Zinc-based cladding steel plate

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/CN2023/131308 filed on Nov. 13, 2023, which claims priority to Chinese patent application No. 202311409499.7 filed on Oct. 27, 2023. The disclosures of the above-referenced applications are hereby incorporated by reference in their entirety.

BACKGROUND

A steel plate, in order to achieve necessary mechanical properties and surface properties thereof, is inevitable to be added some chemical elements therein or to be performed a surface treatment thereon, but some chemical elements will affect a welding performance of the steel plate. For example, a zinc-based coating can be formed on a surface of the steel plate to prevent surface oxidation and decarburization during a heating process, without subsequent shot peening. The zinc-based coating can also provide sacrificial anode protection and improve an anti-corrosion performance of the zinc-based coating steel plate after being painted.

However, during a welding and especially during a resistance spot welding process, the zinc-based coating steel plate with a lower melting point melts at a higher welding temperature. Under an action of a mechanical tensile stress applied on the steel plate by an electrode which clamps on the steel plate, or a thermal stress generated from thermal expansion and contraction of the steel plate, a molten liquid zinc penetrates into grain boundaries of a base material for the zinc-based coating steel plate, to embrittle the grain boundaries and cause cracks, resulting in a liquid metal embrittlement (LME) crack of the zinc-based coating steel plate induced by a liquid zinc, which seriously restricts an application of the zinc-based coating steel plate.

It should be noted that an information disclosed in the above portion of the Background is only used to enhance an understanding of the background of the disclosure, and therefore may include information that does not constitute the existing technology known to those skilled in the art.

SUMMARY

The disclosure relates to the technical field of a coating steel plate, and in particular to a zinc-based coating steel plate.

The technical problem that a zinc-based coating steel plate is prone to a liquid metal embrittlement crack during welding is solved by utilizing one or more embodiments of the disclosure.

A zinc-based coating steel plate provided according to an embodiment of the disclosure includes at least a base plate layer, an oxide layer adjoined to the base plate layer, and a zinc-based coating adjoined to the oxide layer, the oxide layer including a grain boundary silicon oxide and/or an intracrystalline silicon oxide therein, a thickness of the oxide layer ranging from 3 μm to 10 μm, a mass fraction of the grain boundary silicon oxide in the oxide layer being greater than or equal to 4%.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solution in the examples of the present disclosure, the following will be a brief introduction to accompanying drawings required in the description of the example. Obviously, the drawings described below are some examples of the present disclosure. For those of ordinary skill in the art, other accompanying drawings may be obtained according to those drawings without creative effort.

FIG. 1 shows a schematic structural diagram of a cross-section of a zinc-based coating steel plate according to Embodiment 3 of the disclosure;

FIG. 2 shows a microstructure photograph of a cross-section near a zinc-based coating of the zinc-based coating steel plate according to Example 3 of the disclosure;

FIG. 3 shows a microstructure photograph of a local portion of the oxide layer in the zinc-based coating steel plate according to Example 3 of the disclosure;

FIG. 4 shows a schematic diagram of a distribution of iron of an inhibition layer in the zinc-based coating steel plate according to Example 3 of the disclosure;

FIG. 5 shows a schematic diagram of a distribution of aluminum of an inhibition layer in the zinc-based coating steel plate according to Example 3 of the disclosure;

FIG. 6 shows a microstructure photograph of the zinc-based coating steel plate according to Example 3 of the disclosure;

FIG. 7 shows a microstructure photograph of a cross-section near a zinc-based coating of a zinc-based coating steel plate according to Comparative Example 1 of the disclosure;

FIG. 8 shows a microstructure photograph of a cross-section near a zinc-based coating of a zinc-based coating steel plate according to Comparative Example 2 of the disclosure;

FIG. 9 shows a microstructure photograph of a local portion of the oxide layer of the zinc-based coating steel plate according to Comparative Example 2 of the disclosure;

FIG. 10 shows a partial schematic diagram of an edge portion of a cross-section of a welding spot of the zinc-based coating steel plate according to Embodiment 3 of the disclosure;

FIG. 11 shows a partial schematic diagram of an edge portion of a cross-section of a welding spot of the zinc-based coating steel plate according to Comparative Example 1 of the disclosure; and

FIG. 12 shows a partial schematic diagram of an edge portion of a cross-section of a welding spot of the zinc-based coating steel plate according to Comparative Example 2 of the disclosure.

