve the formability at the time of hot stamping and the corrosion resistance of a shaped part. [0055] The inventors engaged in intensive studies on a surface film which has lubricity which is suitable for hot stamping and as a result discovered that providing the surface of the aluminum plating layer with a lubricating surface film layer which contains ZnO (zinc oxide), it is possible to effectively prevent working defects of the shaped part surface and cracks in the plating layer. [0056] ZnO is included in the surface film layer at one side of the aluminum plated steel sheet in an amount, converted to mass of Zn, of 0.3 to 7 g/m2. More preferably, it included in 0.5 to 4 g/m2. If the content of ZnO is, converted to mass of Zn, 0.1 g/m2 or more, the effect of improvement of the lubricity and effect of prevention of segregation (effect of enabling uniform thickness of aluminum plating layer) etc. can be effectively exhibited. On the other hand, when the content of ZnO exceeds, converted to mass of Zn, 7 g/m2, the total thickness of the aluminum plating layer and surface film layer becomes too thick and the weldability or painting adhesion falls. [0057] FIG. 6 is a view which shows the relationship between the amount of deposition of Zn on the aluminum plated steel sheet surface and the coefficient of dynamic friction. The content of ZnO in the surface film layer was changed to evaluate the lubricity at the time of hot stamping. This lubricity was evaluated by the following test. First, different test materials of the aluminum plated steel sheet which has an ZnO film layer (150x200 mrn) were heated to 900°C, then were cooled down to 700°C. The test materials were subjected to loads from above through steel balls. Further, the steel balls were slid out over the test materials. At this time, the pullout load was measured by a load cell. The ratio of the pullout load/push-in load was made the coefficient of dynamic friction. The results are shown in FIG. 6. If the coefficient of dynamic friction is smaller than 0.65, it is evaluated as good. It is learned that in a region where the amount of deposition of Zn is generally 0.7 g/m2 or more, the coefficient of dynamic friction is effectively kept low and the hot lubricity can be improved. [0058] A surface film layer which contains ZnO can be formed, for example, by applying a paint which contains ZnO and baking or drying it after applying for curing so as to enable formation over the aluminum plating layer. As the method of applying a ZnO paint, for example, the method of mixing a predetermined organic binder and a dispersion of ZnO powder and applying it to the surface of the aluminum plating layer, a method of painting by powder painting, etc. may be mentioned. As the method of baking and drying after applying, for example, a hot air furnace, induction heating furnace, near infrared ray furnace, or other method or a method combining the same may be mentioned. At this time, depending on the type of the binder which is used for applying, instead of baking and drying after applying, for example, curing by ultraviolet rays or electron beams etc. is possible. As the predetermined organic binder, for example, a polyurethane resin or polyester resin etc. may be mentioned. However, the method of forming the ZnO surface film layer is not limited to these examples and can be formed by various methods. [0059] Such a surface film layer which contains ZnO can improve the lubricity of an aluminum plated steel sheet at the time of hot stamping, so working defects of the plating layer and cracks in the plating layer at the surface of the shaped part can be suppressed. [0060] ZnO has a melting point of approximately 1975°C or higher compared with the aluminum plating layer (the melting point of aluminum is approximately 660°C) etc. Therefore, even when working steel sheet at for example 800°C or more such as when working a coated steel sheet by the hot stamping method etc., the surface film layer which contains this ZnO will not melt. Therefore, even if heating of the aluminum plated steel sheet causes the aluminum plating layer to melt, the state where the ZnO surface film layer covers the aluminum plating layer to be maintained, so it is possible to prevent the thickness of the melted aluminum plating layer from becoming uneven. Note that, uneven thickness of the aluminum plating layer of a hot stamped high strength part easily occurs, for example, in the case of heating by a furnace where the blank is oriented vertically with respect to the direction of gravity or the case of heating by ohmic heating or induction heating. However, this surface film layer can prevent uneven thickness of the aluminum plating layer when such heating is performed and enables aluminum plating layer to be