[0001]The present invention relates to a plated steel sheet.
Priority is claimed on Japanese Patent Application No. 2019-080288, filed on
April19, 2019, the content of which is incorporated herein by reference.
[Related Art]
[0002]
Recently, in the building material field or the like, the development of a hot-dip
Zn-Al-Mg-based plated steel sheet has progressed.
[0003]
Patent Document 1 discloses a hot-dip Al-Zn alloy plated steel sheet including
a plating layer, in which the plating layer includes, by mass%, Al: 25% to 90% and Sn:
0.01% to 10% and further includes 0.01% to 10% of one kind or more selected from the
group consisting of Mg, Ca, and Sr.
[0004]
Patent Document 2 discloses a chemical conversion steel sheet, in which a hotdip
Zn-Al-Mg alloy plated steel sheet where a proportion of [Al/Zn/Zn2Mg ternary
eutectic structure] in an outermost surface of a plating layer is 60 area% or more is a
substrate, the plating layer surface is covered with a precipitate layer including at least
one kind selected from the group consisting of Ni, Co, Fe, and Mn and where the total
adhesion amount of Ni, Co, and Fe is in a range of 0.05 mg/m2 to 5.0 mg/m2 and the
adhesion amount of Mn is in a range of 0.05 mg/m2 to 30 mg/m2, a phosphate film
formed of a phosphate crystal having an average grain size of 0.5 ~m to 5.0 ~m, and a
- 1 -
chemical conversion film where a valve metal oxide or hydroxide and a valve metal
fluoride are present together, the phosphate crystal rises from the plating layer by a base
portion being buried in the plating layer, and the chemical conversion film is an organic
resin film formed on an interface reaction layer at an interface with the plating layer or
the precipitate layer exposed between the phosphate crystal grains.
[0005]
Patent Document 3 discloses a zinc-based alloy-plated steel including a zincbased
alloy plating layer that is formed on a surface of a steel, in which the zinc-based
alloy plating layer includes, by mass%, Mg: 1% to 10%, Al: 2% to 19%, Si: 0.01% to
2%, Fe: 2% to 75%, and a remainder consisting of Zn and unavoidable impurities.
[0006]
In addition, Patent Document 4 discloses a technique of adding Mg to an AlZn-
based plating layer in order to provide zinc-based alloy-plated steel having excellent
corrosion resistance and weldability.
[0007]
However, when the techniques disclosed in Patent Documents 1 to 4 are
applied to vehicles, an Al oxide is formed on a plating layer surface due to Al in the
plating layer. As a result, chemical convertibility deteriorates. In particular, in Patent
Document 4, a large amount of a Fe-Zn phase that deteriorates chemical convertibility is
formed in the plating layer.
[0008]
Under these circumstances, it is desired to develop a plated steel sheet having
excellent chemical convertibility that is suitable for a vehicle.
[Prior Art Document]
[Patent Document]
- 2 -
[0009]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. 2015-214747
[Patent Document 2] Japanese Patent No. 4579715
[Patent Document 3] Japanese Unexamined Patent Application, First
Publication No. 2009-120947
[Patent Document 4] Japanese Unexamined Patent Application, First
Publication No. 2009-120947
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0010]
The present invention has been made in consideration of the above-described
circumstances, and an object thereof is to provide a plated steel sheet having excellent
chemical convertibility.
[Means for Solving the Problem]
[0011]
In order to achieve the object, the present invention adopts the following
configurations.
That is, according to one aspect of the present invention, there is provided a
plated steel sheet including: a steel; and a plating layer that is provided on a surface of
the steel, in which the plating layer includes, by mass%, Al: 5.00% to 35.00%, Mg:
2.50% to 13.00%, Fe: 5.00% to 35.00%, Si: 0% to 2.00%, Ca: 0.03% to 2.00%, and a
remainder consisting of Zn and impurities, and in a surface of the plating layer, the area
fraction of a Fe-Al phase is 0% to 30%, the area fraction of a rod-like lamellar structure
of Zn and MgZn2 is 5% to 90%, the area fraction of a massive MgZn2 phase is 10% to
- 3 -
70%, and the area fraction of a remainder is 10% or less.
[0012]
Here, the plating layer may include, by mass%, Al: 10.00% to 30.00%.
[0013]
Here, the plating layer may include, by mass%, Mg: 3.00% to 10.00%.
[0014]
Here, the plating layer may include, by mass%, Mg: 4.00% or more.
[0015]
In addition, the plating layer may include, by mass%, Ca: 0.03% to 1.00%.
[0016]
In addition, in the surface of the plating layer, the area fraction of the lamellar
structure may be 10% to 60%.
[0017]
In addition, in the surface of the plating layer, the area fraction of an Al-Zn
dendrite mainly formed of anAl phase and a Zn phase may be 5% or less.
[0018]
In addition, in the surface of the plating layer, the area fraction of a
Zn/Al/MgZn2 ternary eutectic structure may be 5% or less.
[0019]
In addition, in the surface of the plating layer, the area fraction of a massive Zn
phase may be 10% or less.
[0020]
In addition, in the surface of the plating layer, the area fraction of a plate-like
Zn/MgZn2 lamellar structure may be 10% or less.
[0021]
- 4 -
In addition, in the surface of the plating layer, the area fraction of a Mg2Si
phase may be 10% or less.
[Effects of the Invention]
[0022]
According to the aspect of the present invention, a plated steel sheet having
excellent chemical convertibility can be provided.
[Brief Description of the Drawings]
[0023]
FIG. 1 is a SEM image showing a surface structure of a plating layer according
to an embodiment.
FIG. 2 is a SEM image showing a surface structure of a plating layer in the
related art.
[Embodiments of the Invention]
[0024]
Hereinafter, a plated steel sheet according to an embodiment having excellent
chemical convertibility and a method of manufacturing the same will be described. In
the embodiment, a numerical range represented using "to" refers to a range including
numerical values before and after "to" as a lower limit and an upper limit.
[0025]
[Plated Steel Sheet]
The plated steel sheet according to the embodiment includes: a steel; and a
plating layer that is provided on a surface of the steel,
in which the plating layer includes, by mass%,
Al: 5.00% to 35.00%,
Mg: 2.50% to 13.00%,
- 5 -
Fe: 5.00% to 35.00%,
Si: 0% to 2.00%,
Ca: 0% to 2.00%, and
a remainder consisting of Zn and impurities, and
in a surface of the plating layer, the area fraction of a Fe-Al phase is 0% to
30%, the area fraction of a rod-like lamellar structure of Zn and MgZn2 is 5% to 90%,
the area fraction of a massive MgZn2 phase is 10% to 70%, and the area fraction of a
remainder is 10% or less. That is, in the embodiment, by actively forming the rod-like
lamellar structure of Zn and MgZn2 having excellent chemical convertibility, the
massive MgZn2 phase, and preferably the Fe-Al phase in the plating layer and
suppressing the formation of a phase that deteriorates chemical convertibility, for
example, an Al-Zn dendrite or a Fe-Zn phase, the chemical convertibility of the plated
steel sheet is improved. Further, the plated steel sheet according to the embodiment
includes a large amount of the rod -like lamellar structure of Zn and MgZn2. Therefore,
liquid metal embrittlement (LME) during spot welding can also be suitably prevented
(excellent LME resistance can be obtained).
[0026]

