JPH04323384A - Aluminum sheet or aluminum alloy sheet excellent in spot weldability and its production - Google Patents

Abstract

PURPOSE:To improve the spot weldability and chemical convertibility of an aluminum sheet or an aluminum alloy sheet by subjecting a plated film for chemical conversion treatment formed on the surface of an aluminum series metallic sheet to heating treatment and thereafter furthermore forming an oxidized film. CONSTITUTION:For example, electroplating or the like is applied to the surface of an aluminum sheet or an aluminum alloy sheet to form a plated film for chemical conversion treatment. Next, the aluminum (alloy) sheet after the above plating is heated, e.g. to 200 to 500 deg.C, and after that, an oxidized film is formed. This oxidized film is formed by bringing the sheet into contact with a mixture of air and steam or steam, bringing it into contact with a soln. of zinc nitrate or subjecting it to electrolysis treatment in an aq. soln.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum plate or aluminum alloy plate with excellent spot weldability and a method for manufacturing the same.

0002

BACKGROUND OF THE INVENTION Recently, aluminum plates or aluminum alloy plates (hereinafter referred to as Al plates) have been increasingly applied to automobile materials and building materials. In such applications of Al plates, joining by spot welding and painting are essential, but compared to galvanized steel plates or cold-rolled steel plates, weldability is inferior,
Furthermore, if a chemical conversion treatment solution is used for galvanized steel sheets or cold-rolled steel sheets in a painting treatment line, a part of the Al plate (Al) will be eluted into the treatment solution, causing disadvantages such as adverse effects.

0003

SUMMARY OF THE INVENTION In view of the current situation, it is an object of the present invention to provide an aluminum plate or aluminum alloy plate with excellent spot weldability and a method for manufacturing the same.

0004

[Means for Solving the Problems] The gist of the present invention is as follows. (1) An aluminum plate or aluminum alloy plate with excellent spot weldability, characterized in that a plating film for chemical conversion treatment is formed on the surface of the aluminum plate or aluminum alloy plate, and an oxide film is formed on the film layer.

(2) Generating a plating film for chemical conversion treatment on the surface of an aluminum plate or an aluminum alloy plate,
A method for producing an aluminum plate or aluminum alloy plate with excellent spot weldability, which comprises heating the plate and then contacting it with a steam/water mixture or steam to form an oxide film. (3) A spot characterized by forming a plating film for chemical conversion treatment on the surface of an aluminum plate or aluminum alloy plate, and then forming an oxide film by contacting it with an aqueous zinc nitrate solution or electrolytically treating it in the aqueous solution. A method for manufacturing aluminum plates or aluminum alloy plates with excellent weldability.

That is, the present invention provides a plating film for chemical conversion treatment on Al plate ( The main idea is to generate it on the surface of the plate (with a thickness of 0.4 to 9.0 mm). As such a plating film, for example, a zinc-based film, particularly zinc, or zinc-iron (iron content of 95% or less), which fully exhibits the above-mentioned functions, is preferable.
By setting the plating amount to 0.1 to 10 g/m2, chemical conversion treatment properties can be improved and oxide generation can be ensured.

[0007] Before performing the treatment of the present invention, it is preferable to wash and remove the oxide film existing on the surface of the Al plate. For example, N
The Al2O3-based oxide film can be removed by immersion in an aOH (1-5%) aqueous solution or by electrolytic treatment. In order to clean the Al plate, it is preferable to immerse it in an aqueous solution of a weakly alkaline cleaning agent such as sodium phosphate, or to perform electrolytic treatment. Pickling can be added if necessary. Thereafter, it is washed with water and subjected to a plating film treatment to improve chemical conversion treatment properties.

