JPH04365881A - Aluminum material having excellent spot resistance weldability - Google Patents

Abstract

PURPOSE:To prolong the service life of an electrode at the time of spot resistance welding of an Al material and to stabilize the quality of the resulting weld zone. CONSTITUTION:The surface of an Al or Al alloy sheet, is anodically oxidized to form an oxide film of 5-5,000Angstrom thickness and the surface of this film is coated with a metal for preventing the melt sticking of an electrode tip to the Al material in 0.01-10g/m<2> thickness. The metal is based on Zn, Cu, Sn, Cr, Ag, Ni or Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum material made of aluminum or an aluminum alloy, and relates to an aluminum material that has excellent spot resistance weldability and is mainly used as a lightweight material for automobiles. This is a proposal. [0002] In recent years, from the viewpoint of global environmental issues, particularly measures to prevent global warming caused by CO2, measures have been taken to reduce the weight of automobile bodies and improve fuel efficiency. Under these circumstances, aluminum and its alloys (hereinafter collectively referred to as metals) are considered to be metals that are well suited to this policy, as well as in terms of material reliability, workability, and recyclability. Aluminum materials (also called "aluminum materials") have been in the spotlight, and recently, their use as interior and exterior panels for automobile bodies is expanding. However, in order to assemble an automobile body using this aluminum material, welding, particularly spot resistance welding, is essential. However, the reality is that aluminum plates have extremely poor spot resistance weldability, particularly electrode life, compared to steel plates, resulting in a significant drop in production efficiency of vehicle bodies. In other words, in spot resistance welding of aluminum materials, welding phenomenon easily occurs and the number of welding points that can yield a proper nugget is extremely small, so electrode dressing or Replacement is required. This has a great negative effect on welding efficiency and, ultimately, on the production efficiency of automobile bodies. However, since this aluminum material has only recently been put into practical use as a material for automobile bodies, particularly as a material for spot resistance welding of automobile bodies, many of the above-mentioned problems remain unsolved. . Among the conventional techniques that have already been proposed, for example, Japanese Patent Application Laid-Open No. 60-1
There is a method, as disclosed in Japanese Patent No. 87483, in which the thickness of the oxide film on the bonding surface of aluminum plates is controlled by anodizing. In addition, although it is not intended for application to aluminum alloy plates for automobiles,
JP-A-6252, JP-A-53-48954, or JP-A-53-48955 discloses a method of interposing a Zn, Ti, or stainless steel thin film on the aluminum bonding surface, and JP-A-57-4389 The publication discloses a method of plating with Cr, Ni, Cu, or Ag. [Problems to be Solved by the Invention] However, the method disclosed in the above-mentioned Japanese Patent Application Laid-open No. 187483/1983 for controlling the anodic oxidation film is difficult to achieve uniform treatment and its effect is unstable, making it impractical. isn't it. Also, the above-mentioned Japanese Patent Application Laid-Open No. 53-625
The so-called Zn, Ti,
The improvement method by interposing a stainless steel thin film is as follows.
It is difficult to apply it to automobiles, and
The so-called Cr, Ni,
The improvement method of applying Cu or Ag plating also had the problem of poor adhesion of the plating to the aluminum material, making it impractical. The purpose of the present invention is to overcome the above-mentioned problems faced by each of the above-mentioned conventional techniques, and in particular, the electrode life during spot resistance welding, that is, the continuous dot performance, is significantly improved compared to conventional aluminum materials. It is an object of the present invention to provide a method that has excellent properties and can easily and stably perform spot welding of aluminum materials for automobile bodies industrially. [Means for Solving the Problems] In the course of intensive research aimed at achieving the above object, the present inventors conducted an experiment in which aluminum materials were continuously spot resistance welded using a copper-based electrode. However, it was found that the current-carrying diameter at the tip of the electrode gradually expanded in proportion to the number of dots, which caused a decrease in the current density in the plate and a decrease in the nugget diameter. That is, in the case of an aluminum material, the diameter of the electrode tip increases significantly faster than that of a steel plate, which causes a shortened electrode life. [0008] Further investigation into the cause revealed the following facts. That is, when aluminum materials are continuously spot welded, molten aluminum tends to adhere to the tip of the electrode, and the adhered aluminum is easily oxidized. Moreover, the oxide is deposited in proportion to the number of dots. As a result, this oxide deposited layer forms an insulating layer, which eventually leads to poor conduction between the electrode and this insulating layer, causing sparks. As a result, the electrode is damaged in a moth-eaten manner. On the other hand, the presence of an insulating oxide film on the surface of the aluminum material at the joint surface inhibits rapid welding. Such a phenomenon peculiar to the spot welding of aluminum materials promotes an enlargement of the electrode tip diameter and extremely shortens the life of the electrode. Based on such findings, the present invention was developed as a result of research into a method that prevents aluminum from adhering to the tip of the electrode during spot welding of aluminum materials and enables rapid welding at the joint surface. This is an effective welding method in which an oxide film is formed by anodizing one or both sides of a metal or alloy plate, and then the pores in the oxide film are used to prevent the electrode tip from adhering to the aluminum material during spot welding. We decided to apply a protective metal coating (plating treatment). By forming such a multilayer film of the base (anodized film) and the upper layer (metal film), plating adhesion is improved and at the same time, formation of aluminum oxide at the tip of the electrode is prevented. Furthermore, by imparting appropriate electrical resistance to the surface of the aluminum material at the joint interface, the aluminum materials can be easily welded together, thereby significantly improving the life of the electrode. [0010] The thickness of the oxide film is 5 to 500 mm.