The material of the steel (base steel sheet) as a base material of the plated steel
sheet is not particularly limited. General steel, Ni-precoated steel, Al-killed steel, or
some high alloy steel can be used. The shape of the steel is also not particularly
limited.
[0027]

The plated steel sheet according to the embodiment having excellent chemical
- 6 -
convertibility includes a plating layer that is formed on a surface of the steel.
[0028]
(Chemical Composition)
Next, a chemical composition of the plating layer will be described. In the
following description, unless specified otherwise, "%"represents "mass%".
[0029]
Al: 5.0% to 35.00%
Al is an element that is necessary to contain an element other than Zn in the
plating layer. Originally, in a Zn plating layer (Zn layer), another element is not likely
to be contained, for example, a high concentration of Mg cannot be added. However,
by containing Al in the plating layer (Zn-based plating layer), a plating layer containing
Mg can be manufactured. Further, Fe dispersed in the plating layer in the alloying
process reacts (is alloyed) withAl prior to Zn such that the Fe-Al phase (for example,
Fe2Als phase) having excellent post-coating corrosion resistance and LME resistance
can be formed. Further, the formation of a Fe-Zn phase that deteriorates post-coating
corrosion resistance in the alloying process can be suppressed. It is not necessary that
the Fe-Al phase is formed in the plating layer. However, when the Fe-Al phase is
formed in the plating layer, post-coating corrosion resistance and LME resistance can be
further improved. In addition, in order to suppress the formation of the Fe-Zn phase,
Mg addition is also effective, and this effect is exhibited particularly when the Mg
concentration is 2.50% or more. The Mg concentration is more preferably 4.00% or
more.
[0030]
When the Al concentration is less than 5.00%, inclusion of Mg and an alloying
element imparting performance to the plating layer tends to be difficult. In addition,
- 7 -
Al has a low density, and thus a larger amount of an Al phase in terms of mass content is
formed as compared to Zn. However, when the Al concentration is less than 5.00%,
most of the plating layer tends to be a Zn phase. As a result, chemical convertibility
also deteriorates significantly. It is not preferable that the Zn phase is the first phase in
the plating layer from the viewpoint of chemical convertibility.
In addition, when the Al concentration is less than 5.0%, in a case where Mg is
added, a large amount of dross is formed on the plating bath, and the plated steel sheet
cannot be manufactured. Accordingly, the Al concentration is 5.0% or more,
preferably 5.00% or more and more preferably 10.00% or more.
[0031]
On the other hand, when the Al concentration increases excessively, the
proportion of the Al phase in the plating layer increases rapidly, the proportion of the
rod-like Zn/MgZn2lamellar structure necessary to impart chemical convertibility
decreases, and the proportion of the Fe-Al phase increases excessively, which is not
preferable. Therefore, the Al concentration is 35.00% or less and preferably 30.00% or
less.
This way, in the embodiment, by balancing the Al concentration and a Fe
concentration described below (adjusting the concentrations to be in predetermined
concentration ranges), Al reacts actively with Fe to form the Fe-Al phase.
Accordingly, in the embodiment, by causing Alto be mainly present as the Fe-Al phase
in the plating layer, the amount of Al present as the Al phase can be reduced. As a
result, the amount of a dendrite mainly formed of anAl phase and a Zn phase that
causes deterioration in corrosion resistance can be reduced.
[0032]
Mg: 2.50% to 13.00%
- 8 -
Mg is an element that is necessary to impart chemical convertibility. When
Mg is added to a Zn-based plating layer, Mg forms MgZn2 as an intermetallic
compound. Further, Mg also has a characteristic in that the formation of the Fe-Zn
phase is suppressed. The Mg concentration that is the minimum necessary to
sufficient! y improve the chemical convertibility of the plating layer and to suppress the
formation of the Fe-Zn phase is 2.50%. Therefore, the Mg concentration is 2.50% or
more, preferably 3.00% or more, and more preferably 4.00% or more.
On the other hand, when the Mg concentration is more than 13.00%, the
amount of the MgZn2 phase rapidly increases, the plastic deformability of the plating
layer is lost, and the workability deteriorates, which is not preferable. Accordingly, the
Mg concentration is 13.00% or less, preferably 11.00% or less, and more preferably
10.00% or less.
This way, in the embodiment, by adding predetermined amounts of Al and Mg
to the plating layer, the formation of the Fe-Zn phase is suppressed. Therefore, in the
embodiment, the Fe-Zn phase is not substantially present in the plating layer. In
particular, the Fe-Zn phase deteriorates the post-coating corrosion resistance and, when
the coating surface is damaged, is likely to cause red rust to occur. Therefore, it is
preferable that the formation of the Fe-Zn phase is suppressed as much as possible.
Examples of the type of the Fe-Zn phase include y phase, 8 phase, and s phase. In
order to suppress the formation of the Fe-Zn phase, it is necessary that the chemical
composition of the plating layer is adjusted to the composition according to the
embodiment (in particular, the Al concentration and the Mg concentration are
important) and the alloying temperature is 440°C to 480°C.
[0033]
Fe: 5.00% to 35.00%
- 9 -
When the Fe concentration is less than 5.00%, the Fe content is insufficient,
and the amount of the Fe-Al phase is small, which is not preferable. In addition, when
the Fe concentration is less than 5.00%, the area ratio of the Al-Zn dendrite not
contributing to the improvement of the chemical convertibility may be more than 5%,
which is not preferable. Therefore, the Fe concentration is 5.00% or more, preferably
10.00% or more, and more preferably 15.00% or more.
When the Fe concentration is more than 35.00%, a desired metallographic
structure may not be formed in the plating layer according to the embodiment. As the
amount of the Fe component increases, the potential increases, appropriate sacrificial
protection ability for the steel cannot be maintained, and the corrosion rate may
increase, which is not preferable. Therefore, the Fe concentration is 35.00% or less,
preferably 30.00% or less, and more preferably 25.00% or less.
In addition, regarding the Fe concentration relative to the Al concentration,
Fe/ Al is preferably 0.9 to 1.2. By adjusting Fe/ Al to be in the above-described range,
the Fe2Als phase is likely to be formed.
When Fe/Al is less than 0.9, it is difficult to form a sufficient amount of the
Fe2Als phase, and thus an excess amount of the dendrite formed of the Al phase and the
Zn phase is formed.
In addition, when Fe/ Al is more than 1.2, a Fe-Zn-based intermetallic
compound phase is likely to be formed. Even in this case, the Fe2Als phase is not
likely to be formed.
[0034]
Si: 0% to 2.00%
Si is an element that is effective for improving adhesion between the steel and
the plating layer. Therefore, Si may be contained in the plating layer. Si is not
- 10 -
necessarily contained in the plating layer. Therefore, the lower limit of the Si
concentration is 0%. The adhesion improvement effect by Si is exhibited when the Si
concentration in the plating layer is 0.03% or more. Therefore, when Si is contained in
the plating layer, the Si concentration is preferably 0.03% or more.
On the other hand, even when the Si concentration in the plating layer is more
than 2.00%, the adhesion improvement effect by Si is saturated. Therefore, even when
Si is contained in the plating layer, the Si concentration is set to be 2.00% or less. The
Si concentration is preferably 1.00% or less.
[0035]
Ca: 0.03% to 2.00%
Ca is an element that is effective for improving the chemical convertibility of
the plated steel sheet. Therefore, Ca may be contained in the plating layer. The
chemical convertibility improvement effect by Ca is exhibited when the Ca
concentration in the plating layer is 0.03% or more. Accordingly, theCa concentration
is 0.03% or more and preferably 0.05% or more.
On the other hand, even when the Ca concentration in the plating layer is more
than 2.00%, the chemical convertibility improvement effect by Ca is saturated.
Therefore, even when Ca is contained in the plating layer, the Ca concentration is set to
be 2.00% or less. The Ca concentration is preferably 1.00% or less.
[0036]
Remainder: Zn and impurities
The remainder other than Al, Mg, Fe, Si, and Ca consists of Zn and impurities.
Here, the impurities refer to elements that are unavoidably incorporated in the process
of plating, and the total amount of the impurities may be about 3.00%. That is, the
amount of the impurities in the plating layer may be 3.00% or less.
- 11 -
Examples of elements that may be contained as the impurities and the
concentrations of the elements include Sb: 0% to 0.50%, Pb: 0% to 0.50%, Cu: 0% to
1.00%, Sn: 0% to 1.00%, Ti: 0% to 1.00%, Sr: 0% to 0.50%, Ni: 0% to 1.00%, and Mn:
0% to 1.00%. When the impurity elements having concentrations higher than the
above-described ranges are contained in the plating layer, it is difficult to obtain the
desired characteristics, which is not preferable.
[0037]
The chemical composition of the plating layer can be measured, for example,
using the following method. First, an acid solution is obtained by peeling and
dissolving the plating layer with an acid containing an inhibitor that suppresses the
corrosion of the base metal (steel). Next, by measuring the obtained acid solution by
ICP analysis, the chemical composition (the kinds and contents of the chemical
components) of the plating layer can be obtained. The kind of the acid is not
particularly limited as long as it is an acid that can dissolve the plating layer. In this
measurement method, the chemical composition is measured as the average chemical
composition of the entire plating layer as a target to be measured. In Examples
described below, the chemical components (chemical composition) of the plating layer
were measured using this method.
[0038]
(Structure)
In a surface of the plating layer according to the embodiment, the area fraction
of a Fe-Al phase is 0% to 30%, the area fraction of a rod-like lamellar structure of Zn
and MgZn2 (Zn/MgZn2lamellar structure) is 5% to 90%, the area fraction of a massive