In the drawings, corresponding relationships between reference signs and component names are as follows:

• • 1, base plate layer; 2, oxide layer; 3, inhibition layer; 4, zinc-based coating.

DETAILED DESCRIPTION

In order to make the purposes, technical solutions and advantages of the embodiments of the disclosure clearer, the technical solutions in the embodiments of the disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the disclosure. Obviously, the described embodiments are only a portion of embodiments of the disclosure, not all the embodiments. Based on the embodiments in the disclosure, all other embodiments obtained by those skilled in the art without any creative efforts fall within the scope of protection sought by the disclosure.

Steel plate is extremely widely applied. For example, in an automobile manufacturing industry, a lightweight of automobiles is an effective way to reduce fuel consumption of automobiles and achieve a goal of carbon emission reduction.

To achieve a goal of lightweight of automobiles while meet requirements of safety regulations for automobiles, an application and development of steel plate on bodies of automobiles have attracted great attention in the industry. For example, in order to ensure a normal use of automobiles in corrosive environments, a surface of steel plate may be galvanized to form a zinc-based coating on the surface of steel plate, and a corrosion resistance of steel plate is improved by the zinc-based coating.

When a steel plate is used to prepare automobile bodies, welding processes can be used for assembly, among which a resistance spot welding is a welding process that is commonly used in assembly processes for automobile bodies. However, a relatively high temperature will be generated in the process of a resistance spot welding. The zinc with a lower melting point in the zinc-based coating may melt at high temperatures. Under an action of a mechanical tensile stress applied on the steel plate by an electrode which clamps on the steel plate, or a thermal stress generated from thermal expansion and contraction of the steel plate, a molten liquid zinc penetrates into grain boundaries of a base material for the zinc-based coating steel plate, to embrittle the grain boundaries and cause cracks, resulting in a liquid metal embrittlement (LME) crack induced by a liquid zinc of the zinc-based coating steel plate, which seriously restricts an application of the zinc-based coating steel plate.

For a problem that the zinc-based coating steel plate in some implementations is prone to the LME crack under an action of liquid zinc, a zinc-based coating steel plate is provided according to an embodiment of the disclosure, referring to FIG. 1 which shows a schematic structural diagram of a cross-section of a zinc-based coating steel plate according to Embodiment 3 of the disclosure. The zinc-based coating steel plate at least includes a base plate layer, an oxide layer adjoined to the base plate layer, and a zinc-based coating adjoined to the oxide layer. The oxide layer includes a grain boundary silicon oxide and/or an intracrystalline silicon oxide therein.

It should be noted that, in the disclosure, silicon is used interchangeably with a chemical symbol Si and has a same meaning as that of the chemical symbol Si.

In some embodiments of the disclosure, an oxide layer is provided in the zinc-based coating steel plate, and includes a grain boundary silicon oxide and/or an intracrystalline silicon oxide, that is, a silicon oxide may be enriched in the oxide layer, and can block a liquid zinc from penetrating into the base plate layer to a certain extent, thereby solving the LME crack to a certain extent.

During the welding process, the grain boundary silicon oxide and/or intracrystalline silicon oxide in the oxide layer can block a penetration of the liquid zinc into the base plate layer, and can avoid an occurrence of the LME crack caused by the liquid zinc to a certain extent.

In some embodiments, Referring to FIGS. 2 and 3. FIG. 2 shows a microstructure photograph of a cross-section near a zinc-based coating of the zinc-based coating steel plate according to Example 3 of the disclosure. FIG. 3 shows a microstructure photograph of a local portion of the oxide layer in the zinc-based coating steel plate according to Example 3 of the disclosure. It can be seen from FIG. 2 and FIG. 3 that the oxide layer is adjoined to the base plate layer and is located on a surface of the base plate layer.

In some embodiments, the oxide layer may include only a grain boundary silicon oxide. In other embodiments, the oxide layer may include only an intracrystalline silicon oxide. In other embodiments, the oxide layer may include both a grain boundary silicon oxide and an intracrystalline silicon oxide.

In some embodiments, a silicon oxide may be selected from any one or more of SiO, SiO₂, and Si₂O₆.

As an optional embodiment, a thickness of the oxide layer is 3 μm˜10 μm.

In some embodiments, a liquid zinc can be more effectively prevented from penetrating into the base plate layer by controlling the thickness of the oxide layer to range from 3 μm to 10 μm, thereby more effectively suppressing an occurrence of LME crack without significantly affecting material properties of the base plate layer.

