JPH0688287A - Zn-fe-alloy-plated al alloy plate excellent in resistance weldability - Google Patents

Abstract

PURPOSE:To produce a Zn-Fe-alloy-plated Al alloy plate excellent in resistance weldability by forming a Zn-Fe-alloy-plated layer specified in Fe content and plating weight on the one or both side of Al or Al alloy plate. CONSTITUTION:The surface of aluminum (alloy) plate is applied with a substituted Zn plated layer having about 0.5g/m<2> METSUKE(unit) weight by using a zincate bath. Next, the Zn-Fe-alloy-plated layer having 5-60wt.% Fe content and 6-60g/m<2> plating weight is formed on one or both side of the aluminum plate by cathode-electrolyzing in an aq. solution containing zinc sulfate and iron sulfate by using the aluminum plate as a cathode. Thus, the aluminum plate having excellent resistance weldability is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Zn-based alloy-plated Al alloy plate, and more particularly to a Zn-Fe alloy-plated plate which has excellent resistance weldability and can be applied to various applications such as an Al alloy plate for automobiles. It relates to an Al plate.

[0002]

2. Description of the Related Art Conventionally, automobile manufacturers have used steel sheets for automobile bodies. The steel plate referred to here is a plain steel plate, a high-strength steel plate, a Zn-based electroplated steel plate, or a Zn-based hot dip plated steel plate. Of these, surface-treated steel sheets such as Zn-plated steel sheets are excellent in corrosion resistance, and are therefore widely used in areas where corrosion is likely to occur, such as fenders and door panels. On the other hand, recently, there has been a demand for using an aluminum plate for a body of an automobile, mainly for the purpose of reducing the vehicle body weight for improving the fuel efficiency and power performance of the automobile. However, it is rare at present to manufacture an entire body of an automobile from an aluminum plate, and in general, a part of the body is replaced with a steel plate from an aluminum plate. Therefore, an automobile body is assembled by using a steel plate and an aluminum plate together.

In an automobile body assembly / manufacturing line, a body steel plate and an aluminum plate are formed into a predetermined shape by pressing or the like, and then these members are spot-welded by resistance welding to be assembled into a body.
Most of the body assembly process by resistance welding is currently performed by an automatic assembly robot, and it is desired to assemble the above-mentioned member made of a steel plate and an aluminum plate under welding conditions of a member made of only a steel plate. . By doing so, even when a steel plate and an aluminum plate are used together, it is not necessary to change the welding conditions each time depending on the welding site, and the continuity of the process is maintained, which is advantageous in terms of manufacturing cost. Several attempts have been made with regard to zinc phosphate treatability as a pretreatment for painting, in order to bring the properties of an aluminum plate required for assembling an automobile body closer to those of a steel plate.

For example, JP-A-61-157693, JP-A-4-17677, and JP-A-4-1767.
No. 8, Japanese Patent Application Laid-Open No. 4-17679, Japanese Patent Application Laid-Open No. 4-1
Japanese Patent No. 7680 proposes a method of applying a Zn plating layer to an aluminum plate as a method of improving the zinc phosphate treatment property of the aluminum plate. On the other hand, there is little related to resistance weldability, and there is a method of improving continuous spotting property at the time of resistance welding by a plating treatment method comprising two layers of a Ni plating layer and a Zn-based alloy plating layer, which is found in JP-A-3-146693. Proposed. However, a surface treatment method that is simpler and has excellent resistance weldability is desired from the viewpoint of the complexity of the process by the two-layer plating treatment and the manufacturing cost. Therefore, as in the present invention, none of the Zn-Fe alloy plated layers, which define the composition of the plated layer and the amount of the deposited coating, remarkably improve the resistance weldability of the Al alloy plate.

[0005]

Regarding the resistance weldability of an aluminum plate in a vehicle body assembly process in which a steel plate and an aluminum plate are used in combination, those having a welding current value equal to or close to that of a cold rolled steel plate are considered to be good. However, the aluminum plate has a drawback that the welding current value becomes too large as compared with the steel plate. The reason for this is currently unknown. Probably, it is speculated that aluminum has a lower melting point than steel and has a good thermal conductivity, so it easily melts, so the electrical conductivity becomes too high and the area of the fused part becomes too large at the same time. . Accordingly, the present invention provides an aluminum plate that solves the above problems, that is, an aluminum plate having a welding current value equal to or close to that of a steel plate and excellent in resistance weldability.

[0006]

DISCLOSURE OF THE INVENTION As a result of various investigations made by the present inventors in view of the above-mentioned circumstances, in a Zn--Fe alloy plated aluminum plate, if the composition of the plating layer and the basis weight are specified, excellent resistance weldability is obtained. The present invention was made by finding that an aluminum plate having The gist of the present invention is to provide one or both sides of an Al or Al alloy plate with F
e content is 5 to 60% by weight, and coating weight is 6 to 6
Zn-Fe alloy plated Al having excellent resistance weldability, characterized by having a Zn-Fe alloy plated layer of 0 g / m ^2.
It is an alloy plate.