MgZn2 phase is 10% to 70%, and the area fraction of a remainder is 10% or less.
[0039]
- 12 -
FIG. 1 is a SEM image showing a surface structure of a plating layer 10
according to the embodiment. As shown in FIG. 1, when a surface of the plating layer
10 according to the embodiment is observed with a SEM, a rod-like lamellar structure
11 of Zn and MgZn2, a hexagonal massive MgZn2 phase 12, and a Fe-Al phase 13 are
observed.
[0040]
FIG. 2 is a SEM image showing a surface structure of a plating layer 100 in the
related art. The plating layer 100 according to the related art shown in FIG. 2 is
formed by performing hot-dip Zn-Al-Mg-based plating in the related art on steel.
As shown in FIG. 2, the alloying process is not performed on the plating layer
100 in the related art. Therefore, an Al-Zn dendrite 14 or a Zn/Al/MgZn2 ternary
eutectic structure 15 accounts for most of the plating layer 100, and a massive Zn phase
16 or a Mg2Si phase 17 is also observed. A massive MgZn2 phase 18 is not hexagonal,
and the rod-like lamellar structure of Zn and MgZn2, the hexagonal massive MgZn2
phase, and the Fe-Al phase are not observed.
Hereinafter, the structure of the plating layer according to the embodiment will
be described.
[0041]
Area Fraction of Fe-Al Phase: 0% to 30%
In the plated steel sheet according to the embodiment, it is preferable that, by
performing an alloying process after a hot-dip plating process described below, the FeAl
phase is formed in the plating layer. The Fe-Al phase according to the embodiment
is a phase containing an intermetallic compound of Fe and Al, and examples of the
intermetallic compound include Fe2Als and FeAl.
From the viewpoint of excellent chemical convertibility, it is preferable that the
- 13 -
Fe-Al phase is not exposed to the surface structure of the plating layer according to the
embodiment. The area fraction of the Fe-Al phase that does not deteriorate chemical
convertibility is 30%. Therefore, the upper limit of the Fe-Al phase is 30% and
preferably less than 20%.
The Fe-Al phase is an important structure from the viewpoint of obtaining
chemical convertibility and suitably preventing liquid metal embrittlement (LME)
during spot welding (obtaining excellent LME resistance).
[0042]
Area Fraction of Rod-like Zn/MgZn2 Lamellar Structure: 5% to 90%
The rod -like Zn/MgZn2 lamellar structure is a rod -like lamellar structure of a
Zn phase and a MgZn2 phase that is an intermetallic compound. Here, the rod shape
represents a microstructural morphology in which the three-dimensional shape of the
MgZn2 phase in the Zn/MgZn2 lamellar structure is a rod shape and the vicinity of the
rod-like MgZn2 phase is surrounded by the Zn phase. The rod-like Zn/MgZn2lamellar
structure is an important structure from the viewpoint that the plating layer according to
the embodiment exhibits suitable chemical convertibility. As described above, the
plating layer according to the embodiment contains Ca, and by rapid cooling the base
steel sheet at an average cooling rate of 20 °C/sec or faster after the alloying process
described below, the rod-like Zn/MgZn2lamellar structure is formed.
When the area fraction of the rod-like Zn/MgZn2lamellar structure is 5% or
more, suitable chemical convertibility can be obtained. Therefore, the area fraction of
the rod-like Zn/MgZn2lamellar structure is 5% or more and preferably 10% or more.
On the other hand, when the area fraction of the rod-like Zn/MgZn2lamellar
structure is more than 90%, the chemical convertibility improvement effect is saturated,
the plating layer surface becomes uneven due to eutectic solidification, and the external
- 14 -
appearance of the plated steel sheet deteriorates, which is not preferable. Therefore,
the area fraction of the rod-like Zn/MgZn2lamellar structure is 90% or less, preferably
70% or less, and more preferably 60% or less.
The rod -like Zn/MgZn2 lamellar structure is an important structure from the
viewpoint that the plated steel sheet can obtain not only chemical convertibility but also
desired LME resistance. The details of the mechanism is unclear, but the reason why
the rod-like Zn/MgZn2lamellar structure exhibits excellent LME resistance is presumed
to be that Ca is effectively contained in the structure.
[0043]
Area Fraction of Massive MgZn2 Phase: 10% to 70%
In order to obtain suitable chemical convertibility, the area fraction of the
massive MgZn2 phase having a hexagonal shape is preferably 10% or more and more
preferably 70% or more.
On the other hand, when the area fraction of the massive MgZn2 phase having
a hexagonal shape is more than 70%, the area fraction of the Fe-Al phase or the rod-like
Zn/MgZn2lamellar structure decreases excessively, and it is difficult to obtain suitable
chemical convertibility. Therefore, the area fraction of the massive MgZn2 phase is
70% or less.
[0044]
Area Fraction of Remainder: 10% or less
In order to obtain suitable chemical convertibility, the total area fraction of
structures in the remainder other than the Fe-Al phase, the rod-like Zn/MgZn2lamellar
structure, and the massive MgZn2 phase is 10% or less, preferably 7.5% or less, and
more preferably 5% or less.
Examples of the structures in the remainder include a plate-like Zn/MgZn2
- 15 -
lamellar structure described below, an Al-Zn dendrite, a Zn/Al/MgZn2 ternary eutectic
structure, a massive Zn phase, and a Mg2Si phase described below. Each of these
structures in the remainder will be described below.
[0045]
Plate-like Zn/MgZn2 Lamellar Structure: 10% or less
The plate-like Zn/MgZn2 lamellar structure is a plate-like lamellar structure of
a Zn phase and a MgZn2 phase that is an intermetallic compound. As described above,
the rod-like Zn/MgZn2lamellar structure is a structure necessary to obtain chemical
convertibility, but the plate-like Zn/MgZn2 lamellar structure does not contribute to
chemical convertibility. Therefore, from the viewpoint of obtaining suitable chemical
convertibility, the area fraction of the plate-like Zn/MgZn2 lamellar structure is 10% or
less and preferably 5% or less.
The rod -like Zn/MgZn2 lamellar structure and the plate-like Zn/MgZn2
lamellar structure are distinguished from each other in the difference in the
microstructural morphology and in whether the MgZn2 phase is rod-like or plate-like.
Here, as described above, the rod shape represents a microstructural morphology in
which the three-dimensional shape of the MgZn2 phase in the Zn/MgZn2 lamellar
structure is a rod shape and the vicinity of the rod -like MgZn2 phase is surrounded by
the Zn phase. The plate shape represents that the three-dimensional shape of the
MgZn2 phase in the Zn/MgZn2 lamellar structure is a plate shape. That is, in the platelike
Zn/MgZn2lamellar structure, a structure where the plate-like Zn phase and the
plate-like MgZn2 phase are alternate! y laminated is formed.
The three-dimensional shape of the MgZn2 phase can be inspected by cutting
the metallographic structure in a depth direction by mechanical polishing or FIB cutting
and observing the metallographic structure.
- 16 -
[0046]
Area Fraction of Dendrite (Al-Zn Dendrite) mainly formed of Al Phase and Zn
Phase: 5% or less
When the plating layer is formed, in the process of cooling the steel sheet from
a bath temperature after the hot-dip plating process described below, first, anAl primary
phase (a-(Zn,Al) phase crystallized as the primary phase) is crystallized and grows
dendritically (hereinafter, also referred to as "Al-Zn dendrite"). Next, by heating the
steel sheet in a temperature range of 440°C to 480°C to perform the alloying process,
most of the Al-Zn dendrite is substantially replaced with another structure, but a part of
the Al-Zn dendrite remains even after the alloying process.
The Al-Zn dendrite does not preferably affect chemical convertibility or LME
resistance. Therefore, the area fraction of the Al-Zn dendrite is as low as possible.
Therefore, in the plating layer according to the embodiment, the area fraction of the AlZn
dendrite is 5% or less and more preferably 3% or less.
"Mainly" represents that about 15% or more of the Al phase and the Zn phase
are contained in the dendrite by area fraction, and 5% or less of Fe, 3% or less of Mg,
and 1% or less of steel component elements (Ni, Mn) may be contained as the
remainder other than the Al phase and the Zn phase.
[0047]
Area Fraction of Zn/Al/MgZn2 Ternary Eutectic Structure: 5% or less
The Zn/ Al/MgZn2 ternary eutectic structure is a layered structure including a
Zn layer, an Allayer, and a MgZn2 layer that is formed of a Zn phase, an Al phase, and a
MgZn2 phase finally solidified in the outside of the Al primary phase due to a Zn-AlMg-
based eutectic reaction. The Zn/ Al/MgZn2 ternary eutectic structure also has the
chemical convertibility improvement effect, but the improvement effect thereof is lower
- 17 -
than that of the Fe-Al phase or the rod-like Zn/MgZn2 lamellar structure. Therefore,
the area fraction of the Zn/ Al/MgZn2 ternary eutectic structure is preferably as low as
possible. Therefore, in the plating layer according to the embodiment, the area fraction
of the Zn/ Al/MgZn2 ternary eutectic structure is preferably 5% or less and more
preferably 3% or less.
[0048]
Massive Zn Phase: 10% or Less
The massive Zn phase is a structure that may be formed when the Mg content
in the plating layer is low. When the massive Zn phase is formed, the blister width
tends to increase. The area ratio is preferably as low as possible and is preferably 10%
or less. The massive Zn phase is a phase different from the Zn phase in the Zn/MgZn2
binary eutectic structure. The massive Zn phase has a dendritic shape and may also be
observed to be circular on the cross sectional structure.
[0049]
Other Intermetallic Compound Phase: 10% or less
Other intermetallic compound phases do not preferably affect chemical
convertibility. Therefore, the area fraction of the other intermetallic compound phases
is preferably 10% or less and more preferably 5% or less. Examples of the other
intermetallic compound phase include a Mg2SiCaZnu phase, an AhCaSh phase, and an
AhCaZn2 phase.
[0050]
Unless specified otherwise, "area fraction" in the embodiment refers to an
arithmetic mean value when an area ratio of a desired structure in a plating layer surface
is calculated for arbitrarily selected five different samples. This area fraction
represents the volume fraction in the plating layer in practice.
- 18 -
[0051]