At 0 Å, the coating weight of the welding prevention metal is 0.01 to 10
g/m2 is preferable, and the welding prevention metal coating is preferably a Zn-based plating containing Zn as a main component, C
Cu-based plating containing u as the main component, Sn-based plating containing Sn as the main component, Cr-based plating containing Cr as the main component,
Any one of Ag-based plating containing Ag as the main component, Ni-based plating containing Ni as the main component, or Fe-based plating containing Fe as the main component is used. [Operation] The anodic oxide film formed on the base of the aluminum material of the present invention is obtained by activating the aluminum alloy surface in advance using caustic soda or nitric acid solution, and then activating it in an acid solution such as phosphoric acid or sulfuric acid. A uniform oxide film formed by anodizing with constant current or constant potential. Here, the anodic oxidation treatment for forming the oxide film is preferably a constant current treatment using a phosphoric acid solution because the pores in the oxide film to be formed are large and the film thickness can be easily controlled. The thickness of the oxide film is 5 to 5
000 Å is preferred. The reason for this is that if the thickness is less than 5 Å, the adhesion of the upper layer zinc plating will be poor;
If it exceeds Å, it becomes difficult to perform upper layer plating, and the anodizing treatment time becomes longer, making it uneconomical. A more preferable thickness of the oxide film is 50 to 500 Å. In order for the aluminum material according to the present invention to exhibit excellent spot resistance weldability, the surface of the oxide film is further plated with a metal suitable for preventing welding between the electrode tip and the aluminum material during spot welding. It is necessary to. In this plating coating, it is extremely effective to impregnate the molten plating metal into the pores of the film to provide an anchor effect in increasing the adhesion of the plating film. In this sense, it is desirable that the welding prevention metal be coated through the pores. Now, as the welding prevention metal formed on the surface of the aluminum material to prevent welding between the electrode tip and the aluminum material mentioned above, one of the metals listed below is used. [0014] Zn-based plating containing Zn as the main component: This is Zn single phase or Zn-Fe, Zn-Cu, Zn-Ni, Zn-Mn, Zn containing 70 wt% or more of Zn.
n-Ag, Zn-Cr, Zn-Sn, Zn-P, Zn-
Refers to alloy plating such as B, Zn-C, etc. These are preferably laminated in two or more layers. ■Cu-based plating with Cu as the main component: This is
u single phase or Cu-Zn containing 70 wt% or more of Cu,
Cu-Fe, Cu-Ni, Cu-Mn, Cu-Ag, C
u-Cr, Cu-Sn, Cu-P, Cu-B, Cu-C
Refers to alloy plating such as. These are preferably laminated in two or more layers. ■Sn-based plating whose main component is Sn: This is S
n single phase or Sn-Zn containing 70 wt% or more of Sn,
Sn-Fe, Sn-Ni, Sn-Mn, Sn-Cu,
Sn-Ag, Sn-Cr, Sn-P, Sn-B, Sn-
Refers to alloy plating such as C. These are preferably laminated in two or more layers. ■Cr-based plating whose main component is Cr: This is
r Single phase or Cr-Zn containing 70 wt% or more of Cr,
Cr-Fe, Cr-Ni, Cr-Mn, Cr-Cu, C
r-Ag, Cr-Sn, Cr-P, Cr-B, Cr-C
Refers to alloy plating such as. These are preferably laminated in two or more layers. ■Ag-based plating with Ag as the main component: This is A
g Single phase or Ag-Zn containing 70 wt% or more of Ag,
Ag-Fe, Ag-Ni, Ag-Mn, Ag-Cu, A
g-Cr, Ag-Sn, Ag-P, Ag-B, Ag-C
Refers to alloy plating such as. These are preferably laminated in two or more layers. ■Ni-based plating with Ni as the main component: This is
i Single phase or Ni-Zn containing 70 wt% or more of Ni,
Ni-Fe, Ni-Mn, Ni-Ag, Ni-Cr, N
Refers to alloy plating such as i-Sn, Ni-P, Ni-B, and Ni-C. These are preferably laminated in two or more layers. ■Fe-based plating with Fe as the main component: This is F
e Single phase or Fe-Zn containing 70 wt% or more of Fe,
Fe-Ni, Fe-Mn, Fe-Ag, Fe-Cr, F
e-Cu, Fe-Sn, Fe-P, Fe-B, Fe-C
Refers to alloy plating such as. These are preferably laminated in two or more layers. [0015] When plating each of the metals or alloys listed above, the basis weight of the plating layer is 0.01 to 10 g/m.