[0007]

Next, the present invention will be described in detail. The Zn-Fe alloy plating layer is formed by coating the aluminum surface,
Suppresses the formation of an insulative passive film of aluminum.
Further, the welding current value is set to an appropriate value by suppressing an excessive increase in electric conductivity due to melting of aluminum during resistance welding. Although the reason for its action is unknown, it is believed that the melting point, electrical conductivity, and thermal conductivity of the Zn-Fe alloy plating layer influence. That is, the Zn-Fe alloy is F
When the e content is in the range of 5 to 60% by weight, the phases of ζ, δ and Γ are in order from the Fe content is the lowest, but all have a higher melting point than pure zinc and have a melting point of Al or higher. Indicates a value. In addition, since the electrical conductivity and thermal conductivity are smaller than that of aluminum, the optimum welding current value during resistance welding becomes small due to the physical properties of these Zn-Fe alloy layers, and the current is close to that of cold-rolled steel sheets. It is thought that it became a value.

Therefore, it is important to control the physical properties of the Zn--Fe alloy layer to optimum values, but as a result of various studies by the present inventors, the Fe content in the Zn--Fe alloy layer was 5%. To 60% by weight, it was found to be good. Fe content less than 5% by weight or 60% by weight
If the value is larger, the welding current value is significantly different from the value of the cold-rolled steel sheet, which is not suitable. The coating weight is 6 g /
When the value is smaller than m ^{2, the} thickness is too thin as compared with the thickness of an aluminum plate that is usually used as a vehicle body outer plate, and there is no effect. On the other hand, although there is no particular upper limit, it is 60 g / m ² or less considering pressability and economy.

The material of the present invention is excellent in zinc phosphate treatment, which is widely used as a coating base treatment, but it is possible to obtain a coating equivalent to the chemical conversion coating formed on a cold rolled steel sheet, or to lubricate the sheet. Fe-Zn containing 5 to 20% by weight of Fe plating layer or Zn for the purpose of improving the property
Even if the alloy plating layer is applied in an amount of about 1 to 5 g / m ^2, it does not hinder the action of the Zn—Fe alloy layer of the material of the present invention as the lower layer, and there is no problem.

The present invention may be produced by a known plating method, and can be produced, for example, by a method in which various vapor deposition methods are combined, but it is usually produced by an electrolytic method. However, since aluminum generally has a markedly poor adhesion to plating, it is common to perform a base plating treatment. As a known undercoating treatment, a zincate method, an anodizing method, and a hot dipping method are known. Here, the zincate method is a displacement plating method using an alkali zinc bath, the anodizing method is a method of forming an anodic oxide film of aluminum and then plating, and the hot dipping method is electrolytic plating treatment followed by heat treatment. A method of forming an alloy diffusion layer on the plating interface. The former two methods both form a very small amount of underlayer on the plating interface and do not affect the action of the Zn—Fe alloy plating layer of the present invention. Also,
Even in the hot dipping method, there is no structural change that affects the operation of the present invention. As the electrolysis method, for example, after zincate treatment, cathodic electrolysis is performed at a current density of 5 to 200 A / dm ² using Pb as an anode and an aluminum plate as a cathode in an aqueous solution containing zinc sulfate and iron sulfate to form a Zn- Fe alloy plating is obtained. Hereinafter, the effects of the present invention will be described more specifically with reference to Examples.

[0011]

Example A substituted Zn plating layer having a basis weight of about 0.5 g / m ² was applied to the surface of an aluminum plate using a zincate bath, and then the aluminum plate was placed in an aqueous solution containing zinc sulfate and iron sulfate. Various Zn-Fe alloy plated Al alloy plates were produced by performing cathodic electrolysis under various conditions as a cathode. The resistance solution properties of the obtained Zn—Fe alloy plated aluminum plate were examined together with various comparative materials. The resistance weldability was evaluated by the spot welding method. The welding current value is measured under the following conditions: plate thickness 1.0 mm, electrode tip 4.5
mmφ, pressure 200 kg, welding time 10 cycles (5
0 Hz), an appropriate welding current value was obtained from the nugget diameter and the scattering occurrence condition, and the quality was judged by whether or not the value was close to that of the cold rolled steel sheet.

The results are shown in Table 1. No. in the table 1, 2,
3, 4, 5 are comparative materials, and others are the aluminum materials of the present invention. Fe content in the plating layer is less than 5 wt% or more than 60 wt%, and Fe content is 5 to 6
Even if it is in the range of 0% by weight, the coating weight is 6 g / m
Any aluminum plate having a Zn-Fe alloy plating layer smaller than ² has insufficient resistance weldability in terms of the proper welding current range during spot welding. In contrast,
All the materials of the present invention have good resistance weldability.

[0013]

[Table 1]

[0014]

INDUSTRIAL APPLICABILITY As described in detail above, the present invention is an aluminum plate provided with excellent resistance weldability, and its industrial value is extremely great.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Honda 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (1)

[Claims] 1. A Zn—Fe alloy plating layer having an Fe content of 5 to 60% by weight and a coating weight of 6 to 60 g / m ^{2 on} one or both sides of an Al or Al alloy plate. Zn-Fe alloy plated Al alloy plate with excellent resistance weldability.