The area fraction of each of the structures in the plating layer is obtained using
the following method.
First, a plated steel sheet as a target to be measured is cut into 25 (c) x 25 (L)
mm, a surface SEM image of the plating layer and an element distribution image by
EDS are obtained. Regarding the area fractions of the constituent structures of the
plating layer, that is, the Fe-Al phase, the rod-like lamellar structure of Zn and MgZn2,
the massive MgZn2 phase, the Al-Zn dendrite, the Zn/Al/MgZn2 ternary eutectic
structure, the massive Zn phase, the plate-like Zn/MgZn2lamellar structure, the Mg2Si
phase, and the other intermetallic compound phase, one visual field is imaged from each
of five samples having different surface EDS mapping images of the plating layers, that
is, five visual fields (magnification: 1500-fold) in total are imaged, and the area fraction
of each of the structures is measured by image analysis. For example, in the EDS
mapping image, regions containing Fe, Zn, Al, Mg, and Si can be displayed by different
colors. Therefore, in this mapping image, a phase formed of Aland Fe is determined
to be the Fe-Al phase. In addition, in the mapping image, the structure formed of the
rod-like MgZn2 phase and the Zn phase surrounding the rod-like MgZn2 phase is
determined to be the rod -like Zn/MgZn2 lamellar structure. The other phases can be
determined using the same method. The area of the visual field may be, for example,
45 ~m x 60 ~m. The area fraction of each of the structures is obtained, for example, as
an arithmetic mean value of area fractions of each of the structures measured in the
respective visual fields (=(Area of Each of Structures in Any Visual field)/(Area of This
Visual field) x 1 00). In Examples described below, the area fraction of each of the
structures was measured using this method.
- 19 -
[0052]

