JPS62112773A - Surface treated steel sheet for automobile - Google Patents

Abstract

PURPOSE:To improve the workability of a steel sheet and the pitting resistance of the inside of an automobile body of the steel sheet by forming an Al layer of a desired thickness on the side of the steel sheet and a plated Zn-base layer on the other side. CONSTITUTION:An Al layer of >=2mum thickness is formed on one side of a steel sheet for an automobile by vacuum deposition. A plated Zn or Zn alloy layer is formed on the other side of the steel sheet to such a degree that the cold workability is not deteriorated. The resulting surface treated steel sheet has superior workability and the inside of an automobile body made of the steel sheet has superior pitting resistance.

Description

[Detailed description of the invention] [Industrial field] The present invention relates to a surface-treated steel sheet for automobiles.

[Prior Art] Conventionally, as a surface-treated steel sheet for an automobile body, a steel sheet coated with galvanization on one side or a zinc-based alloy such as zinc-nickel or zinc-iron has been used. These treated steel plates are intended to prevent rust on the inner surface of the body, where the adhesive coating will not go around.

Approximately, corrosion resistance requirements for automobile bodies are becoming stricter.1 For example, the Canadian Code requires a 5-year guarantee against corrosion due to holes, and the target value is becoming 10 years.

As described above, surface-treated steel sheets for automobiles are required to have high corrosion resistance.

[Problems to be Solved by the Invention] In order to satisfy such requirements for corrosion resistance, it is conceivable to increase the thickness of the above-mentioned zinc or zinc alloy plating film, but if the plating film thickness is increased, There was a problem that peeling and cracking of the plating layer occurred during cold working, making press forming impossible.

This is because the workability of the zinc-based plating layer is poor.

Instead of zinc-based plating, aluminum plating can be considered as a plating layer having a sacrificial anticorrosion effect.

However, aluminum plating has the problem that it cannot be manufactured using normal electroplating methods.On the other hand, in hot-dip plating methods, the high temperature of the plating bath creates an aluminum-iron alloy layer at the interface with the steel sheet, which deteriorates the sacrificial corrosion protection effect. Moreover, the workability of the aluminum-iron alloy layer is extremely poor, and the plating layer peels and cracks occur during cold working, resulting in a number of problems such as loss of corrosion resistance. For this reason, this aluminum plating has not been considered at all as a surface-treated steel sheet for automobile bodies.

[Means for Solving the Problem] The surface-treated steel sheet for automobiles of the present invention is characterized in that two or more aluminum layers are vacuum-deposited on one side of the steel sheet.

A zinc or other zinc-based plating layer may be formed on the other surface of the steel sheet, that is, the surface that will become the outer surface of the automobile body, to the extent that cold workability is not impaired.

[Function] When applying aluminum plating to a steel plate using the vacuum evaporation method, it is necessary to heat the underlying steel plate to a temperature of 150°C or higher in order to improve the adhesion of the plating. Heating the steel plate by radiant heat from
By adjusting the temperature to below 00°C, it is possible to prevent the formation of an aluminum-iron alloy at the interface between the steel sheet and the plating layer. As a result, it is possible to solve the problem of deterioration in workability due to the formation of an aluminum-iron alloy. The vacuum-deposited aluminum plating layer has very few impurities, so it has excellent ductility and has very little adverse effect on processing (cold working) during automobile body molding.

Furthermore, since an aluminum-iron alloy layer is not formed at the interface between the aluminum plating layer and the steel sheet, the sacrificial anticorrosion effect of aluminum can also be maintained. Regarding this sacrificial corrosion protection, the elution rate of aluminum is slower than that of the zinc-based plating layer, so it is possible to improve the large crack resistance of the automobile body, and it is also possible to make the plating layer thinner. It was found that an aluminum plating layer of two or more wells could be used to match the large crack resistance when the zinc plating film thickness was 5 tiles.

[Example] The present invention will be explained in detail below.

As shown in Table 1, surface-treated steel sheets for automobiles are made by forming a plating layer 2 on one side of a steel sheet 1.
Created various types from A to NoI.

The large crack resistance was investigated in the automobile cycle test shown in Table 2.

Table 1 Table 2 Table 3 shows the results of the above test, NoE, F.

It can be seen that the material of Example G according to the present invention has superior large crack resistance compared to the comparative material having a zinc-based plating layer formed thereon.

Table 3 In addition, in order to evaluate the workability of the plating layer, a close bending test was conducted with the plating layer on the outside, and the processed surface was examined using a microscope. The results are as shown in Table 4, NoE, F. ,
It was also found that the workability of Example G of the present invention was good.

Table 4 [Effects of the Invention] As explained above, according to the present invention, the effect of providing a surface-treated steel sheet for automobiles that can improve the resistance to large cracks on the inner surface of an automobile body and also has excellent workability. There is.

[Brief explanation of drawings]

The drawing is a partially enlarged view of the embodiment. l... Steel plate, 2... Plating layer.

Claims (1)

[Scope of Claims] 1. A surface-treated steel sheet for automobiles, characterized in that an aluminum layer of 2μ or more is vacuum-deposited on one side of the steel sheet. 2. The surface-treated steel sheet for automobiles according to claim 1, wherein a zinc or other zinc-based plating layer is formed on the other side of the steel sheet.