JPH0617288A - Laminated plated aluminum sheet excellent in spot weldability - Google Patents

Abstract

PURPOSE:To manufacture a laminated plated Al sheet excellent in spot weldability by forming a zinc substitution plated layer on the surface of a base metal, forming one or more electroplated layer thereon and specifying the m.p. and coating weight of the topmost surface plated layer. CONSTITUTION:An Al sheet (such as 5000 series) is used as a base metal, and on the surface of this base metal, the zinc substitution plated layer as a primary layer is formed by using a basic zinc substitution plating bath. Next, the surface of this plated layer is applied with one or more electric plated layers to regulate the m.p. of the topmost surface plated layer to 500 deg.C or higher and the coating weight into 1 to 40g/m<2>. Moreover, as the plating having 500 deg.C or higher m.p., the alloy plating of Zn with Ni, Fe, Co, Mn or the like is used, and as the high m.p. plating, the plating of the metals such as Fe, Ni, Cr, Co and Ti or their alloys is used. In this way, the laminated plated Al sheet or Al alloy sheet excellent in corrosion resistance after coating and the adhesion of the plated film as well as excellent in spot weldability can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated aluminum or aluminum alloy plate, and more particularly to an aluminum or aluminum alloy plate suitable for use in a vehicle body or the like assembled by spot welding. .

[0002]

2. Description of the Related Art In recent years, automotive materials have been increasingly required to have anticorrosion measures by spraying an antifreezing agent in cold regions and lightening measures for improving fuel efficiency, such as zinc plating and zinc alloy plating ( Hereinafter, the use of surface-treated steel sheets such as "zinc-based plating"), high-tensile steel sheets, etc. is being promoted. In automobile body manufacturing lines that use such steel sheets, they are formed into a predetermined shape by press working and assembled by resistance welding (spot welding) to assemble each part.
Thereafter, zinc phosphate treatment, electrodeposition coating, and spray coating are generally applied.

On the other hand, recently, aluminum or aluminum alloy plates (hereinafter referred to as "Al
"Plates" are collectively used for car bodies.

The Al plate is generally used in combination with a steel material. In this case, it is desirable to manufacture a part by also using a steel material processing line without newly establishing another manufacturing line for Al plate processing. This is because the cost of installing new equipment can be saved and process continuity can be maintained.

However, for example, when the plated steel sheet and the Al sheet are treated on the same line, the following problems occur in the zinc phosphate treatment step. That is, when the zinc phosphate treatment is applied to the Al plate, not only a good zinc phosphate film is not formed on the Al plate surface, but also the Al plate surface is dissolved and Al ions are eluted in the zinc phosphate treatment bath. Will end up. As a result, the Al ion concentration in the zinc phosphate treatment bath was only a few ppm.
However, even if the above condition is satisfied, a good zinc phosphate treatment film is not formed on the steel plate surface.

As a method for solving the above problems, the present applicant has previously developed an "Al plate excellent in zinc phosphate treatment" and filed a patent application therefor (Japanese Patent Laid-Open No. 61-157693). ). That is, by forming either a zinc plating layer, a zinc alloy plating layer, or an iron alloy plating layer on the surface of the Al plate with an adhesion amount of 1 g / m ² or more, it becomes It is possible to prevent the elution of Al ions from the Al plate, and thereby to form a good zinc phosphate film on both the steel plate and the Al plate even when they are alternately processed in the same line.

Compared with a steel plate, the Al plate has a high electric conductivity and a high heat transfer coefficient, and a strong oxide film is easily formed on the surface thereof, so that the spot weldability, particularly the continuous spotting property is poor.

In the case of a steel sheet, continuous spot welding of 3000 points or more is possible, whereas in the case of an Al sheet, only 300 to 500 points are capable of continuous spot welding. Therefore, when an Al plate is used, it is necessary to stop the line and polish or replace the electrode after every 300 to 500 continuous spots, which significantly reduces the production efficiency.

The zinc-plated Al sheet disclosed in Japanese Patent Laid-Open No. 61-157693 has an improved weldability up to a continuous welding point of about 800 to 1000 points, but does not have a continuous welding point comparable to that of steel sheets. I can't. Therefore, as a measure for improving the spot weldability, the invention of Japanese Patent Laid-Open No. 3-146693 has been proposed.
That is, as the lowermost layer on the surface of the Al plate, displacement plating is carried out in an acidic chloride bath containing hydrofluoric acid, or electroplating is carried out in a sulfuric acid acidic bath to form a Ni (nickel) plating layer, and It is an invention that zinc-based plating is applied to.

However, it has been found that when the method disclosed in Japanese Patent Laid-Open No. 3-146693 is actually applied, the following three major problems occur. First, as shown in the example of the publication, the continuous hitting point is improved to only about 1300 points at most. This is because when the surface layer is plated with a low melting point metal such as zinc, the low melting point metal of the plating layer diffuses into the electrode and forms a brittle alloy with copper, which is the main component of the electrode, to promote wear of the electrode tip. Is.