The plated steel sheet according to the embodiment has excellent chemical
convertibility by including the steel and the plating layer having the above-described
characteristics.
In addition, the plated steel sheet according to the embodiment has excellent
LME resistance by including the steel and the plating layer having the above-described
characteristics. A chemical conversion film that is applicable to the plated steel sheet
according to the embodiment is not particular! y limited. For example, the chemical
conversion film may be a zinc phosphate film mainly formed of a hopeite as zinc
phosphate crystal.
[0053]
[Method of Manufacturing Plated Steel Sheet]
Next, a method of manufacturing the plated steel sheet according to the
embodiment will be described.
A method of manufacturing the plated steel sheet according to the embodiment
includes: a hot-dip plating process of dipping a base steel sheet in a plating bath
containing at least Al, Mg, Ca, and Zn to perform hot-dip plating; an alloying process of
heating the hot-dip plated base steel sheet at 440°C to 480°C for 2 to 8 seconds; and a
cooling process of cooling the plated steel sheet to 335°C at an average cooling rate of
20 °C/sec or faster.
[0054]

In the hot-dip plating process, a base steel sheet is dipped in a plating bath
containing at least Al, Mg, Ca, and Zn to perform hot-dip plating.
- 20 -
[0055]
In the hot-dip plating process, a so-called hot-dip plating method of adhering
the plating bath to the base steel sheet surface and pulling the base steel sheet from the
plating bath to solidify the molten metal adhered to the base steel sheet surface is used.
[0056]
(Plating Bath)
The composition of the plating bath is not particularly limited as long as it
contains at least Al, Mg, Ca, and Zn, and raw materials are prepared and dissolved in
the plating bath to achieve the composition of the above-described plating layer.
[0057]
The temperature of the plating bath is preferably in a range of higher than
380°C and 600°C or lower and may be in a range of 400°C to 600°C.
[0058]
It is preferable that the base steel sheet surface is reduced by heating the base
steel sheet in a reducing atmosphere before being dipped in the plating bath. For
example, a heat treatment is performed in a mixed atmosphere of nitrogen and hydrogen
at 600°C or higher, desirably 750°C or higher for 30 seconds or longer. After
completion of the reduction treatment, the base steel sheet is dipped in the plating bath
after being cooled to the temperature of the plating bath. The dipping time may be, for
example, 1 second or longer. When the base steel sheet dipped in the plating bath is
pulled, the plating adhesion amount is adjusted by gas wiping. The adhesion amount
to the single surface of the base steel sheet is preferably in a range of 10 g/m2 to 300
g/m2 and may be in a range of 20 g/m2 to 250 g/m2
.
[0059]

- 21 -
A method of manufacturing the plated steel sheet according to the embodiment
includes the alloying process of heating the hot-dip plated base steel sheet in a
temperature range of 440°C to 480°C for 2 to 8 seconds after the hot-dip plating
process. Through the alloying process, the plating layer having the desired structures
(that is, the structures having the above-described area fractions) is formed, and
excellent chemical convertibility can be obtained.
[0060]
In the alloying process, when the heating temperature (hereinafter, referred to
as "alloying temperature") is lower than 440°C, the alloying process is slow, which is
not preferable. Therefore, the alloying temperature is 440°C or higher.
On the other hand, when the alloying temperature is higher than 480°C,
alloying progresses excessively within a short period of time, and the alloying process
cannot be suitably controlled, which is not preferable. For example, in the alloying
process, Fe dispersed in the plating layer reacts withAl prior to Zn such that the Fe-Al
phase is formed. However, when alloying progresses excessively, redundant Fe that
does not react withAl reacts with Zn in the plating layer such that a large amount of the
Fe-Zn phase is formed. Therefore, the alloying temperature is 480°C or lower.
[0061]
In a case where the heating time (hereinafter, referred to as "alloying time") in
the alloying process is shorter than 2 seconds, when the hot dip-plated base steel sheet is
heated in a temperature range of 440°C to 480°C, the progress of alloying is
insufficient, which is not preferable. Therefore, the alloying time is 2 seconds or
longer.
On the other hand, when the alloying time is longer than 8 seconds, alloying
progresses significantly, which is not preferable. For example, a large amount of the
- 22 -
Fe-Zn phase is formed as in the case where the alloying temperature is excessively high.
Therefore, the alloying time is 8 seconds or shorter.
[0062]
In the alloying process, a heating method is not particularly limited. For
example, a heating method such as induction heating can be used.
[0063]