[0008] Further, as a plating method, electroplating,
Flash plating, vapor deposition plating, electroless plating, thermal spraying, etc. are suitable. In addition to pure Zn, the plating composition includes Zn
and Fe, Zn and Ni, Zn and Al, Zn and Mn, etc.
The main component is one or more alloying elements and impurity elements to improve various functions such as corrosion resistance, and the plating layer is made of ceramic fine particles such as SiO2, Al2O3, oxides such as TiO2, and organic polymers. There is something dispersed inside. There are those with a single composition in the thickness direction of the plating layer, and those with a composition that changes continuously or layered.Furthermore, in multi-layer plated steel sheets, the top layer is mainly composed of Fe and Ni, but also contains various alloying elements such as Zn and P. There is something.

[0009] Thus, such a plating film is fully compatible with a chemical conversion treatment solution that is highly suitable for galvanized steel sheets currently used in automobiles and various home appliances in which galvanized steel sheets are widely used. If an Al plate without such a plating film is simultaneously treated with a chemical conversion treatment solution for galvanized steel sheets, the quality of the chemical conversion film will deteriorate, especially the occurrence of scratches, and the quality of the subsequent coating, that is, the coating. This not only significantly reduces corrosion resistance, but also causes Al to be eluted into the treatment solution, resulting in significant deterioration of the treatment solution, making it necessary to frequently replace the solution in order to maintain the quality of the chemical conversion coating on galvanized steel sheets. Alternatively, in order to solve this problem, it is necessary to introduce a chemical conversion treatment equipment exclusively for Al plates, so the treatment cost increases in either case.

[0010] Next, as a method for generating oxides on the plated surface to improve spot weldability, when the oxides are generated by contacting with a steam/water mixture or water vapor, the plated Al plate has a After heating to 500°C, the ZnO-based oxide 2 is brought into contact by spraying with a mixture of air and water as described above.
It is possible to reliably generate 0 to 3000 mg/m2.

[0011] In addition, when generating an oxide by contacting with an aqueous solution of zinc nitrate, 200 to 800 g of zinc nitrate is added.
ZnO
The main oxide can be reliably generated. Furthermore, in the case of electrolysis, the amount of electricity is 5 to 80 C/dm2 in the zinc nitrate aqueous solution as described above, and the time is 0.1 to 10
By performing the electrolytic treatment using the Al plate as a cathode, it is possible to reliably generate an oxide mainly composed of ZnO.

[0012] The oxide to be formed on the surface of the plating film for chemical conversion treatment is an oxide containing, in addition to ZnO, components such as component elements contained in the plating layer or compounds such as their oxides. But that's fine. Further, in electrochemical treatment such as anodic oxidation, a component or a compound contained in a treatment liquid may be included. The amount of such oxide produced is the amount of ZnO in the oxide (per one side).
As a result, 20 to 3000 mg/m2 is required. Z
There is no effect when the amount of nO is less than 20 mg/m2, and
If it exceeds 000 mg/m2, chemical conversion treatment becomes difficult, which is not preferable.

Such oxides can be obtained by, for example, dissolving the plating layer with a 5% iodine methanol solution, melting the extraction residue with a mixed melt (boric acid: 1 part, sodium carbonate: 3 parts), and then dissolving it in hydrochloric acid and analyzing it by ICP. Either the amount of zinc is converted to ZnO, or the oxygen integrated intensity value for 1 second from the outermost surface measured by glow discharge spectroscopy (GDS) is 1.0 to 10 VS (
By setting the value to 1 (per side), it is possible to accurately grasp the information.

That is, when attempting to join Al plates by spot welding, the Al layer becomes molten due to the heat generated during welding, and the copper of the electrode tip composition reacts selectively with the Al metal, causing the hard and brittle alloy layer to melt. Since the electrode tip is formed and easily destroyed by the pressure applied to the electrode, the electrode tip is worn out and the life of the electrode tip is shortened. However, when zinc oxide is present between the electrode tip and the Al plate (plating layer), this layer has the effect of preventing selective alloying of copper and aluminum, thereby delaying wear of the electrode tip. The reason for this is that the layer cuts off contact between the electrode tip and the Al plate (plated metal), prevents melting damage due to the formation of an alloy layer, and
Furthermore, oxides adhere to the tip of the electrode tip, accumulate and become a protective film for the electrode tip, and even if welding continues, the thickness and shape of the protective film do not change significantly, ensuring good welding at all times.
This is also considered to be because damage to the electrode tip can be prevented.