In some embodiments, if the thickness of the oxide layer is too large, material properties of the base plate layer may be affected to a certain extent; if the thickness of the oxide layer is too small, an inhibitory effect of the oxide layer on the LME crack may be affected to a certain extent. In some embodiments, the thickness of the oxide layer may be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any other thickness value within a range of 3 μm to 10 μm.

As an optional embodiment, a mass fraction of the grain boundary silicon oxide in the oxide layer is greater than or equal to 4%.

In some embodiments, a mass fraction of the grain boundary silicon oxide in the oxide layer is greater than or equal to 4%, so that the silicon oxide can occupy a position along a grain boundary to block a penetration channel of a liquid zinc, thereby inhibiting the liquid zinc from penetrating into the base plate layer. If a content of silicon oxide at the grain boundary in the oxide layer is too low, it may be difficult to effectively block the penetration channel of the liquid zinc to a certain extent, thereby reducing an effect of hindering the penetration of the liquid zinc.

In some embodiments, a mass fraction of the grain boundary silicon oxide in the oxide layer may be 4%, 4.5%, 5%, 5.5%, 6%, etc.

As an optional embodiment, the mass fraction of the grain boundary silicon oxide in the oxide layer is 5.0% to 6.4%.

As an optional embodiment, a mass fraction of the intracrystalline silicon oxide in the oxide layer is greater than or equal to 1%, and a ratio of the mass fraction of the intracrystalline silicon oxide in the oxide layer to the mass fraction of the grain boundary silicon oxide in the oxide layer is less than 1:2.

In some embodiments, by controlling the mass fraction of the intracrystalline silicon oxide in the oxide layer to be greater than or equal to 1%, and a ratio of the mass fraction of the intracrystalline silicon oxide in the oxide layer to the mass fraction of the grain boundary silicon oxide in the oxide layer to be less than 1:2, a silicon oxide which occupies an intracrystalline position can reduce an infiltration performance of the liquid zinc to inhibit the penetration of the liquid zinc into the base plate layer. If the mass fraction of the intracrystalline silicon oxide in the oxide layer is too low, the intracrystalline silicon oxide in the oxide layer has a poor effect of reducing the infiltration performance of the liquid zinc, and the intracrystalline silicon oxide in the oxide layer has a non obvious effect of inhibiting the penetration of the liquid zinc into the base plate layer. If the ratio of the mass fraction of the intracrystalline silicon oxide in the oxide layer to the mass fraction of the grain boundary silicon oxide in the oxide layer is too large, then under an action of the intracrystalline silicon oxide on reducing the infiltration performance of the liquid zinc, a preparation of the zinc-based coating will be affected to a certain extent, thereby affecting a quality of the zinc-based coating, and resulting in a risk of surface dezincification of the zinc-based coating.

In some embodiments, the mass fraction of the intracrystalline silicon oxide in the oxide layer may be 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 2% or the like. A ratio of the mass fraction of the intracrystalline silicon oxide in the oxide layer to the mass fraction of the grain boundary silicon oxide in the oxide layer may be 1:2, 1:2.5, 1:3, 1:3.5, 1:4 and 1:5 or the like.

As an optional embodiment, the mass fraction of the intracrystalline silicon oxide in the oxide layer is 1.0%-2.0%.

In some embodiments, a Scanning Electron Microscope (SEM) and an Energy Dispersive Spectrometer (EDS) may be used to detect contents of the grain boundary silicon oxide and the intracrystalline silicon oxide in the oxide layer. For example, for an oxide layer shown in FIG. 3 upon tested, a mass fraction of the grain boundary silicon oxide ranges from 5.0% to 6.4%, and a mass fraction of the intracrystalline silicon oxide ranges from 1.0% to 2.0%.

It should be noted that in the embodiments of the disclosure, the mass fraction of the grain boundary silicon oxide refers to a percentage of a total mass of the grain boundary silicon oxide in the oxide layer to an overall mass of the oxide layer. The mass fraction of the intracrystalline silicon oxide refers to a percentage of a total mass of the intracrystalline silicon oxide in the oxide layer to the overall mass of the oxide layer.

As an optional embodiment, the zinc-based coating steel plate further includes an inhibition layer adjoined between the oxide layer and the zinc-based coating. A thickness of the inhibition layer is less than or equal to 2 μm.