formed thicker. [0061] In this way, an ZnO surface film layer exhibits the effects of improving the lubricity and making the thickness of the aluminum plating layer uniform etc. so can improve the formability at the time of press forming in hot stamping and the corrosion resistance after press forming . Further, the aluminum plating layer can be made uniform in thickness, so can be rapidly heated by ohmic heating or induction heating enabling a higher temperature elevation rate. This is effective for making the mean linear intercept length of the crystal grains of an intermetallic compound phase which contains Al: 40 to 6 5mass% 3 to 20 pm. [0062] Furthermore, this ZnO surface film layer never causes a drop in the spot weldability, paint adhesion, post painting anticorrosion property, and other performance. The post painting anticorrosion property is rather further improved by imparting a surface film layer. [0063] Next, the inventors studied the composition of ingredients for steel sheet for obtaining the aluminum plated steel sheet for rapidly heated hot stamped member use provided with both excellent corrosion resistance and excellent productivity. As a result, since the hot stamping was performed with the pressing and quenching simultaneously by the die, they obtained the ingredients for the steel sheet which are explained below from the viewpoint of the aluminum plated steel sheet for hot stamped member use containing ingredients enabling easy quenching and thereby giving hot stamped parts which have a 1000 MPa or more high strength after hot stamping. [0064] Below, the reasons for limiting the ingredients of the steel sheet in the present invention will be explained. Note that, the % of the ingredients mean mass%. [0065] C: 0.1 to 0.5% The present invention provides a hot stamped part which has a 1000 MPa or more high strength after shaping. To obtain high strength, the steel has to be rapidly cooled after hot stamping to transform it to a structure of mainly martensite. From the viewpoint of improvement of the hardenability, an amount of C of at least 0.1% is necessary. On the other hand, if the amount of C is too great, the toughness of the steel sheet remarkably falls, so the workability falls. For this reason, the amount of C is preferably 0.5% or less. 100661 Si: 0.01 to 0.7% Si promotes a reaction between the A1 and Fe in the plating and has the effect of raising the heat resistance of the aluminum plated steel sheet. However, Si forms a stable oxide film during the recrystallization annealing of the cold rolled steel sheet at the steel sheet surface, so is an element which obstructs the properties of the aluminum plating. From this viewpoint, the upper limit of the amount of Si is made 0.7%. However, if making the amount of S less than 0.01%, the fatigue property deteriorates, so this is not preferable. Therefore, the amount of Si is 0.01 to 0.7%. [0067] Mn: 0.2 to 2.5% Mn is well known as an element which raises the hardenability of steel sheet. Further, it is also an element which is necessary for preventing hot embrittlement due to the unavoidably entering S. For this reason, 0.2% or more has to be added. Further, Mn raises the heat resistance of steel sheet after aluminum plating. However, if over 2.5% of Mn is added, the part which is hot stamped after quenching falls in impact properties, so 2.5% is made the upper limit. [0068] Al: 0.01 to 0.5% A1 is suitable as a deoxidizing element, so 0.01% or more may be included. However, if included in a large amount, coarse oxides are formed and the mechanical properties of the steel sheet are impaired, so the upper limit of the amount of A1 is made 0.5%. [0069] P: 0.001 to 0.1% P is an impurity element which is unavoidably included in steel sheet. However, P is a solution strengthening element. It can raise the strength of the steel sheet relatively inexpensively, so the lower limit of the amount of P was made 0.001%. However, if recklessly increasing the amount of addition, the toughness of the high strength material is lowered and other detrimental effects appear, so the lower limit of the amount of P was made 0.1%. [ 0 0 7 0 ] S: 0.001 to 0.1% S is an unavoidably included element. It forms inclusions of MnS in the steel. If the MnS is large in amount, the MnS forms starting points of fracture, obstructs ductility and toughness, and becomes a cause of deterioration of workability. Therefore, the amount of S is preferably as low as possible. The upper limit of the amount of S was made 0.1% or less, but reducing the amount of S more than necessary is not preferable from the viewpoint of manufacturing costs, so the lower limit was made 0.001%. [0071] N: 0.0010% to 0.05% N easily bonds with Ti or B, so has to be controlled so as not to decrease the effects