A method of manufacturing the plated steel sheet according to the embodiment
includes: a cooling process of cooling the plated steel sheet in a temperature range
(hereinafter, referred to as "cooling temperature range") from the alloying temperature
to 335°C at an average cooling rate of 20 °C/sec or faster after the alloying process.
[0064]
When the plated steel sheet is cooled in the cooling temperature range at an
average cooling rate of slower than 20 °C/sec, a suitable structure (in particular, the rodlike
Zn/MgZn2 lamellar structure) is not formed in the plating layer, which is not
preferable. Therefore, the average cooling rate in the cooling temperature range is
20 °C/sec or faster and preferably 25 °C/sec or faster.
[0065]
Through the above-described processes, the plated steel sheet according to the
embodiment can be manufactured.
The plated steel sheet according to the embodiment has excellent chemical
convertibility. In addition, the plated steel sheet according to the embodiment has
excellent LME resistance.
[Examples]
[0066]
- 23 -
[Example 1]

As a plated base steel sheet, a cold-rolled steel sheet (0.2% C-1.5% Si-2.6%
Mn) having a sheet thickness of 1.6 mm was used.
[0067]

Plating baths having different chemical compositions depending on Test No.
(level) were prepared such that a plating layer having a chemical composition shown in
Table 1 was formed on the base steel sheet. The chemical composition of the plating
layer was measured using the above-described method.
- 24 -
[0068]
[Table 1]
Plating Layer Component (mass%) Adhesion Amount of Plating Bath Manufacturing Conditions
Classification Impurities
Single Surface of temperature Alloying Alloying Cooling Rate to
No.
Zn Al Mg Fe Ca Si Plating Layer Temperature Time 335°C after Alloying
Kind of Element Total% (g/m2) (DC) (DC) (sec) (°C/sec)
Comparative Example 1 96.77 0.10 3.00 0.10 0.03 0.00 - 0 20 440 480 6 25
Comparative Example 2 87.60 5.00 2.00 5.00 0.20 0.20 - 0 40 455 480 6 25
Example 3 86.97 5.00 3.00 5.00 0.03 0.00 - 0 40 430 480 8 25
Example 4 84.45 5.10 5.10 5.10 0.10 0.00 Cu:0.1,Sr0.05 0.15 40 450 480 8 25
Example 5 73.00 9.90 7.10 9.90 0.10 0.00 - 0 40 470 480 8 25
Example 6 68.92 10.00 10.00 10.00 1.00 0.00 Sb:0.08 0.08 41 500 480 8 25
Comparative Example 7 72.90 10.10 6.80 10.10 0.10 0.00 - 0 42 460 480 20 25
Comparative Example 8 72.70 10.20 6.90 10.20 0.00 0.00 - 0 39 460 480 8 25
Example 9 74.74 11.00 3.00 11.00 0.03 0.20 Ti:0.03 0.03 150 460 480 8 25
Example 10 71.40 11.60 5.20 11.60 0.10 0.10 - 0 250 460 480 8 25
Example 11 62.80 15.50 6.10 15.50 0.10 0.00 - 0 40 480 480 8 25
Example 12 61.30 16.00 6.20 16.00 0.20 0.00 Ni:0.2, Mn0.1 0.3 10 480 480 8 25
Comparative Example 13 59.40 17.20 6.20 17.10 0.10 0.00 - 0 25 480 300 6 25
Comparative Example 14 57.40 18.20 6.10 18.20 0.10 0.00 - 0 41 480 - - 25
Comparative Example 15 59.40 17.20 6.30 17.00 0.10 0.00 - 0 42 480 580 8 25
Comparative Example 16 59.50 17.00 6.40 17.00 0.10 0.00 - 0 43 480 480 8 5
Example 17 62.29 17.30 3.00 17.20 0.20 0.00 Pb:0.01 0.01 41 500 480 6 25
Example 18 61.10 17.20 4.20 17.10 0.30 0.10 - 0 40 500 480 6 25
Example 19 58.96 17.30 6.51 17.20 0.03 0.00 - 0 40 500 480 6 25
Example 20 55.78 17.50 6.52 20.00 0.10 0.10 - 0 42 500 480 6 25
Example 21 45.79 20.50 13.00 20.50 0.10 0.10 Sn:0.01 0.01 43 560 480 6 25
Example 22 46.20 22.90 7.90 22.90 0.10 0.00 - 0 41 510 480 6 25
Example 23 45.20 23.10 8.00 23.30 0.20 0.20 - 0 25 510 480 6 25
Comparative Example 24 45.00 22.50 7.80 22.50 2.20 0.00 - 0 42 510 480 6 25
Comparative Example 25 45.90 22.90 8.10 23.00 0.00 0.10 - 0 53 510 480 6 25
Comparative Example 26 44.60 22.40 8.00 22.50 0.20 2.30 - 0 42 510 480 6 25
Comparative Example 27 34.90 25.80 14.00 25.10 0.20 0.00 - 0 43 510 480 6 25
Example 30 40.60 25.60 8.00 25.60 0.10 0.10 - 0 44 510 480 6 25
Example 31 45.80 25.70 3.00 25.30 0.10 0.10 - 0 28 550 480 6 25
Example 32 36.40 28.30 7.00 28.10 0.10 0.10 - 0 29 510 480 6 25
Example 33 29.80 30.10 10.00 29.90 0.10 0.10 - 0 50 530 480 6 25
Example 34 17.90 35.00 10.00 35.00 0.10 2.00 - 0 41 540 480 6 25
Comparative Example 35 20.80 36.00 7.00 36.00 0.20 0.00 - 0 25 580 480 8 25
Comparative Example 36 43.2 8.00 4.00 33.00 0.10 0.00 - 0 42 500 660 13 10
- 25 -
[0069]

The base steel sheet was cut into 100 mm x 200 mm and subsequently was
plated using a batch type hot-dip plating test apparatus. The sheet temperature was
measured using a thermocouple spot-welded to a central part of the base steel sheet.
Before dipping in the plating bath, in a furnace having an oxygen concentration
of 20 ppm or lower, the base steel sheet surface was heated and reduced at 860°C in an
atmosphere of N2-S% H2 gas and a dew point of 0°C. Next, the base steel sheet was
air-cooled with N2 gas such that the dipped sheet temperature reached the bath
temperature + 20°C, and was dipped in the plating bath having a bath temperature
shown in Table 1 for about 3 seconds.
After dipping in the plating bath, the base steel sheet was pulled at a pulling
rate of 100 mm/sec to 500 mm/sec. During pulling, the plating adhesion amount was
controlled by N2 wiping gas.
[0070]