In some embodiments, the zinc-based coating steel plate further includes an inhibition layer located between the oxide layer and the zinc-based coating, and a thickness of the inhibition layer is controlled as below 2 μm. The inhibition layer can inhibit a generation of LME crack without increasing manufacturing difficulty and manufacturing cost. In addition, the thickness of the inhibition layer does not need to be too large. If the thickness of the inhibition layer is too large, it will not only increase the manufacturing difficulty and manufacturing cost of the zinc-based coating steel plate to a certain extent, but also have no significant increase in an inhibitory effect on LME crack.

In some embodiments, the thickness of the inhibition layer may be less than or equal to 2 μm, for example 2 μm, 1.8 μm, 1.6 μm, 1.4 μm or the like.

As an optional embodiment, the inhibition layer includes at least iron and zinc therein. Optionally, the inhibition layer also includes aluminum therein.

In some embodiments, the iron and aluminum in the inhibition layer may form an iron-aluminum (Fe-Al) compound, which overall serves to hinder an alloying reaction between the zinc-based coating and the base plate layer, to inhibit the generation of LME crack.

In some embodiments, an electron probe may be used to detect a distribution of elements in the inhibition layer, as shown in FIGS. 4 and 5. FIG. 4 shows a schematic diagram of a distribution of iron of an inhibition layer in the zinc-based coating steel plate according to Example 3 of the disclosure, and FIG. 5 shows a schematic diagram of a distribution of aluminum of an inhibition layer in the zinc-based coating steel plate according to Example 3 of the disclosure.

As an optional embodiment, the zinc-based coating includes a pure zinc coating and/or a zinc alloy coating. The zinc alloy coating includes zinc, and the zinc alloy coating also includes at least one of iron, aluminum, magnesium and nickel. Contents of iron, aluminum, magnesium, nickel and zinc in the zinc alloy coating are as follows in mass fractions:

• • a content of iron is 0.0˜15.0%;
  • a content of aluminum is 0.0˜60.0%;
  • a content of magnesium is 0.0˜4.0%;
  • a content of nickel is 0.0˜20.0%;
  • the rest is zinc.

In some embodiments, the zinc-based coating is mainly used to protect a steel plate from corrosion, thereby ensuring that an apparatus using the zinc-based coating steel plate can be used normally in a corrosive environment. For example, the zinc-based coating can ensure a normal use of an automobile in a corrosive environment with a certain humidity and ensure a service life of the automobile.

In some embodiments, the zinc-based coating steel plate may be annealed galvanized by using pure zinc to form a pure zinc coating.

In some embodiments, the zinc-based coating steel plate may be annealed and galvanized by using an alloy containing zinc to form a zinc alloy coating. That is, the zinc alloy coating may contain at least one of iron, aluminum, magnesium and nickel in addition to zinc.

In some embodiments, the zinc-based coating may also include a pure zinc coating and a zinc alloy coating.

In some embodiments, a thickness of the zinc-based coating may be 5 μm to 15 μm. For example, the thickness of the zinc-based coating is 5 μm, 6 μm, 7 μm, 9 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm and the like.

In some embodiments, when the zinc-based coating is a pure zinc coating, an inhibition layer may be disposed between the pure zinc coating and the oxide layer. The inhibition layer may hinder an alloying reaction between the pure zinc coating and an iron base body (the oxide layer and/or the base plate layer may be regarded as the iron base body) at high temperature, to inhibit the generation of LME crack.

As an optional embodiment, contents of iron, aluminum, magnesium, nickel and zinc in the zinc alloy coating are as follows in mass fractions:

• • a content of iron is 5.0%˜15.0%;
  • a content of aluminum is 1.0%˜60.0%;
  • a content of magnesium is 0.5%˜4.0%;
  • a content of nickel is 8.0%˜20.0%; and
  • the rest are zinc and unavoidable impurities.

As an optional embodiment, the base plate layer includes iron, carbon, manganese and silicon, and also includes at least one of aluminum, chromium, molybdenum, niobium, titanium and boron. Contents of iron, carbon, manganese, silicon, aluminum, chromium, molybdenum, niobium, titanium and boron in the base plate layer are as follows in mass fractions:

• • a content of carbon is 0.05%˜1.00%;
  • a content of manganese is 1.20%˜3.00%;
  • a content of silicon is 0.10%˜3.00%;
  • a content of aluminum is 0.00˜1.00%;
  • a content of chromium is 0.00˜0.60%;
  • a content of molybdenum is 0.00˜0.60%;
  • a content of niobium is 0.00˜0.10%;
  • a content of titanium is 0.00˜0.10%;
  • a content of boron is 0.0000˜0.0025%; and
  • the rest are iron and unavoidable impurities.

