Welding method for improving plating protrusion of welding spot of zinc-aluminum-magnesium plating steel plate

Abstract

The invention discloses a welding method for improving plating protrusions of welding spots of a zinc-aluminum-magnesium plated steel plate, which comprises the following steps: (1) preparing a zinc-aluminum-magnesium plated steel plate to be welded with the sheet layer thickness of less than 3mm, lapping the zinc-aluminum-magnesium plated steel plate to form a two-layer or three-layer plate group for standby welding, and arranging at least one layer on the outermost layer as the zinc-aluminum-magnesium plated steel plate; (2) scrubbing dirt on the surface of the steel plate by using alcohol before welding until no foreign matter visible to naked eyes exists; and (3) welding is conducted, two-section welding is adopted and comprises a preheating section and a welding section, the preheating section comprises preheating time, preheating current and cooling time, and the welding section comprises welding time, welding current and cooling time. According to the welding method for improving the protrusion of the zinc-aluminum-magnesium coated steel plate welding spot coating, the problem of protrusion of the zinc-aluminum-magnesium coated steel plate welding spot coating and the welding problem easily occurring to a conventional welding spot are solved.

Description

Technical Field

[0001] The invention relates to the field of metallurgical welding, and in particular to a welding method for improving plating protrusions at welding points of zinc-aluminum-magnesium coated steel plates. Background Art

[0002] In the field of automobile body-in-white, the most commonly used materials are pure zinc-plated and zinc-iron alloyed steel plates, which are considered to have good corrosion resistance. With the rapid development of the automobile industry, automobile body-in-white has put forward higher requirements on the corrosion resistance of steel plate coatings. In more complex and harsh environments such as humidity, high heat and high salt, the surface coating of pure zinc-plated and zinc-iron alloyed steel plates has poor corrosion protection effect on the cut of the plate. In order to meet the corrosion resistance requirements of the cut and the entire body, a painting and edge banding process must be added, which not only increases the production cost of the whole vehicle, but also reduces production efficiency. Therefore, it is urgent to develop coating products with higher corrosion resistance that can withstand complex service environments.

[0003] By adding a small amount of Al and Mg elements to pure zinc, a coating product with a Zn-Al-Mg composition system (referred to as low-aluminum zinc aluminum magnesium) was developed. Its corrosion resistance is significantly better than the currently commonly used pure zinc-plated and zinc-iron alloyed steel plates.

[0004] Resistance spot welding technology is widely used in the manufacture of automobile bodies due to its advantages of low cost, high efficiency, easy automation and strong welds. According to statistics, the average number of welds on each car body is not less than 3,000. For zinc-aluminum-magnesium products, their excellent corrosion resistance is brought by the complex component system, and the coating of the complex component system is prone to the simultaneous existence of multiple alloy phases with different melting points. Resistance spot welding is a process of heating melting-cooling solidification, especially in the process of gradual solidification after melting. Due to the complex influence of the various alloy phases contained in the coating on the wettability and fluidity of the coating, the high-temperature zinc liquid is prone to segregation under the interference of factors such as uneven magnetic fields, which eventually leads to the formation of local zinc heaps after the weld solidifies, referred to as weld zinc convex. In the subsequent painting process of the automobile plate, this weld zinc convex defect is constantly magnified, seriously affecting the feel and aesthetics of the visible area of ​​the automobile body-in-white.

[0005] The current zinc-aluminum-magnesium coated steel sheets mainly focus on coating composition, production and manufacturing process, and corrosion resistance. Chinese patent CN118127445A discloses a low-aluminum zinc-aluminum-magnesium coated plate and its preparation method. In order to solve the problem of poor surface quality caused by zinc ash and zinc slag in the production process, a coating with a composition of 1.0% to 1.4% Mg content, 1.5% to 1.9% Al content, and the rest Zn is invented. Chinese patent CN113500278A discloses a welding method for zinc-aluminum-magnesium coated plates. The patent mainly coats powdered metal between two test plates to be welded, matches the preferred resistance spot welding process, and invents a welding method for zinc-aluminum-magnesium coated plates, which meets the requirements of conventional performance such as shear resistance of the weld.

[0006] Therefore, it is necessary to develop a new welding method to reduce the problem of coating protrusion at the weld point of zinc-aluminum-magnesium coated steel sheets. Summary of the invention

[0007] The purpose of the present invention is to provide a welding method for improving the plating protrusions at the weld points of zinc-aluminum-magnesium coated steel plates, which not only improves the plating protrusions at the weld points of zinc-aluminum-magnesium products, but also solves the welding problems that are easy to occur in conventional resistance spot welding welds of zinc-aluminum-magnesium products, such as cold welding, severe spatter and low weld strength.