targeted by these elements. An amount of N of 0.05% or less is allowable. Preferably, the amount of N is 0.01% or less. On the other hand, reduction more than necessary places a massive load on the steelmaking step, so 0.0010% should be made the target for the lower limit of the amount of N. [0072] Next, the ingredients which can be selectively contained in the steel will be explained. [0073] Cr: over 0.4% to 3% Cr is also an element which generally raises the hardenability. It is used in the same way as Mn, but also has a separate effect when applying an aluminum plating layer to steel sheet. If Cr is present, for example, when box annealing the steel after applying the aluminum plating layer so as to alloy the aluminum plating layer, the plating layer and the steel sheet matrix easily alloy with each other. When box annealing the aluminum plated steel sheet, A1N is formed in the aluminum plating layer. A1N suppresses the alloying of the aluminum plating layer and leads to peeling of the plating, but addition of Cr makes formation of A1N difficult and makes alloying of the aluminum plating layer easier. To obtain these effects, the amount of Cr is over 0.4%. However, even if adding Cr in an amount of over 3%, the effect becomes saturated. Further, the cost also rises. In addition, the aluminum plating property falls. Therefore, the upper limit of the amount of Cr is 3%. [0074] Mo: 0.005 to 0.5% Mo, like Cr, has the effect of suppressing the formation of AlN, which causes peeling of the plating layer, formed at the interface of the plating layer and the steel sheet matrix when box annealing the aluminum plating layer. Further, it is a useful element from the viewpoint of the hardenability of the steel sheet. To obtain these effects, an amount of Mo of 0.005% is necessary. However, even if adding over 0.5%, the effect becomes saturated, so the upper limit of the amount of Mo is 0.5%. [0075] B: 0.0001 to 0.01% B also is a useful element from the viewpoint of the hardenability of steel sheet and exhibits its effect at 0.0001% or more. However, even if adding over 0.01%, the effect becomes saturated and, further, casting defects and cracking of the steel sheet at the time of hot rolling occur etc. and the manufacturability otherwise drops, so the upper limit of the amount of B is 0.01%. Preferably, the amount of B is 0.0003 to 0.005%. [0076] W: 0.01to 3% W is a useful element from the viewpoint of the hardenability of steel sheet and exhibits its effect at 0.01% or more. However, even if over 3% is added, the effect becomes saturated and, further, the cost also rises, so the upper limit of the amount of W is 3%. [0077] V: 0.01 to 2% V, like W, is a useful element from the viewpoint of the hardenability of steel sheet and exhibits its effect at 0.01% or more. However, even if V us added in an amount over 3%, the effect becomes saturated and, further, the cost also rises, so the upper limit of the amount of V is 2%. [ 0 0 7 8 ] Ti: 0.005 to 0.5% Ti can be added from the viewpoint of fixing the N. By mass%, Ti has to be added in an amount of approximately 3.4 times the amount of N, but N, even if decreased, is present in 10 ppm or so, so the lower limit of the amount of Ti was made 0.005%. Further, even if excessively adding Ti, the hardenability of the steel sheet is caused to fall or the strength is also caused to fall, so the upper limit of the amount of Ti is 0.5%. [0079] Nb: 0.01 to 1% Nb, like Ti, can be added from the viewpoint of fixing the N. By mass%, Nb has to be added in an amount of approximately 6.6 times the amount of N, but N, even if decreased, is present in 10 ppm or so, so the lower limit of the amount of Nb was made 0.01%. Further, even if excessively adding Nb, the hardenability of the steel sheet is caused to fall or the strength is also caused to fall, so the upper limit of the amount of Nb is 18, preferably 0.5%. [ 0 0 8 0 1 Further, as ingredients in a steel sheet, even if Ni, Cu, Sn, Sb, are further included, the effect of the present invention is not obstructed. Ni is a useful element from the viewpoint of not only the hardenability of steel sheet, but also the low temperature toughness which in turn leads to improvement of the impact resistance. It exhibits this effect at 0.01% or more of Ni. However, even if adding Ni in over 5%, the effect becomes saturated and the cost rises, so N may be added in the range of 0.01 to 5%. Cu is also a useful element from the viewpoint of not only the hardenability of steel sheet, but also the toughness. It exhibits this effect at 0.1% or more of Cu. However, even if adding Cu in over 3%, the effect becomes saturated and the cost rises. Not only that, deterioration of the slab properties and cracks and defects in the steel sheet at the time of hot rolling