In some embodiments, contents of compositions included in the base plate layer are as follows in mass fractions:

• • a content of carbon is 0.15%˜0.25%;
  • a content of manganese is 1.70%˜2.80%;
  • a content of silicon is 1.0%˜2.00%; and

the rest are iron and unavoidable impurities.

As an optional embodiment, contents of iron, carbon, manganese, silicon, aluminum, chromium, molybdenum, niobium, titanium and boron included in the base plate layer are as follows in mass fractions:

• • a content of carbon is 0.05%˜1.00%;
  • a content of manganese is 1.20%˜3.00%;
  • a content of silicon is 0.10%˜3.00%;
  • a content of aluminum is 0.02%˜1.00%;
  • a content of chromium is 0.10%˜0.60%;
  • a content of molybdenum is 0.05%˜0.60%;
  • a content of niobium is 0.01%˜0.10%;
  • a content of titanium is 0.01%˜0.10%;
  • a content of boron is 0.0001%˜0.0025%; and
  • the rest are iron and unavoidable impurities.

As an optional embodiment, a microstructure of the base plate layer includes a retained austenite.

In some embodiments, the base plate layer contains the retained austenite, and thus a plasticity of the base plate layer can be increased by using a principle that the retained austenite is transformed into a martensitic structure during deformation of the retained austenite, to meet elongation requirements.

As an optional embodiment, the microstructure of the base plate layer includes a ferrite, and also includes at least one of a pearlite, a bainite and a martensite.

In some embodiments, the ferrite in the base plate layer can increase the plasticity of the base plate layer to enable the base plate layer to meet the elongation requirements.

In some embodiments, the pearlite, bainite, and martensite in the base plate layer can increase a strength of the base plate layer to meet strength requirements.

In some embodiments of the disclosure, a tensile strength of the zinc-based coating steel plate can reach above 500 MPa.

In some embodiments, the tensile strength of the zinc-based coating steel plate can reach above 800 MPa, while a yield strength of the zinc-based coating steel plate can reach above 600 MPa, and an elongation A80 can reach above 15%, so that the strength and elongation of the zinc-based coating steel plate can meet requirements of automotive structural components on which the zinc-based coating steel plate is applied.

For example, referring to FIG. 6, which shows a microstructure photograph of the zinc-based coating steel plate according to Example 3 of the disclosure, it can be found from test that the zinc-based coating steel plate of Example 3 has a yield strength ≥650 MPa, a tensile strength ≥1000 MPa, and an elongation A80≥16%.

It should be noted that the high temperature mentioned in the embodiments of the disclosure refers to a temperature at which zinc can be melted and a range of temperatures which are higher than the temperature at which zinc can be melted.

Based on a same inventive concept, the disclosure also proposes a method for preparing the zinc-based coating steel plate, which includes the following steps.

A continuous annealing treatment and a galvanizing treatment are performed in sequence on a cold hard plate to obtain a zinc-based coating steel plate. The continuous annealing treatment includes a pre-oxidation stage, a heating stage and a soaking stage.

In some embodiments, an oxide layer may be formed on a surface of a base plate layer through a continuous annealing treatment, and a surface state of the oxide layer may be improved, so that a zinc-based coating with good adhesion may be obtained during subsequent galvanizing treatment.

As an optional embodiment, before the continuous annealing treatment is performed on the cold hard plate, the following steps may also be included:

A smelting step, a continuous casting step, a hot rolling step, a pickling step and a cold rolling step are performed to obtain the cold hard plate.

As an optional embodiment, in the continuous annealing treatment, a cooling stage may be included after the soaking stage.

As an optional embodiment, a dew point temperature of the pre-oxidation stage ranges from 0° C. to 20° C.

In some embodiments, the dew point temperature of the pre-oxidation stage is controlled to be in a range of 0° C. to 20° C., such that an iron oxide layer can be formed on a surface of the base plate layer, while a silicon is oxidized and enriched at a grain boundary and within grains near the surface of the base plate layer to prepare to form an oxide layer near the surface of the base plate layer. Therefore, the oxide layer may be regarded as a portion of the base plate layer which is adjacent to the surface.