About 2 is preferable. The reason is that if it is less than 0.01 g/m2, there is no effect, while if it exceeds 10 g/m2, the effect is saturated and it is uneconomical. For example, in the case of Fe-based plating, the preferred coating amount is 1 to 5 g/m2. Note that this plating may be applied only to one side of the aluminum material facing the electrode, but it goes without saying that the effect will be greater if both sides are plated. [Example] A 1 mm thick A5020 alloy (Al-2.5% Mg-0.25% Cr), which is a typical aluminum alloy plate used as a material for automobile bodies, was first used. After vapor degreasing the surface with trichlorethylene, surface activation treatment was performed using caustic soda and nitric acid solution. Next, both sides of this aluminum alloy plate were anodized under the following conditions. (Anodizing treatment conditions) Phosphoric acid: 350g/liter bath temperature
: 25° C. Current density: 1 A/dm2 The oxide film thickness was adjusted by changing the treatment time. The surface of the oxide film of the aluminum alloy thus anodized is coated with an aqueous electroplating method.
The following plating was applied. (A) Zn-based plating
(E) Ag-based plating (A-1
) Pure Zn plating
(E-1) Pure Ag plating (A-2) Zn-
Fe plating (E
-2) Ag-Zn plating (A-3) Zn-Ni
Plating (E-3
) Ag-Ni plating (B) Cu-based plating
(F) Ni-based plating (B-1) Pure Cu plating
(F-1) Pure Ni plating
(B-2) Cu-Zn plating
(F-2) Ni-Zn plating (
B-3) Cu-Ni plating
(F-3) Ni-Cu plating (C) Sn-based plating
(G) Fe-based plating (C-1) Pure Sn plating (G-1)
Pure Fe plating (C-2) Sn-Fe plating
(G-2) Fe-Z
n plating (C-3) Sn-Ni plating
(G-3) Fe-P plating (D) Cr-based plating (D-1) Pure Cr plating (D-2) Cr-Fe plating (D-3) Cr-Ni plating 0020
The electrode life of the aluminum alloy plate after plating was evaluated using the following electrode and welding conditions using an inverter DC welding machine. The evaluation was based on the number of dots until welding or the number of dots until the nugget diameter fell below 4 roots t (t: plate thickness), whichever was smaller. The evaluation criteria were that a score of less than 1,000 points was considered poor (×), and a score of 1,000 or more was considered good (○). [0021] (Electrode) ・Shape: Cone-shaped (CF) type ・Tip diameter: 5.0mmφ ・Material
: Cr-Cu (welding conditions) - Pressure: 150 kgf - Initial pressurization time: 20/50 seconds - Current application time: 6/50 seconds - Holding time: 5/50 seconds - Welding current: 15 kA Example of the present invention and Comparative Examples are summarized in Tables 1 to 7. As is clear from Tables 1 to 7, it can be seen that the present invention is extremely effective in improving the spot weldability of aluminum alloy plates. [Table 1] [Table 2] [Table 2] [Table 3] [0025] [Table 4] [Table 5] [Table 5] [Table 6] [Table 7] Effects of the Invention As explained above, the aluminum material of the present invention is made by applying an anodic oxide film and plating with a welding prevention metal/alloy such as Zn or Fe to the surface of aluminum or aluminum alloy. , the electrode life during spot resistance welding is significantly improved. This significantly reduces the frequency of changing electrodes or shaping the tip shape by dressing during spot welding at production sites, leading to a significant increase in productivity, and at the same time dramatically improving the stability of the quality of welded parts. You can also expect good results.

Claims (3)

[Claims] 1. An aluminum material having excellent spot resistance weldability, which is obtained by providing an anodized film on one or both sides of an aluminum material made of aluminum or an aluminum alloy, and coating the surface of this oxide film with a welding prevention metal. 2. The thickness of the oxide film is 5 to 5000 Å.
and the adhesion amount of the welding prevention metal is 0.01 to 10 g/m
2. The aluminum material according to claim 1. 3. The welding prevention metal coating is a Zn-based plating containing Zn as a main component, or a Cu coating containing Cu as a main component.
plating, Sn-based plating with Sn as the main component, Cr-based plating with Cr as the main component, A-based plating with Ag as the main component
The aluminum material according to claim 1 or 2, which is any one of g-based plating, Ni-based plating containing Ni as a main component, or Fe-based plating containing Fe as a main component.