are caused, so Cu should be added in 0.01 to 3% in range. Furthermore, Sn and Sb are both elements which are effective for improving the wettability and bondability of the plating with respect to the steel sheet. An amount of 0.005% to 0.1% can be added. If both are amounts of less than 0.005%, no effect can be recognized, while if over 0.1% is added, defects easily are caused at the time of production and, further, a drop in toughness is caused, so the upper limits of the amount of Sn and the amount of Sb are 0.1%. [ 0 0 8 1 ] Further, the other ingredients are not particularly prescribed. Sometimes Zr, As, and other elements enter from the iron scrap, but if in the usual range, they do not affect the properties of the steel which is used for the present invention. [0082] Next, the method of production of a hot stamped high strength part will be explained. [0083] The aluminum plated steel sheet for hot stamped member use which is used in the present invention is produced by taking cold rolled steel sheet which has been obtained by hot rolling steel, then cold rolling it, and plating it on a hot dipping line with an annealing temperature of 670 to 760°C and a furnace time in the reducing furnace of 60 sec or less to treat the steel sheet with aluminum plating which contains Si: 7 to 15%. It is effective to make the skin pass rolling rate after aluminum plating 0.1 to 0.5%. 100841 The annealing temperature of the hot dipping line has an effect on the shape of the steel sheet. If the annealing temperature is raised, the steel sheet easily warps in the C direction. As a result, at the time of aluminum plating, the difference in plating coating deposition amounts at the center part of the steel sheet in the width direction and near the edges will easily become larger. From this viewpoint, the annealing temperature is preferably 760°C or less. Further, if the annealing temperature is too low, the temperature of the sheet when being dipped in the aluminum plating bath falls too much and dross defects easily are caused, so the lower limit of the annealing temperature is 670°C. [0085] The furnace time in the reducing furnace affects the aluminum plating properties. Si, Cr, Al, and other elements which oxidize more easily than Fe easily oxidize in the reducing furnace at the steel sheet surface and obstruct the reaction between the aluminum plating bath and the steel sheet. In particular, if the furnace time in the reducing furnace is long, this effect becomes remarkable, so the furnace time is preferably 60 sec or less. Note that the lower limit of the furnace time is not particularly defined, but 30 sec or more is preferable. [0086] After the aluminum plating, for shape adjustment etc., the sheet is rolled by skin pass rolling, but the rolling rate at this time affects the alloying of the aluminum plating layer at the time of hot stamping. Due to the rolling, strain is introduced into the steel sheet and plating layer. This is believed to be a result of this. If the rolling rate is high, the alloy layer after hot stamping tends to become smaller in crystal grain size, but it is not preferable if the rolling rate is made too low since the alloy layer which is produced is given cracks. For this reason, the rolling rate is preferably made 0.1 to 0.5%. [ 0 0 8 7 ] Further, after the aluminum plating, box annealing can be performed to make the aluminum plating layer alloyed. At this time, to promote the alloying, the steel preferably is made to include Cr, Mo, etc. The box annealing is for example performed at 650°C for 10 hours or SO. [ 0 0 8 8 ] The thus obtained aluminum plated steel sheet can be rapidly heated in the subsequent hot stamping step by a 50°C/sec or more temperature elevation rate. Further, rapid heating is effective for making the mean linear intercept length of the crystal grains in a phase containing Al: 40 to 65% in the A1-Fe alloy layer 3 to 20 pm. The heating system is not particularly limited. The usual furnace heating or an infrared type of heating system using radiant heat may be used. Further, it is also possible to use ohmic heating or high frequency induction heating or another heating system using electricity which enables rapid heating by a temperature elevation rate of 50°C/sec or more. [0089] The upper limit of the temperature elevation rate is not particularly defined, but when using the above ohmic heating or high frequency induction heating or other heating system, due to the performance of the systems, 300°C/sec or so becomes the upper limit. [0090] Further, at this heating step, the peak sheet temperature is preferably made 850°C or more. The peak sheet temperature is made 850°C or more so as to heat the steel sheet to the austenite region and promote sufficient alloying of the aluminum