In some embodiments, if the dew point temperature of the pre-oxidation stage is too high, the silicon layer enriched near the surface of the base plate layer will be thickened to a certain extent, that is, the oxide layer formed through the heating stage and the soaking stage will be thickened, resulting in that mechanical properties of the zinc-based coating steel plate will be affected and an adverse effect will be generated on the mechanical properties of the zinc-based coating steel plate. If the dew point temperature of the pre-oxidation stage is too low, a formation of the iron oxide layer on the surface of the base plate layer in the pre-oxidation stage will be affected to a certain extent, which will be not conducive to a formation of the inhibition layer in later stages.

In some embodiments, the dew point temperature of the pre-oxidation stage may be 0° C., 4° C., 8° C., 12° C., 16° C., 20° C., etc.; alternatively, the dew point temperature of the pre-oxidation stage may be 5° C. to 10° C.

As an optional embodiment, the dew point temperature of the heating stage ranges from −32° C. to −25° C.; and the dew point temperature of the soaking stage ranges from −32° C. to −25° C.

In some embodiments, the dew point temperatures of the heating stage and the soaking stage are controlled to be both within a range of−32° C. to −25° C., such that the iron oxide formed on the surface of the base plate layer can be reduced to form a thinner iron reduction layer on the surface of the base plate layer. Therefore, the iron reduction layer can be regarded as a portion of the base plate layer located on the surface. The iron reduction layer can improve a platability of the surface of the base plate layer to improve an adhesion of the zinc-based plating layer. At the same time, in the heating stage and the soaking stage, a silicon as an oxygen-affinity element, which is enriched at the grain boundaries and in the grains near the surface of the base plate layer, will continue to be oxidized, thereby forming an oxide layer that satisfies requirements for contents of the silicon oxide. In addition, the iron reduction layer on a surface of the base plate layer can form an iron-aluminum compound as an inhibition layer with the aluminum in materials for galvanizing during a galvanizing process to ensure a quality of the zinc-based coating and improve an adhesion of the zinc-based coating.

In some embodiments, if the dew point temperature of the heating stage or the soaking stage is too high, the iron oxide layer formed in the pre-oxidation stage cannot be reduced to a certain extent, and in turn the quality of the zinc-based coating may be affected. If the dew point temperature of the heating stage or the soaking stage is too low, an oxidation process of silicon during the heating stage or the soaking stage will be affected to a certain extent, resulting in difficulty in forming the oxide layer that can block an intrusion of liquid zinc.

In some embodiments, the dew point temperature of the heating stage may be−32° C., −31° C.,−29° C., −27° C., −25° C. and the like. The dew point temperature of the soaking stage may be −32° C., −31° C., −29° C., −27° C., −25° C. and the like.

The method for preparing the zinc-based coating steel plate in the embodiments of the disclosure is used to prepare the above-mentioned zinc-based coating steel plate. A structure of the zinc-based coating steel plate can refer to the embodiments. Since the method for preparing the zinc-based coating steel plate adopts some or all technical solutions of the above-mentioned embodiments, it has at least all advantageous effects brought by the technical solutions of the embodiments, which will not be repeated here.

The disclosure is further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the disclosure and are not intended to limit the scope of the disclosure. Experimental methods without specifying specific conditions in the following examples are typically performed in accordance with national standards. If there are no corresponding national standards, general international standards, conventional conditions, or conditions recommended by the manufacturer shall be followed.

A zinc-based coating steel plate is provided according to an embodiment of the disclosure, which includes a base plate layer, an oxide layer, an inhibition layer and a zinc-based coating which are adjoined to one another in sequence, the oxide layer including a grain boundary silicon oxide and/or an intracrystalline silicon oxide. Chemical compositions of the base plate layer in the zinc-based coating steel plate are shown in Table 1, and surface property parameters of the zinc-based coating steel plate are shown in Table 2.

TABLE 1
Chemical compositions of base plate layer
in zinc-based coating steel plate

	Mass fraction	Mass fraction	Mass fraction
Serial number	of C (%)	of Mn (%)	of Si (%)

Example 1	0.25	2.8	1.0
Example 2	0.15	1.7	2.0
Example 3	0.2	2.0	1.5
Comparative	0.1	2.2	0.5
Example 1
Comparative	0.2	2.0	0.5
Example 2

TABLE 2
Surface property parameters of zinc-based coating steel plate

	thickness	thickness	mass fraction	mass	ratio of mass fraction of	thickness
	of	of	of grain	fraction of	intracrystalline silicon	of
	oxide	inhibition	boundary	intracrystalline	oxide to mass fraction of	zinc-based
Serial	layer	layer	silicon oxide	silicon	grain boundary silicon	coating
number	(μm)	(μm)	(%)	oxide (%)	oxide	(μm)