[0008] The present invention adopts the following technical solutions:

[0009] The present invention provides a welding method for improving the coating protrusion of a zinc-aluminum-magnesium coated steel plate welding point, comprising the following steps:

[0010] (1) preparing zinc-aluminum-magnesium coated steel plates with a sheet thickness of ≤3 mm to be welded, overlapping them into two or three layers of plates for welding, wherein at least one outermost layer is a zinc-aluminum-magnesium coated steel plate;

[0011] (2) Before welding, use alcohol to clean the surface of the steel plate until there is no foreign matter visible to the naked eye;

[0012] (3) Welding: two-stage welding is adopted, including a preheating stage and a welding stage. The preheating stage includes preheating time, preheating current and cooling time, and the welding stage includes welding time, welding current and cooling time.

[0013] In the above technical solution, the two-layer or three-layer plate group can be overlapped by two or three zinc-aluminum-magnesium coated steel plates to be welded, or can be overlapped by the zinc-aluminum-magnesium coated steel plates to be welded and other steel plates.

[0014] Preferably, the components of the zinc-aluminum-magnesium coating, in terms of mass percentage, include: Mg: 1.5% to 3.0%, Al: 1.0% to 1.5%, Si: 0.6 to 0.8%, and the rest is Zn.

[0015] The chemical composition of the coating has an important influence on the melting point of the coating and the fluidity of the zinc liquid. Generally, the higher the melting point of the coating and the worse the fluidity of the zinc liquid after the coating is melted, the less likely the zinc liquid will flow in a certain direction of strong attraction during the welding process.

[0016] The addition of magnesium to zinc liquid usually increases the melting point. The zinc-magnesium alloy formed by magnesium and zinc (such as Zn-Mg alloy) has a high melting point, so the addition of magnesium will increase the melting point of zinc liquid. In addition, the addition of magnesium usually leads to a decrease in the fluidity of zinc liquid. The addition of magnesium increases the viscosity of zinc liquid and reduces its fluidity. Especially in the case of high magnesium content, the structure of zinc-magnesium alloy is relatively strong and the fluidity is significantly reduced. Therefore, in low-aluminum zinc-aluminum-magnesium, the magnesium content should be higher than 1.5% (mass fraction), but not too high.

[0017] The addition of aluminum to zinc liquid usually lowers the melting point. The aluminum-zinc alloy (such as Zn-Al alloy) formed by aluminum and zinc has a lower melting point, which allows the aluminum-containing zinc liquid to melt at a lower temperature. In addition, the addition of aluminum also helps to improve the fluidity of the zinc liquid. Therefore, in low-aluminum zinc aluminum magnesium, it should not be higher than 1.5% (mass fraction), but it should not be lower than 1.0% (mass fraction) to ensure corrosion resistance.

[0018] Silicon has a relatively low melting point in zinc liquid, and the addition of a small amount of silicon can usually lower the melting point of zinc liquid. Silicon has a relatively low melting point in zinc liquid, and the addition of a small amount of silicon can usually lower the melting point of zinc liquid. The addition of silicon usually increases the viscosity of zinc liquid, resulting in a decrease in fluidity. The alloy or compound formed by silicon and zinc usually has a strong crystal structure, which enhances the internal friction of zinc liquid and inhibits fluidity. However, at a low content of silicon (such as below 0.5% (mass fraction)), fluidity can be improved. Therefore, the silicon content should not be lower than 0.6% (mass fraction), but in order not to significantly reduce the melting point of zinc liquid, the silicon content should not be higher than 0.8% (mass fraction).

[0019] Preferably, the single-piece thickness of the zinc-aluminum-magnesium coated steel plate to be welded is ≤1 mm.

[0020] Preferably, the weight of the zinc-aluminum-magnesium coating does not exceed 50 g / m 2 .

[0021] More preferably, the weight of the zinc-aluminum-magnesium coating is 42-50 g / m 2 .

[0022] More preferably, the weight of the zinc-aluminum-magnesium coating is 42-45 g / m 2 .

[0023] Preferably, the preheating current is 10-14 kA.

[0024] Preferably, the welding time is not shorter than 500 ms.

[0025] Other welding parameters except welding current (such as welding pressure, etc.) are selected according to the material type and thickness of the plate group.

[0026] Preferably, the welding method is: start welding with a smaller welding current, weld three welds at each current, observe the spattering of the welds, continue welding with a current increase of 0.1-0.2kA until spattering occurs at least at one of the welds, and then stop welding.