plating layer up to the surface. [009l] Next, the aluminum plated steel sheet in the heated state is hot stamped to a predetermined shape between a pair of top and bottom forming dies. After being formed, it is held stationary at the press bottom dead center for several seconds to quench it by cooling by contact with the forming dies and thereby obtain the hot stamped high strength part of the present invention. [0092] The hot stamped part was welded, chemically converted, painted by electrodeposition, etc. to obtain the final product. Usually, cationic electrodeposition painting is used. The film thickness becomes 1 to 30 pn or so. After the electrodeposition painting, an intermediate painting, top painting, and other painting are sometimes also applied. Examples [0093] Below, examples will be used to explain the present invention in further detail. Example 1 After the usual hot rolling step and cold rolling step, a cold rolled steel sheet of the steel ingredients such as shown in Table 1 (sheet thickness 1.4 mrn) was covered by hot dip aluminum plating containing Si. For the hot dip aluminum plating, a nonoxidizing furnace-reducing furnace type of line was used. After the plating, gas wiping was used to adjust the plating coating deposition amount to a total for the two sides of 160 g/m2, then the sheet was cooled. At this time, as the plating bath composition, there were (A) : A1-7%Si-2%Fe, bath temperature 660°C, and (B) : Al-11%Si-2%Fe, bath temperature 640°C. The plating bath conditions correspond to the phases at the aluminum plating conditions A and B of FIG. 4. It should be noted that the Fe in the bath is unavoidable Fe which is supplied from the plating equipment and strips in the bath. Further, the annealing temperature was made 720°C and the furnace time in the reducing furnace was made 45 sec. The aluminum plated steel sheet was generally good in appearance with no nonplating defects etc. [0094] The thus prepared test piece was evaluated for post painting anticorrosion property. The hot stamping was performed using a usual furnace heating means. The temperature elevation rate of the aluminum plated steel sheet was approximately 5'C/sec. A 250x300 mrn large test piece was heated in the air. The piece was elevated in temperature over approximately 3 minutes, then was held for approximately 1 minute, then removed from the furnace and cooled down to approximately 700°C in temperature, formed into a hat shape, and cooled in the die. At this time, the cooling rate was approximately 200°C/sec. As shown in Table 2, the heating temperature of the test piece was changed in various ways to control the structure of the aluminum plating layer after alloying. [0095] The vertical wall part of the hat shaped part was cut out to 50x100 mm and evaluated for post painting anticorrosion property. The chemical conversion solution PB-SX35 made by Parkerizing used for chemical conversion, then the cationic electrodeposition paint Powernix 110 made by Nippon Paint was painted to give an approximately 20 pm thickness. After that, a cutter was used to crosscut this film, then a composite corrosion test defined by the Society of Automobile Engineers of Japan (JASO M610- 92) was performed for 180 cycles (60 days). The extent of blistering from a cross-cut (maximum blistering at the cross-cut (maximum blister width at one side) was measured. At this time, the blister width of general rust-proof steel sheet, that is, GA (hot dip galvannealed steel sheet) (amount of deposition of 45 g/m2 at one side) was 5 mm. [0096] The post painting anticorrosion property was evaluated as "very good" with a blister width of 4 mm or less, as "good" with a blister width of over 4 mm to 6 mm, and as "poor" with a blister width of over 6 mm. [0097] Regarding evaluation of the spot weldability, this has to be performed by a flat sheet, so a 400x500 mm plate shaped die was used. The usual furnace heating means was used, 400x500 mm aluminum plated steel sheet was heated by a temperature elevation rate of approximately 5OC/sec in the air, the sheet was evaluated in temperature over approximately 3 minutes, then was held for approximately 1 minute, then was taken out of the furnace, cooled in the air down to approximately 700°C in temperature, then quenched in the die. 30 mm of the two edges of the aluminum plated steel sheet, plated by A1 on a hot dipping line, in the width direction were cut off. The rest was used for the tests. After hot stamping, the part was quenched, then a 30x50 mm weld test piece was cut out and measured for suitable weld current range by a pressure of 500 kgf and electrification for 10 cycles (60Hz). At this time, the lower limit current was made 4dt ("t" is the sheet thickness), while the upper limit current was made the