mame of Document] DESCRIPTION [Title of the Invention] HIGH-CORROSION-RESISTANCE HOT-DIP GALVANIZED STEEL SHEET HAVING EXCELLENT APPEARANCE UNIFORMITY AND MANUFACTURING METHOD THEREOF [Technical Field] [0001] The present invention relates to a hot-dip galvanized steel sheet. More specifically, the present invention relates to a high-corrosion-resistance hot-dip galvanized steel sheet that has excellent appearance uniformity regardless of uniformity of cleanliness of a base steel sheet and is applicable as steel sheets for various uses of for example, home electric appliances, automobiles, and building materials. [Background Art] [0002] There is a hot-dip galvanized steel sheet to be used as a steel sheet having good corrosion resistance. This hot-dip galvanized steel sheet is widely used in various manufacturing industries such as in automobile, home electric appliance, and building material fields. [0003] As a manufacturing method of the hot-dip galvanized steel sheet, a method in which a cold-rolled steel sheet or a hot-rolled steel sheet is used as a base steel sheet and the base steel sheet is passed through a continuous hot-dip galvanizing line, (which will be referred to as a CGL, hereinafter), to manufacture a hot-dip galvanized steel sheet is general. As a process of the CGL, it is general to use a total reducing furnace method in which in a cleaning section on the entrance side, the base steel sheet is subjected to alkaline spray degreasing and then is subjected to brush cleaning, and in an annealing section, is subjected to annealing in a reducing atmosphere to be dipped in a hot-dip galvanizing bath. Further, there is also a case to use a Sendzimir method in which at the stage prior to the annealing section, a non-oxidizing furnace is provided, and the surface-cleaned base steel sheet is preliminarily heated in the non-oxidizing furnace and then is subjected to reduction annealing in a reducing furnace to then be dipped into a hot-dip galvanizing bath. [0004] For the purpose of further improving corrosion resistance of a hot-dip galvanized steel sheet manufactured by the process as described above, there has been proposed a high-corrosion-resistance hot-dip galvanized steel sheet with a hot-dip galvanizing layer having A1 and Mg added thereto. For example, in Patent Document 1, there has been proposed a hot-dip Zn-Al-Mg-Si coated steel sheet. Further, in Patent Document 1, it has been proposed that to this hot-dip Zn-Al-Mg-Si coated steel sheet, one or two or more of Ca, Be, Ti, Cu, Ni, Co, Cr, and Mn islare added, to thereby make it possible to obtain a coated steel sheet having further excellent corrosion resistance. [0005] Further, in Patent Document 2, it has been disclosed that Ti, B, and Si are added to a hot-dip Zn-Al-Mg coated steel sheet to thereby improve its outward appearance. [Prior Art Document] [Patent Document] [0006] Patent Document 1: International Publication No. W02000/07 1773 Patent Document 2: Japanese Laid-open Patent Publication No. 2001-29501 5 [Disclosure of the Invention] [Problems to Be Solved by the Invention] [0007] However, in the above-described coated steel sheets, and additionally in coated steel sheets that have been disclosed up to now, appearance uniformity has not been secured enough to be satisfactory. [OOOS] A Zn-Al-Mg ternary alloy has a ternary eutectic point of a composition of 3 mass% Mg - 4 mass% A1 - 93 mass% Zn, and thus when hot-dip coating is performed by using a coating bath having a composition with concentration of A1 higher than it, a coating layer is mainly constituted of three types of phases of an A1 phase, an MgZn2 phase, and an A1/MgZn2/Zn ternary eutectic phase. Further, when the coating layer contains Si in addition to Zn, Al, and Mg, it is mainly constituted of four types of phases including an Mg2Si phase, in addition to the above-described three types of phases. [0009] In FIG. 1, there is shown an example of a cross-sectional structure of a hot-dip Zn-Al-Mg-Si coating layer constituted of constituent phases as above. 1 denotes a coating original sheet, each 2 denotes an A1 phase, each 3 denotes an MgZn2 phase, each 4 denotes an A1/MgZn2/Zn ternary eutectic phase, and each 5 denotes an Mg2Si phase. [0010] In FIG 2, there is shown an example of an outward appearance of the hot-dip Zn-Al-Mg-Si coating layer having the cross-sectional structure as shown in FIG. 1. 6 denotes a place where there are a lot of AVMgZn2/Zn ternary eutectic phases on a surface, which has a metallic luster. 