After controlling the plating adhesion amount with the wiping gas, the alloying
process was performed on the plated steel sheet under conditions of an alloying
temperature and an alloying time shown in Table 1. In the alloying process, an
induction heating device was used.
[0071]

The plated steel sheet was cooled from the alloying temperature to 335°C by
being cooled in the cooling temperature range under conditions shown in Table 1.
[0072]
- 26 -

In order to investigate the structure configuration of the plating layer, the
prepared sample was cut into 25 (c) x 25 (L) mm, and a surface SEM image of the
plating layer and an element distribution image by EDS were obtained. Regarding the
area fractions of the constituent structures of the plating layer, that is, the Fe-Al phase,
the rod-like lamellar structure of Zn and MgZn2, the massive MgZn2 phase, the Al-Zn
dendrite, the Zn/ Al/MgZn2 ternary eutectic structure, the massive Zn phase, the platelike
Zn/MgZn2lamellar structure, the Fe-Zn phase, the Mg2Si phase, and the other
intermetallic compound phase, one visual field was imaged from each of five samples
having different surface EDS mapping images of the plating layers, that is, five visual
fields (magnification: 1500-fold) in total were imaged, and the area fraction of each of
the structures was measured by image analysis. The area of each of the visual fields
was 45 ~m x 60 ~m. A specific measurement method is as described above.
The area fraction of each of the structures in each of Examples and
Comparative Examples is shown in Table 2.
[0073]

In each of Examples and Comparative Examples, the chemical convertibility
was evaluated using the following method.
The plated steel sheet according to each of Examples and Comparative
Examples manufactured using the above-described method was cut into a size of 50 mm
x 100 mm, and a zinc phosphating process (SD5350 system, manufactured by Nippon
Paint Surf Chemicals Co., Ltd.) was performed thereon.
Regarding the plated steel sheet on which the zinc phosphating process was
performed, the coverage of the chemical conversion crystal was evaluated by SEM
- 27 -
observation. A case where coverage of the chemical conversion crystal was 100%
with respect to the area of the surface was evaluated as "AAA", a case where coverage
of the chemical conversion crystal was 98% or more with respect to the area of the
surface was evaluated as "AA", a case where coverage of the chemical conversion
crystal was 95% or more with respect to the area of the surface was evaluated as "A", a
case where coverage of the chemical conversion crystal was less than 95% and 90% or
more with respect to the area of the surface was evaluated as "B", a case where
coverage of the chemical conversion crystal was less than 90% and 85% or more with
respect to the area of the surface was evaluated as "C", and a case where coverage of the
chemical conversion crystal was less than 85% with respect to the area of the surface
was evaluated as "D". "A" or higher was an acceptable level.
- 28 -
[0074]
[Table 2]
Surface Structure Configuration Evaluation
Rod-Like Massive MgZn2 Fe-Al (A) Plate-Like (B) Massive (C) (Al-Zn) (D) Zn/Al/MgZn2 (E) Mg2Si (F) Other Sum of
Classification No. Zn/MgZn2 Zn/MgZn2 Ternary Eutectic Intermetallic (A) to
Lamellar Structure Phase Phase amellar Structure Zn Phase Dendrite Structure Phase Compound Phase (F) Chemical
Area Fraction Area Fraction Area Area Fraction Area Area Fraction Area Fraction Area Convertibility
(area%) (area%) Fraction (area%) Fraction (area%) (area%) Fraction (area%) (area%)
(area%) (area%) (area%)
Comparative Example 1 Excessive Dross Adhesion c
Comparative Example 2 67 8 9 0 16 0 0 0 0 16 B
Example 3 82 10 0 0 8 0 0 0 0 8 A
Example 4 63 31 4 0 0 2 0 0 0 2 AAA
Example 5 46 49 5 0 0 0 0 0 0 0 AAA
Example 6 29 65 6 0 0 0 0 0 0 0 AA
Comparative Example 7 15 54 31 0 0 0 0 0 0 0 c
Comparative Example 8 0 57 5 38 0 0 0 0 0 38 B
Example 9 65 25 7 0 3 0 0 0 0 3 A
Example 10 49 51 0 0 0 0 0 0 0 0 AAA
Example 11 39 56 5 0 0 0 0 0 0 0 AAA
Example 12 38 52 8 0 0 0 0 2 0 2 AAA
Comparative Example 13 0 51 0 0 0 36 13 0 0 49 c
Comparative Example 14 0 49 0 0 0 37 14 0 0 51 c
Comparative Example 15 12 51 37 0 0 0 0 0 0 0 c
Comparative Example 16 0 53 7 21 0 0 19 0 0 40 B
Example 17 70 21 7 0 0 0 2 0 0 2 AAA
Example 18 46 45 8 0 0 0 0 1 0 1 AAA
Example 19 36 55 9 0 0 0 0 0 0 0 AAA
Example 20 31 59 10 0 0 0 0 0 0 0 AAA
Example 21 9 70 21 0 0 0 0 0 0 0 A
Example 22 25 59 16 0 0 0 0 0 0 0 AA
Example 23 21 61 18 0 0 0 0 0 0 0 AA
Comparative Example 24 19 64 5 0 0 0 0 0 12 12 B
Comparative Example 25 2 55 5 38 0 0 0 0 0 38 B
Comparative Example 26 0 51 0 0 0 21 16 12 0 49 c
Comparative Example 27 4 82 14 0 0 0 0 0 0 0 B
Example 30 14 66 20 0 0 0 0 0 0 0 A
Example 31 48 31 21 0 0 0 0 0 0 0 A
Example 32 9 66 25 0 0 0 0 0 0 0 A
Example 33 6 66 28 0 0 0 0 0 0 0 A
Example 34 5 57 30 0 0 0 0 8 0 8 A
Comparative Example 35 5 60 35 0 0 0 0 0 0 0 c
Comparative Example 36 0 36 29 0 0 0 0 0 35 35 c
- 29 -
[0075]
It was found that, in each of Examples prepared with the predetermined plating
bath composition under the appropriate alloying process conditions and cooling
conditions, the predetermined structures were able to be obtained such that suitable
chemical convertibility was obtained.
On the other hand, at a level (Comparative Example 1) where Aland Fe were
insufficient, dross was excessively attached to the plated steel sheet, and chemical
convertibility deteriorated significantly. At a level (Comparative Example 2) where
the amount of Mg was insufficient, a sufficient amount of the massive MgZn2 phase was
not able to be formed, the structure of the remainder deteriorating chemical
convertibility was excessively formed (the sum of the area fractions ((A) to (F)) exceed
10.0%), and the performance was poor.
[0076]
At a level (Comparative Example 7) where the alloying time was excessively
long, the structure of the Fe-Al phase was excessively formed, and the performance was
poor. At a level (Comparative Examples 8 and 25) where Ca was not added, the
Zn/MgZn2 rod-like lamellar structure was not able to be formed, or only a small amount
thereof was able to be formed. The structure of the remainder was excessively formed,
and the performance was poor.
[0077]
At a level where the alloying temperature was excessively low (Comparative
Example 13) and at a level (Comparative Example 14) where the alloying process was
not performed and the Zn/MgZn2 rod-like lamellar structure was not to be formed, the
structure of the remainder was excessively formed, and the performance was poor. At
a level (Comparative Example 15) where the alloying temperature was excessively high,
- 30 -
the structure of the Fe-Al phase was excessively formed, and the performance was poor.
At a level (comparative Example 36) where the alloying temperature was excessively
high, the alloying time was excessively long, and the cooling rate was slow, the rod-like
Zn/MgZn2lamellar structure was not formed, the Fe-Zn phase was excessively formed
(the Fe-Zn phase was counted as the other intermetallic compound phase), and the
performance was poor. At a level (Comparative Example 16) where the cooling rate
was slow, the rod-like Zn/MgZn2 lamellar structure was not formed, the structure of the
remainder was excessively formed, and the performance was poor.
[0078]
At a level (Comparative Example 24) where an excess amount of Ca was
contained, the structure of the remainder was excessively formed, and the performance
was poor. At a level (Comparative Example 26) where Si is excessively contained,
alloying is inhibited, the rod -like Zn/MgZn2 lamellar structure was not formed, the
structure of the remainder was excessively formed, and the performance was poor.
[0079]
At a level (Comparative Example 27) where an excess amount of Mg was
contained, the rod-like Zn/MgZn2lamellar structure was not formed sufficiently, the
massive MgZn2 phase was excessively formed, and the performance was poor. At a
level (Comparative Example 35) where Aland Fe were excessively contained, the Fe-Al
phase was excessively formed, and the performance was poor.
[0080]
[Example 2]
In Example 2, LME resistance was investigated for Examples which were used
in Example 1. That is, the components, the structures, and the manufacturing
conditions of the plated steel sheets used in Example 2 are shown in Table 1.
- 31 -
[0081]