[0027] Further preferably, the current value for stopping welding is -0.1 or 0.2 kA, which is the selected welding current.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The welding method for improving the plating protrusion of the zinc-aluminum-magnesium coated steel plate weld point provided by the present invention solves the problem of plating protrusion of the zinc-aluminum-magnesium coated steel plate weld point and the welding problems that are easy to occur in conventional welds, such as cold welding, severe spatter and low weld strength.

[0030] The welding method for improving the coating bulge of the zinc-aluminum-magnesium coated steel plate weld point provided by the present invention is based on the composition optimization strategy of high magnesium, low aluminum and high silicon in the coating and the "two big, one small and one critical" welding process solution. Among them, "two big" refers to the large preheating current and long welding time; "one small" refers to the small coating weight; "one critical" refers to the critical welding current at which the critical weld point is in a spattering state but no spatter occurs.

[0031] The welding process parameter control of the present invention has an important influence on the zinc protrusion and strength of the weld. The present invention adopts a large preheating current and a thin coating thickness. Through the reasonable combination of welding time and welding current, the coating of the weld can be quickly heated up and the evaporation of the coating can be accelerated. The zinc ring area can be increased, the degree of zinc liquid accumulation can be weakened, the zinc liquid evaporation time can be extended, and the amount of zinc liquid accumulation can be reduced. The extra force generated during the weld splashing process further promotes the extreme segregation of zinc liquid, so that the weld reaches a critical splashing but non-splashing state, which can not only ensure that there is no false welding, but also that the welding strength of the weld meets the standard.

[0032] The present invention not only fills the blank of the method for improving the coating protrusion of the welding spot of the low-aluminum-zinc-aluminum-magnesium coated steel plate, but also solves the problems of poor welding performance of the existing low-aluminum-zinc-aluminum-magnesium coated plates and poor weld quality between the low-aluminum-zinc-aluminum-magnesium coated plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The macroscopic morphology of the weld surface corresponding to three different welding currents in Example 1: (a) 8.6kA, (b) 9.8kA,

[0034] (c) 10.0 kA;

[0035] Figure 2 The macroscopic morphology of the solder joint surface corresponding to three different coating weights and welding process parameters in Example 2;

[0036] Figure 3 The macroscopic morphology of the weld surface corresponding to the three low-aluminum-zinc-aluminum-magnesium coated steel plates with different chemical compositions in Example 3. DETAILED DESCRIPTION

[0037] The specific implementation of the technical solution of this specification is further described below in conjunction with the accompanying drawings through specific embodiments. These embodiments are for the purpose of describing the technical solution in detail, rather than for limiting the technical solution. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this specification.

[0038] Example 1

[0039] The present embodiment provides a two-layer plate group, which is welded together by two layers of zinc-aluminum-magnesium steel plates of the same thickness. The thickness of each layer of steel plate is 0.65 mm. The chemical composition of the low-aluminum zinc-aluminum-magnesium coating (grade DC54-ZM, denoted as ZM) includes 1.4% Al, 1.6% Mg, 0.62% Si, and the rest is Zn. The coating weight is 40-45 g / m 2 .

[0040] Before welding, use alcohol to clean the dirt on the surface of the steel plate until there is no foreign matter visible to the naked eye.

[0041] The welding process adopts two-stage welding, with a preheating current of 10kA and a welding time of 500ms. Welding starts with a welding current of 8.0kA, and three welds are welded at each current to observe the spatter of the welds; welding continues with a current increase of 0.2kA. When the welding current increases to 10.0kA, spatter occurs at one of the three welds, and the welding process ends.

[0042] Comparing the convexity of the solder joint coating under the three welding currents of 8.6, 9.8 and 10.0 kA, the macroscopic morphology of the solder joint surface is shown in Figure 1 .

[0043] Depend on Figure 1 It can be seen that the welding current corresponding to the weld with the lightest zinc convex problem is 9.8kA, that is, the weld reaches the critical spatter but no spatter state, and the weld zinc convex problem is significantly improved. In addition, at this welding current, the weld does not have welding spatter, and the weld strength can also meet the requirements.

[0044] Example 2

[0045] This embodiment provides a two-layer plate set, which is welded together by 0.8mm (HC220YD-GI) and 0.65mm (DC56-ZM). Specific material information and welding process parameters are shown in Table 1. The chemical composition of the low aluminum zinc aluminum magnesium coating (ZM) includes 1.3% Al content, 1.8% Mg content, 0.70% Si content, and the rest is Zn.