The Al plate to which the present invention is applied is Al-Cu type A
It includes Al alloy plates such as l-Mg type and Al-Mg-Si type, and can also be applied even if other components such as Fe, Mn, Cr, Zn, and Ti are included.

[0016]

[Examples] Next, examples of the present invention will be described together with comparative examples.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

Note 1) The aluminum plate has a thickness of 1.0 mm.
Note 2) Al plate cleaning is performed at 10A/d in 5% NaOH aqueous solution.
m2 × 2.0 seconds of electrolysis. Note 3) The plating film for chemical conversion treatment was applied by electroplating. Note 4) Contact with air and water is by spraying (air and water are a mixture of air and water, and water vapor has a dew point of 23 to 80°C). Note 5) Zinc nitrate aqueous solution is Zn(NO3)・6H2
The main component was O, with trace amounts of HNO3 and Fe+++ added. Note 6) To measure the amount of oxide, dissolve the plating layer with a 5% iodine methanol solution, and mix the extraction residue with a mixed flux (boric acid 1,
After dissolving with sodium carbonate 3), it was made into a solution with hydrochloric acid and the amount of zinc was measured by ICP (infrared spectroscopy). Further, regarding the amount of oxygen obtained from GDS (glow discharge spectroscopy) analysis of the surface, the value of the integrated intensity for 1 second from the outermost surface was defined as the oxygen intensity of the oxide film. Note 7) Welding conditions are as follows.

1) Electrode pressure: 250 kgf2) Initial pressure: 40 cycles 3) Current application time: 8 cycles 4) Holding time: 2 cycles 5) Welding current: 15KA 6) Electrode tip shape: Tip diameter 5.0φ (CF 7) Electrode tip material: Cu-Cr (commonly used) 8) Electrode tip life end point determination: Maximum number of dots that can ensure a nugget diameter of 4.0 mm at welding current.

[0023] Welding was performed by placing two aluminum plates one on top of the other with one side facing up and the other side facing down, and performing continuous welding. Note 8) Judgment of chemical conversion treatment is performed using SD5000 (manufactured by Nippon Paint Co., Ltd.) as a chemical conversion treatment solution (zinc-phosphoric acid-fluorinated treatment bath), degreasing and surface conditioning as prescribed, and then applying chemical conversion treatment. evaluated. The evaluation method is SEM (secondary electron beam image)
Those in which the coating was uniformly formed were marked with an ○ mark as passing, and the others were marked with an x mark as failing.

[0024]

[Effects of the Invention] By doing so, the spot weldability of the Al plate can be significantly improved, and the chemical conversion treatment properties can also be improved, which brings about great industrial effects.

Claims (3)

[Claims] 1. An aluminum plate or aluminum alloy plate with excellent spot weldability, characterized in that a plating film for chemical conversion treatment is formed on the surface of the aluminum plate or aluminum alloy plate, and an oxide film is formed on the film layer. . [Claim 2] Spot welding characterized by forming a plating film for chemical conversion treatment on the surface of an aluminum plate or an aluminum alloy plate, then heat-treating the plate, and then bringing it into contact with a steam/water mixture or steam to form an oxide film. A method for manufacturing aluminum plates or aluminum alloy plates with excellent properties. 3. A plating film for chemical conversion treatment is formed on the surface of an aluminum plate or an aluminum alloy plate, and then an oxide film is formed by contacting with an aqueous zinc nitrate solution or electrolytically treating the plate in the aqueous solution. A method for manufacturing aluminum plates or aluminum alloy plates with excellent spot weldability.