spattering. The upper limit current value - lower current value was made the suitable weld current range. [0098] The spot weldability was evaluated as "good" when over the suitable weld current range 2 kA and "poor" when the suitable weld current range 2 kA or less. [0099] Further, after Nital etching, the test piece was examined in cross-section and the average value of thickness, the standard deviation of thickness (deviation in plating thickness), and the ratio of the average value of thickness to the standard deviation of thickness (standard deviation/average) were found for the plating thickness. Further, the alloy layer structure was examined and the mean linear intercept length of the crystal grains of a phase which contains Al: 40 to 65 mass% was measured. At this time, the test piece was cut out from the flange part with little deformation at the hat shaped part. [ 0 10 0 ] Note that, the average value of plating thickness and the standard deviation of plating thickness were determined by sampling 20 x 30 mm test pieces at positions 50 mm from the two edges of the steel sheet in the width direction, the center, and intermediate positions between the positions 50 mm from the two edges and the center, that is, a total of five locations. The test pieces were cut, examined in cross-section, calculated for thickness at the front and back, measured for thickness at 10 points, and calculated for average value of thickness and standard deviation. [OlOl] The aluminum plating conditions, hot stamping conditions, mean linear intercept length, average value of thickness, and results of evaluation of the post painting anticorrosion property and weldability are described in Table 2. [0102] Further, simultaneously, the cross-sectional hardness was measured by a Vicker's hardness meter (load 1 kgf), but values of a hardness of 420 or more were obtained at all measured locations. [ 0 10 3 ] Table 1 Steel ingredients (mass%) C 0.22 Si 0.19 Mn 1.24 A1 0.04 P 0.02 S 0.014 N 0.005 Ti 0.02 B 0.003 Cr 0.12 [0104] Table 2 [OlOS] As shown by the results of evaluation of Table 2, test pieces of the aluminum plating conditions A and B were both hot stamped under the same conditions, but differences were observed in the obtained alloy layer structures (mean linear intercept lengths). Examples with large mean linear intercept lengths fell relatively in post painting anticorrosion property. The reason is believed to be the plating cracks. [0106] That is, the invention examples were all excellent in post painting anticorrosion property and spot weldability, but in the comparative examples where the mean linear intercept lengths failed to satisfy the requirements of the present invention (Nos. 4, 5, lo), the post painting anticorrosion property was inferior. Samples plated with A1 by the conditions of A were used for rapid heating and quenching in a flat plate die. The heating method used a near infrared heating furnace. The temperature elevation rate at that time was 50°C/sec. The peak sheet temperature and the holding conditions were also changed to investigate the structures of the plating layers at that time. The results and the results of Table 2 are summarized in FIG. 4. It is shown that the mean linear intercept length is dependent on the plating conditions and the heating conditions. [0107] Example 2 Cold rolled steel sheets of the various steel ingredients (A to I) which are shown in Table 3 (sheet thickness 1 to 2 mrn) were used for aluminum plating in the same way as in Example 1. In this example, the annealing temperature and the reducing furnace time at this time were changed. As the aluminum plating bath composition, by mass%, Si: 9% and Fe: 2% were contained. The bath temperature was 660°C and the deposition after plating was adjusted by the gas wiping method to a total of the two surfaces of 160 g/m2. [OlOS] After this, a method similar to Example 1 was used to make the heating temperature at the time of hot stamping 950°C for quenching. After that, the post painting anticorrosion property and the spot weldability were evaluated. The method of evaluation was the same as in Example 1. The Vicker's hardness was 420 or more in 5 all cases. [ 0 11 0 ] Table 4 I 4 P I No. 1 Steel A 7 8 9 10 11 12 Sheet thickness (mm) 1.2 D E F G H I Annealing temp. ("C) 740 1.6 1.6 1.6 2.0 1.2 1.6 Reducing time (s~c) 4 0 7 2 0 730 740 7 4 0 740 7 4 0 Plating thickness average (pm) 2 8 5 0 5 0 5 0 6 5 4 0 5 0 Plating thickness standard deviation 2.5 2 9 2 8 2 8 2 8 2 8 Standard deviation/ average 0.09 3.3 3.2 3.0 4.4 2.6 Mean linear intercept length (pm) 12 2 8 0.11 0.11 0.11 0.16 0.10 Post painting anticorrosion property Very Good Good 12 13 12 12 12 Inv. ex. Spot weldability Good Remarks Inv. ex. Very Good Very Good Very Good Poor Very Good