Example 1	3	0.5	4	1	1/4	10
Example 2	10	2	8	3	3/8	10
Example 3	5	1	6	2	1/3	10
Comparative	1	0.5	4	0.8	1/5	10
Example 1
Comparative	10	0	3	0.6	1/5	10
Example 2

In some embodiments, a Scanning Electron Microscope (SEM) may be used in combination with an Energy Dispersive Spectrometer (EDS) to detect a distribution situation of the grain boundary silicon oxide and intracrystalline silicon oxide in the zinc-based coating steel plate. FIG. 3 shows a microstructure photograph of a local portion of the oxide layer in the zinc-based coating steel plate according to Example 3 of the disclosure, and FIG. 9 shows a microstructure photograph of a local portion of the oxide layer of the zinc-based coating steel plate according to Comparative Example 2 of the disclosure. Combined with the Energy Dispersive Spectrometer (EDS), the distribution situation of the grain boundary silicon oxide and intracrystalline silicon oxide of Example 3 and Comparative Example 2 are detected and shown in Table 3.

TABLE 3
Distribution of grain boundary silicon oxide and intracrystalline
silicon oxide in zinc-based coating steel plate

			Mass fraction of
		Mass fraction of	silicon oxide of
Oxidation		silicon oxide of	Comparative
position	Spectrum	Example 3 (%)	Example 2 (%)

Grain	Spectrum 1	6.4	0.9
boundary
oxidation
Grain	Spectrum 2	6.2	0.5
boundary
oxidation
Grain	Spectrum 3	5.0	1.4
boundary
oxidation
Grain	Spectrum 4	5.1	2.9
boundary
oxidation
Intracrystalline	Spectrum 5	2.0	0.6
Oxidation
Intracrystalline	Spectrum 6	1.5	0.6
Oxidation
Intracrystalline	Spectrum 7	1.0	0.0
Oxidation

A method for preparing a zinc-based coating steel plate is provided according to an embodiment of the disclosure, including the following steps.

In S11, a continuous annealing treatment and a galvanizing treatment are performed on the cold hard plate to obtain a zinc-based coating steel plate; The continuous annealing treatment includes a pre-oxidation stage, a heating stage and a soaking stage. The dew point temperatures of the pre-oxidation stage, the heating stage and the soaking stage are shown in Table 4, and mechanical properties of the obtained zinc-based coating steel plate are shown in Table 5.

TABLE 4
Dew point temperatures in continuous annealing
treatment for zinc-based coating steel plate

	Dew point	Dew point	Dew point
	temperature of pre-	temperature of	temperature of
Serial	oxidation stage	heating stage	soaking stage
number	(° C.)	(° C.)	(° C.)

Example 1	0	−32	−32
Example 2	20	−25	−25
Example 3	10	−29	−29
Comparative	−10	−40	−40
Example 1
Comparative	0	−35	−35
Example 2

TABLE 5
Mechanical performances of zinc-based coating steel plate

	Yield strength	Tensile strength	Elongation A80
Serial number	(MPa)	(MPa)	(%)

Example 1	600	1000	17
Example 2	760	1000	16
Example 3	700	1000	16.5
Comparative	650	1000	13
Example 1
Comparative	750	1000	17
Example 2

In order to illustrate an effectiveness of the embodiments of the disclosure in reducing the LME crack caused by resistance spot welding, occurrence situations of the LME cracks in resistance spot welded joints of Examples 1-3 and Comparative Examples 1-2 are analyzed. The zinc-based coating steel plates of Examples 1-3 and Comparative Examples 1-2 are resistance spot welded according to welding process parameters for testing LME cracks of the zinc-based coating steel plates shown in Table 6. The welding experiments were carried out based on SEP1220-2 resistance spot welding standard. An upper limit current of each material approaching to expulsion is selected as a welding current. Detection results for the LME cracks of the zinc-based coating steel plate after being welded are shown in Table 7.