7 denotes a place where A1 phases are exposed to the surface, which has a white appearance. [OOll] In hot-dip Zn-Al-Mg-Si coating, first, the Mg2Si phases are formed on a base steel sheet in a coating bath. Then, as described previously, when concentration of A1 is higher than a ternary eutectic point composition, in a cooling process after the base steel sheet is pulled out of the coating bath, the A1 phases crystallize in a dendrite form from a liquid phase. Subsequently, the MgZn2 phases crystallize and finally the A1/MgZn2/Zn ternary eutectic phases solidify, and solidification of the liquid phase is completed. The place where at the time of the solidification of the A1/MgZn2/Zn ternary eutectic phases, dendritic portions of the A1 phases being a primary crystal break through a surface of a melt to be exposed to the surface of the coating corresponds to the white portion denoted by 7 in FIG. 2. Further, the place where the A1/MgZn2/Zn ternary eutectic phases solidify so as to cover a surface layer of the coating layer corresponds to the metallic luster portion denoted by 6 in FIG 2. As there are more dendritic portions of the A1 phases exposed to the surface of the coating layer, degree of luster of a visual appearance of the whole coating layer becomes lower and degree of whiteness becomes higher. [0012] In the manufacturing process of the hot-dip galvanized steel sheet as described previously, when a rust preventive oil and a rolling oil on the surface of the coating original sheet are removed completely in the cleaning section on the entrance side of the CGL, and thereafter annealing and coating are performed, on the whole surface of the coating original sheet, solidification reaction from the liquid phase as described previously occurs uniformly in the order of the Mg2Si phase, the A1 phase, the MgZn2 phase, and the AVMgZn2/Zn ternary eutectic phase. As a result, on the whole surface of the coating layer, as shown in FIG. 2, the outward appearance of which the dendritic portions of the A1 phases are uniformly distributed in the A1/MgZn2/Zn ternary eutectic phases is obtained. [0013] However, in the cleaning section on the entrance side of the CGL, there is sometimes a case that the rust preventive oil and the rolling oil are accumulated in an alkaline degreasing liquid and thus degreasing ability of the degreasing liquid decreases and a cleaning brush is abraded partially and thus the cleaning becomes insufficient. When the cleaning becomes insufficient, oil-dirt is sometimes left locally on the base steel sheet even after the base steel sheet is passed through the cleaning section. [0014] In the CGL as above, it became clear that when annealing and coating are performed by using the base steel sheet on which oil-dirt is left locally, in the surface layer of the coating immediately on an oil-dirt portion, the degree of luster of the coating layer becomes extremely higher as compared to another portion. Such an oil-dirt remaining portion of the coating original sheet occurs locally and irregularly, so that a coating appearance such that a place with a high degree of luster is irregularly mixed in the appearance of which the dendritic portions of the A1 phases are uniformly distributed in the AVMgZn2/Zn ternary eutectic phases is obtained, to thus cause a problem that the appearance uniformity deteriorates. [00 1 51 However, in the technique disclosed in Patent Document 1 described above, no consideration is given to the appearance uniformity in the case when oil-dirt is locally left on the base steel sheet. Further, although one or two or more of Ca, Be, Ti, Cu, Ni, Co, Cr, and Mn islare added for the purpose of improving the corrosion resistance after the coating, no consideration is given to the problem that the appearance uniformity deteriorates by the local oil-dirt remaining on the base steel sheet. Further, in the technique disclosed in Patent Document 2 described above, although Ti and E are added for the purpose of suppressing generation and growth of ZnllMgz phases to deteriorate the outward appearance, no consideration is given to the problem of the deterioration of appearance uniformity ascribable to the local oil-dirt remaining on the base steel sheet. [0016] The present invention has been made in consideration of the above-described problems, and has an object to provide a high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity regardless of uniformity of cleanliness of a base steel sheet. [Means for Solving the Problems] [0017] The present inventors first examined the reason why in an oil-dirt remaining portion on a base steel sheet, degree of luster of a coating layer becomes high. As a result, immediately on the oil-dirt remaining portion on the base steel sheet, the size of an A1 phase being a primary crystal was not different fiom that of a normal portion at the time of solidification fiom a liquid phase after pulling out of a coating bath. However, it was ascertained that immediately on the oil-dirt remaining portion, the degree of luster increases because A1/MgZn2/Zn ternary eutectic phases being a final solidification phase are made fine. Next, they earnestly examined a method capable of securing the appearance uniformity even though the base steel sheet is such that oil-dirt is left locally thereon. As a result, it became clear that Ca phases each mainly composed of Ca or a Ca compound are made to exist at an interface between the coating layer and the base steel sheet, and thereby the A11MgZn2/Zn ternary eutectic phases are made fine regardless of presence or absence of oil-dirt on the base steel sheet. The present inventors found the new knowledge that the Al/MgZn2/Zn ternary eutectic phases are made fine by using the Ca phases as a starting point, and thereby the degree of luster of the coating layer increases overall and the