Some of the plated steel sheets according to Examples used in Example 1 were
cut into a size of 200 mm x 20 mm and were provided for a hot V-bending test to
perform hot V-bending at 800°C. By observing a cross section of the processed
portion after V-bending, whether or not LME cracking occurred was determined to
evaluate LME resistance. A case where LME cracking did not occur in a V-bending
mold having an angle of goo even when R was 6 mm was represented by "AAA", a case
where LME cracking did not occur in a V-bending mold having an angle of goo even
when R was 8 mm was represented by "AA", and a case where LME cracking did not
occur in a V-bending mold having an angle of goo even when R was 16 mm was
represented by "A". "A" or higher was an acceptable level.
The evaluation results of LME resistance of Examples are shown in Table 3.
The area fraction of each of the structures is shown in Table 2 and thus is not shown in
Table 3.
- 32 -
[0082]
[Table 3]
Classification
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
[0083]
No.
3
4
5
6
9
10
11
12
17
18
19
20
21
22
23
30
31
32
33
34
Evaluation
LME Resistance
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AAA
A
AA
AAA
AAA
AAA
AAA
AAA
As shown in Table 3, in each of Examples, LME resistance was suitable. In
particular, in Examples where 30% or more of the rod-like Zn/MgZn2lamellar structure
- 33 -
was present, LME resistance tended to be "AA". In addition, in Examples where 20%
or more of the Fe-Al phase was present, LME resistance was "AAA". When LME
resistance was evaluated for Comparative Examples, LME resistance was evaluated as
B or lower in all Comparative Examples.
[Brief Description of the Reference Symbols]
[0084]
10: plated steel sheet according to embodiment
11: rod-like lamellar structure of Zn and MgZn2
12: massive MgZn2 phase
13: Fe-Al phase
14: Al-Zn dendrite
15: massive Zn
16: Fe-Al phase
17: Mg2Si phase
18: massive MgZn2 phase (that is not hexagonal).

WE CLAIMS

1. A plated steel sheet comprising:
a steel; and
a plating layer that is provided on a surface of the steel,
wherein the plating layer includes, by mass%,
Al: 5.00% to 35.00%,
Mg: 2.50% to 13.00%,
Fe: 5.00% to 35.00%,
Si: 0% to 2.00%,
Ca: 0.03% to 2.00%, and
a remainder consisting of Zn and impurities, and
in a surface of the plating layer, an area fraction of a Fe-Al phase is 0% to 30%,
an area fraction of a rod-like lamellar structure of Zn and MgZn2 is 5% to 90%, an area
fraction of a massive MgZn2 phase is 10% to 70%, and an area fraction of a remainder
is 10% or less.
2. The plated steel sheet according to claim 1,
wherein the plating layer includes, by mass%, Al: 10.00% to 30.00%.
3. The plated steel sheet according to claim 1 or 2,
wherein the plating layer includes, by mass%, Mg: 3.00% to 10.00%.
4. The plated steel sheet according to any one of claims 1 to 3,
wherein the plating layer includes, by mass%, Mg: 4.00% or more.
5. The plated steel sheet according to any one of claims 1 to 4,
wherein the plating layer includes, by mass%, Ca: 0.03% to 1.00%.
6. The plated steel sheet according to any one of claims 1 to 5,
- 35 -
wherein in the surface of the plating layer, an area fraction of the lamellar
structure is 10% to 60%.
7. The plated steel sheet according to any one of claims 1 to 6,
wherein in the surface of the plating layer, an area fraction of an Al-Zn dendrite
mainly formed of anAl phase and a Zn phase is 5% or less.
8. The plated steel sheet according to any one of claims 1 to 7,
wherein in the surface of the plating layer, an area fraction of a Zn/ Al/MgZn2
ternary eutectic structure is 5% or less.
9. The plated steel sheet according to any one of claims 1 to 8,
wherein in the surface of the plating layer, an area fraction of a massive Zn
phase is 10% or less.
10. The plated steel sheet according to any one of claims 1 to 9,
wherein in the surface of the plating layer, an area fraction of a plate-like
Zn/MgZn2lamellar structure is 10% or less.
11. The plated steel sheet according to any one of claims 1 to 10,
wherein in the surface of the plating layer, an area fraction of a Mg2Si phase is
10% or less.