Good Good Good Poor Good Inv. ex. Inv. ex. Inv. ex. Comp. ex. Inv. ex. [0111] In Example 2, the ingredients of the steel used, the sheet thickness, and the aluminum plating bath components were changed. As shown by the results of evaluation of Table 4, a trend was observed where if the sheet thickness becomes larger, the standard deviation of the plating thickness becomes larger and, further, if the annealing temperature becomes higher, the standard deviation of the plating thickness becomes larger. If the standard deviation is large, the suitable weld current range is narrow and spattering was easily generated in spot welding. Further, in a system of ingredients with high Si such as the Steel Ingredients G, if the furnace time in the reducing furnace is long (65 sec), nonplating defects are deemed to occur and the post painting anticorrosion property fell. [0112] That is, as shown by the results of evaluation of Table 4, the invention examples were all excellent in post painting anticorrosion property and spot weldability, but in a comparative example where the ratio of the average value of thickness to the standard deviation of thickness (standard deviation/average) exceeds 0.15 (No. 4), the spot weldability was inferior. Further, in a comparative example where the reducing furnace time was long and the standard deviation/average exceeded 0.15 (No. lo), both the post painting anticorrosion property and spot weldability were inferior. [0113] Example 3 The aluminum plated steel sheets of Nos. 2 and 5 of Table 4 of Example 2 were box annealed to alloy the aluminum plating layers. At this time, No. 2 corresponded to the Steel Ingredients A and No. 5 to the Steel Ingredients B. These differed in the amounts of Cr in the steel. At this time, in No. 2 (Steel Ingredients A), at the time of box annealing, A1N was formed near the interface of the aluminum plating layer and the steel sheet and the aluminum plating layer could not be sufficiently alloyed. In No. 5 (Steel Ingredients B), alloying was possible. Using No. 5, an ohmic heating means was used to raise the temperature by a temperature elevation rate of 200°C/sec up to 950°Cf then the sheet was quenched without holding. 5 The box annealing caused the aluminum plating layer to become alloyed, so even after ohmic heating, the thickness of the A1-Fe alloy layer was constant. The post painting anticorrosion property and spot weldability were evaluated by similar methods to Example 1, whereupon the 10 post painting anticorrosion property was evaluated as being "very good" and the spot weldability as being "good", that is, excellent properties were shown. The Vicker's hardness was also shown to be 482. [ 0 11 4 1 Example 4 15 The steel of Table 1 of Example 1 was used for aluminum plating under the aluminum plating conditions B of Example 1. At this time, the plating coating deposition amount was adjusted to a total of the two sides of 80 to 160 g/m2. Furthermore, after the aluminum plating, a 20 mixture of a finely dispersed ZnO aqueous solution (Nanotech Slurry made by C.I. Kasei) and a urethane-based water-soluble resin was coated by a roll coater and dried at 80°C. At this time, the amounts of deposition of the ZnO film were, converted to Zn, 0.5 to 3 g/m2. These test 25 pieces were hot stamping and quenched. [0115] As the hot stamping conditions at this time, in addition to the furnace heating which is shown in Example 1, an infrared heating furnace was also used. The holding time in the case of furnace heating was 60 sec, while in 30 the case of infrared heating was also 60 sec. Note that, the temperature elevation rate in the infrared heating was approximately 19OC/sec. The thus prepared test piece was evaluated by the same method as in Example 1. The results of evaluation at this time are shown in Table 5. 35 The Vicker's hardness was 420 or more in all cases. [0116] Table 5 [0117] Test pieces given a ZnO film exhibited excellent post painting anticorrosion property even with a small deposition amount. Further, the spot weldability was also excellent. CLAIMS Claim 1. A hot stamped high strength part which is excellent in post painting anticorrosion property, comprising an alloy plating layer comprising an A1-Fe intermetallic compound phase on the surface of the steel sheet, said alloy plating layer is comprised from phases of a plurality of intermetallic compounds, a mean linear intercept length of crystal grains of a phase containing Al: 40 to 65 mass% among said phases of the plurality of intermetallic compounds is 3 to 20 pm, an average value of thickness of said A1-Fe alloy plating layer is 10 to 50 pm, and a ratio of the average value of thickness to the standard deviation of thickness of said A1-Fe alloy plating layer satisfies the following relationship: O