appearance uniformity improves, and then reached completion of the present invention. [0018] That is, the gist of the present invention is as follows. [ll A high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity, includes: a coating layer containing Al: 4 to 22 mass%, Mg: 1 to 6 mass%, and Si: 0.001 to 1 mass%, and a balance being composed of Zn and inevitable impurities formed on a surface, in which at an interface between the coating layer and a base steel sheet, Mg2Si phases and Ca phases each mainly composed of Ca or a Ca compound exist, and at least part of the MgzSi phases precipitate by using the Ca phases as a nucleus. PI The high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to [I], in which a density of the MgzSi phases each having a circle-equivalent diameter of 2 pm or more out of the Mg2Si phases existing at the interface between the coating layer and the base steel sheet is 10 to 1000 pieces per 0.01 rnm2. [31 The high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to [I], in which an average diameter of A1/MgZn2/Zn ternary eutectic phases existing in the coating layer is 5 to 200 pm. [41 The high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to [I], in which the coating layer further contains 0.000001 to 0.5 mass% of one or two or more selected from Ti, Ni, Zr, Sr, Hf, Sc, and B alone or in combination. [51 A manufacturing method of a high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity, includes: a step of bonding Ca phases each mainly composed of Ca or a Ca compound to a surface of a base steel sheet; a step of annealing the base steel sheet having had the Ca phases bonded to the surface; and a step of dipping the base steel sheet into a hot-dip galvanizing bath containing Al: 4 to 22 mass%, Mg: 1 to 6 mass%, and Si: 0.001 to 1 mass%, and a balance being composed of Zn and inevitable impurities and performing hot-dip galvanizing. [61 The manufacturing method of the high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity according to [5], in which in the step of bonding Ca or a Ca compound to the surface of the base steel sheet, the base steel sheet is dipped into a hot water containing Ca of 10 to 40 mass ppm and having a temperature of 50 to 90°C for 1 to 100 s. [Effect of the Invention] LOO 191 According to the present invention, there is provided a high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity regardless of uniformity of cleanliness of a base steel sheet. [Brief Description of the Drawings] [0020] [FIG. 11 FIG. 1 are views each showing one example of a cross-sectional structure of a hot-dip Zn-Al-Mg-Si coated steel sheet, and FIG l(a) is a micrograph of a coating layer (2000 magnifications) and FIG. 1(b) is a view showing a distribution state of respective structures in the micrograph; [FIG. 21 FIG. 2 is a photograph showing one example of an outward appearance of the hot-dip Zn-Al-Mg-Si coated steel sheet; [FIG. 31 FIG. 3 are views each showing one example of data obtained by performing a cross-sectional EPMA analysis on a hot-dip galvanized steel sheet of the present invention, and FIG. 3(a) shows a result of an element distribution of Si, FIG. 3(b) shows a result of an element distribution of Mg, FIG. 3(c) shows a result of an element distribution of Ca, FIG. 3(d) shows a result of an element distribution of Zn, and FIG. 3(e) shows a cross-sectional structure of respective constituent phases estimated from the results of the EPMA analysis; [FIG. 41 FIG. 4 is a view showing one example of a profile of Zn, Fe, and Ca in a depth direction obtained by performing a GDS depth direction analysis on the hot-dip galvanized steel sheet of the present invention; [FIG. 51 FIG. 5 is a schematic view of a photograph of which a coating layer of the hot-dip galvanized steel sheet of the present invention is dissolved by 0.5% hydrochloric acid containing inhibitors and then its surface is photographed by an SEM at 2000 magnifications; and [FIG. 61 FIG. 6 is a view showing one example of data obtained after EBSD measurement is performed on the hot-dip galvanized steel sheet of the present invention for ~btaininga n average diameter of A1/MgZn2/Zn ternary eutectic phases and grain boundaries are drawn by a solid line. [Mode for Carrying out the Invention] [0021] Hereinafter, the present invention will be explained in detail. The present invention relates to a high-corrosion-resistance hot-dip galvanized steel sheet having excellent appearance uniformity that has a coating layer formed on a surface of a base steel sheet. [0022] (Base steel sheet) As a base steel sheet (coating original sheet) to be used for a base for coating, a hot-rolled steel sheet and a cold-rolled steel sheet can be both used, and a variety of steel types such as an A1 killed steel, an ultralow carbon steel sheet having Ti, Nb, and the like added thereto, a high-strength steel in which strengthening elements such as P, Si, and Mn are added to these, and a stainless steel can also be applied. Further, with regard to a hot rolling condition, a cold rolling condition, and so on, predetermined conditions may be selected according to the size of the steel sheet and the required strength, and