[0046] Before welding, use alcohol to clean the dirt on the surface of the steel plate until there is no foreign matter visible to the naked eye.

[0047] The welding process adopts two-stage welding. The key welding process parameters and predicted minimum spatter current are shown in Table 1.

[0048] Comparing the convexity of the solder joint coating of ①, ②, and ③, the macroscopic morphology of the solder joint surface is shown in Figure 2 .

[0049] It can be seen that the coating weight and key welding parameter values ​​of ③ are within the ideal range, and the zinc convexity of the weld is not obvious. In addition, under the welding current in the table, the weld does not produce welding spatter, and the weld strength can meet the requirements.

[0050] Table 1 Material information and welding process parameters

[0051]

[0052] Example 3

[0053] This embodiment provides a two-layer plate set, and the material information and welding process parameters are shown in Table 2. Table 3 Chemical composition of low aluminum zinc aluminum magnesium coating and zinc convex results of welding points.

[0054] It can be seen from Table 2 combined with Example 2 that the welding process parameters of ③, ④, ⑤ and ⑥ are all optimal values.

[0055] It can be seen that except for ③, the low aluminum-zinc-aluminum-magnesium coating composition in the plate groups ④, ⑤ and ⑥ does not meet the requirements of the present invention. The macroscopic morphology of the surface of the welding points ④, ⑤ and ⑥ is shown in Figure 3. Figure 3 , there is obvious zinc layer protrusion phenomenon in all welding points.

[0056] Table 2 Material information and welding process parameters

[0057]

[0058] Table 3 Composition (mass fraction) of low aluminum-zinc-aluminum-magnesium coating

[0059]

[0061] Although the embodiments of the present description have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present description, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A welding method for improving the coating protrusion of the welding point of zinc-aluminum-magnesium coated steel plate, characterized in that: The following steps are involved: (1) preparing zinc-aluminum-magnesium coated steel plates with a sheet thickness of ≤3 mm to be welded, overlapping them into two or three layers of plates for welding, wherein at least one outermost layer is a zinc-aluminum-magnesium coated steel plate; (2) Before welding, use alcohol to clean the surface of the steel plate until there is no foreign matter visible to the naked eye; Welding adopts two-stage welding, including preheating stage and welding stage. The preheating stage includes preheating time and preheating current. (3) and cooling time. The welding section includes welding time, welding current and cooling time.

2. The welding method for improving the coating protrusion of the zinc-aluminum-magnesium coated steel plate welding point according to claim 1 is characterized in that: The components of the zinc-aluminum-magnesium coating, in terms of mass percentage, include: Mg: 1.5% to 3.0%, Al: 1.0% to 1.5%, Si: 0.6% to 0.8%, and the rest is Zn.

3. The welding method for improving the coating protrusion of the zinc-aluminum-magnesium coated steel plate welding point according to claim 1 is characterized in that: The single-piece thickness of the zinc-aluminum-magnesium coated steel plate to be welded is ≤1mm.

4. The welding method for improving the coating protrusion of the zinc-aluminum-magnesium coated steel plate welding point according to claim 1 is characterized in that: The weight of the zinc-aluminum-magnesium coating shall not exceed 50 g / m 2 .

5. The welding method for improving the coating protrusion of the welding point of zinc-aluminum-magnesium coated steel plate according to claim 4 is characterized in that: The weight of the zinc-aluminum-magnesium coating is 42-50 g / m 2 .

6. The welding method for improving the coating protrusion of the welding point of zinc-aluminum-magnesium coated steel plate according to claim 5 is characterized in that: The weight of the zinc-aluminum-magnesium coating is 42-45 g / m 2 .

7. The welding method for improving the coating protrusion of the welding spot of the zinc-aluminum-magnesium coated steel plate according to claim 1 is characterized in that: The preheating current is 10-14 kA.

8. The welding method for improving the coating protrusion of the welding spot of the zinc-aluminum-magnesium coated steel plate according to claim 1 is characterized in that: The welding time is not shorter than 500ms.

9. The welding method for improving the coating protrusion of the welding spot of the zinc-aluminum-magnesium coated steel plate according to claim 1 is characterized in that: The welding method is as follows: start welding with a relatively small welding current, weld three welds at each current, observe the spattering of the welds, continue welding with a current increase of 0.1-0.2 kA, until spattering occurs at least at one of the welds, and then stop welding.

10. The welding method for improving the coating protrusion of the welding point of zinc-aluminum-magnesium coated steel plate according to claim 9, characterized in that: The current value for stopping welding is -0.1 or 0.2 kA.

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