TABLE 6
Welding process parameters for testing LME
cracks of zinc-based coating steel plates

Serial number

	Example 1	Example 2	Example 3	Example 1	Example 2

Plate thickness	1.6	mm	1.6	mm	1.6	mm	1.2	mm	1.5	mm
Diameter of	6	mm	6	mm	6	mm	6	mm	6	mm
electrode tip
Electrode force	4.5	kN	4.5	kN	4.5	kN	4.0	kN	4.5	kN
Welding current	7.9	kA	7.9	kA	7.9	kA	7.9	kA	7.9	kA
Welding time	380	ms	380	ms	380	ms	320	ms	380	ms
Holding time of	300	ms	300	ms	300	ms	300	ms	300	ms
electrode force

TABLE 7
Detection results for LME cracks of zinc-based coating steel plates

Serial number	Whether there are obvious LME cracks
Example 1	none
Example 2	none
Example 3	none
Comparative Example 1	yes
Comparative Example 2	yes

FIG. 7 shows a microstructure photograph of a cross-section near a zinc-based coating of a zinc-based coating steel plate according to Comparative Example 1 of the disclosure.

FIG. 8 shows a microstructure photograph of a cross-section near a zinc-based coating of a zinc-based coating steel plate according to Comparative Example 2 of the disclosure. FIG. 9 shows a microstructure photograph of a local portion of the oxide layer of the zinc-based coating steel plate according to Comparative Example 2 of the disclosure. As shown in FIG. 7 to FIG. 9, the oxide layers of Comparative Examples 1 and 2 are different from that of the Example 3.

FIG. 10 shows a partial schematic diagram of an edge portion of a cross-section of a welding spot of the zinc-based coating steel plate according to Embodiment 3 of the disclosure. FIG. 11 shows a partial schematic diagram of an edge portion of a cross-section of a welding spot of the zinc-based coating steel plate according to Comparative Example 1 of the disclosure. FIG. 12 shows a partial schematic diagram of an edge portion of a cross-section of a welding spot of the zinc-based coating steel plate according to Comparative Example 2 of the disclosure. As shown in FIG. 10 to FIG. 12, no obvious LME cracks were observed at the edge portion of the cross-section of the weld point in Example 3 of the disclosure, but obvious LME cracks were observed at the edge portion of the cross-section of the weld point in Comparative Examples 1 and 2. It can be seen that zinc-based coating steel plates, which have oxide layer structures different from that of the embodiments of the disclosure and are prepared by a preparation method different from that of the embodiments of the disclosure, have obvious defects of the LME cracks and pose certain safety hazards, even if mechanical properties thereof are similar to those of the embodiments of the disclosure.

Compared with the comparative examples, the zinc-based coating steel plate of the embodiments of the disclosure is provided with an oxide layer, and the oxide layer includes a grain boundary silicon oxide and/or an intracrystalline silicon oxide, that is, silicon oxides may be enriched in the oxide layer, and the silicon oxides can block a liquid zinc from penetrating into the base plate layer to a certain extent, thereby solving a technical problem of the LME crack to a certain extent.

During the welding process, the grain boundary silicon oxide and/or intracrystalline silicon oxide in the oxide layer can block the penetration of the liquid zinc into the base plate layer, and can avoid an occurrence of LME crack caused by the liquid zinc to a certain extent.

At the same time, an inhibition layer is also provided in the zinc-based coating steel plate, and can also improve the effect of inhibiting the LME crack to a certain extent.

Various embodiments of the disclosure may exist in the form of a range It should be understood that the description in the form of a range is only for convenience and simplicity and should not be understood as a hard limit to the scope of the disclosure; therefore, the described range should be considered to have specifically disclosed all possible subranges as well as the single values within such a range. For example, a description of a range from 1 to 6 should be considered to have specifically disclosed subranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, and from 3 to 6, and a single number within the stated range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it is intended to include any cited number (fractional or whole) within the indicated range.

In the disclosure, “and/or” describes the relationship between associated objects, indicating that there may be three relationships. For example, A and/or B may refer to: A alone, both A and B, and B alone. A and B can be singular or plural. In this document, “at least one” means one or more, and “plurality” means two or more. “At least one”, “at least one of the following” or similar expressions thereof refers to any combination of these items, including single items or any combination of plural items. For example, “at least one of a, b, or c”, or “at least one of a, b, and c” can mean: a, b, c, a˜b (that is, a and b), a˜c, b˜c, or a˜b-c, where a, b, and c can each be single or multiple.

Unless otherwise specified, various raw materials, reagents, instruments and apparatuses used in the disclosure can be purchased from the market or prepared by existing methods.

The above descriptions are only specific embodiments of the disclosure, enabling those skilled in the art to understand or implement the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principle defined herein may be practiced in other embodiments without departing from the spirit or scope of the disclosure. Therefore, the disclosure is not to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features claimed herein.