Secondly, in general, a material for an automobile body is required to have corrosion resistance after painting as one of its performances, particularly corrosion resistance when a coating film has a flaw after painting.
In the Al plate disclosed in JP-A No. 2003-242242, the adhesion between the first Ni plating layer and the Al base material is poor, and sufficient corrosion resistance cannot be obtained. Al is an electrochemically base metal, and is easily ionized.
On the other hand, Ni is a precious metal and is difficult to ionize. When these two metals come into contact with each other, Al serves as an anode (anode) and Ni serves as a cathode (cathode) to form a galvanic cell, and Al is ionized and eluted. Therefore, the base material (Al) and plating layer (Ni)
Delamination occurs between and, and the zinc-based plating layer and the coating film on the Ni plating layer float up to form blisters.

Thirdly, when an Al plate plated with a zinc-based plating on a Ni plating layer was press-molded, Ni pieces that were separated during the deformation process dig into the Al base material due to Ni being hard, and this was the cause. The stress concentrates on the notch, which causes cracks and breaks of the plate.

[0013]

DISCLOSURE OF THE INVENTION The present invention provides a surface-treated Al plate which is excellent in corrosion resistance after coating and adhesion of a plating film, and has spot weldability close to that of a zinc-based plated steel plate. That is the purpose.

[0014]

The gist of the present invention is to have a first layer of zinc-based displacement plating formed on the surface of a base material and one or more electroplating layers formed thereon, The outermost plating layer has a melting point of 500 ° C. or more and an adhesion amount of 1 to 40 g / m ² and is a laminated plated aluminum plate or aluminum alloy plate excellent in spot weldability ”.

The Al plate as the base material is, for example, 1000 series, 5000 series.
Series, 6000 series, mainly used for car body. The first layer of zinc-based plating is Zn plating, Zn and N
Replacement plating of alloys such as i, Fe, Co, Cr and Mn. There is one or more upper plating layers on the first layer, but the plating of the outermost layer must be a metal or alloy plating having a melting point of 500 ° C or higher.

As described above, it is essential that the lowermost layer in contact with the surface of the base material has a zinc-based displacement plating layer and the outermost layer has a plating layer with a melting point of 500 ° C. or higher. Layers may be present. It is essential that the plating layer having a melting point of 500 ° C. or more is the outermost layer, as will be understood from the weldability improving mechanism described later.

[0017]

The Al plate of the present invention has a zinc-based displacement plating layer as the first layer on the surface of the base material. This layer is applied by degreasing the base Al plate by a general method and then treating it in a basic zinc-based displacement plating bath. Al is an amphoteric metal and the oxide film dissolves under basic conditions, causing a substitution reaction with zinc or a zinc alloy in the bath on the surface of fresh metal Al, which results in a strong metal-metal bond and high adhesion of zinc or A zinc-based alloy plating layer is formed. The basic zinc-based displacement plating bath is
From the viewpoint of operability and economy, it is desirable that the material contains sodium hydroxide, zinc oxide, and an oxide salt or hydroxide salt of an alloy component. Further, the displacement plating of the first layer is performed by performing displacement plating once, then dissolving and removing the plating layer in an aqueous nitric acid solution or an aqueous sulfuric acid solution, and then performing the displacement plating again twice or more. Layers are formed and their performance is even better.

The corrosion resistance and coating adhesion after coating are governed by the formation of galvanic cells, as described above. When the first layer is zinc-based plating as in the Al plate of the present invention, the galvanic current is dispersed because the potentials of Al and this zinc-based plating are close to each other. That is, the galvanic current that has been entirely flowing between the Al base material and the plating layer of the first layer is replaced with the galvanic current between the plating layers of the second and subsequent layers. As a result, the galvanic current between layers is reduced as a whole and delamination is eliminated. This greatly improves the corrosion resistance after coating and the adhesion of the coating film.

Also in press forming, zinc is soft, and zinc-based alloys generally form intermetallic compounds and exhibit a self-lubricating action due to their brittleness. Therefore, in the laminated plated Al plate of the present invention, Unlike an Al plate having Ni plating as the first layer, a hard Ni peeling piece does not bite into the Al base material to form a notch, and the base material does not break during press molding at all.

On the other hand, the present inventor has sought a concrete method for preventing electrode wear during spot welding and improving continuous dot-forming property. As a result, by providing a plating layer having a high melting point with a thickness of a certain level or more on the outermost layer of the Al plate on which the displacement plating of the first layer described above is performed, the metal of the plating layer becomes an electrode during spot welding. It was confirmed that the alloy does not diffuse into the alloy to form a brittle alloy, wear of the tip of the electrode is reduced, and continuous dot performance is remarkably improved.

The Al plate of the present invention has at least one plating layer on the displacement plating layer. The outermost layer of the plating has a melting point of 500 ° C. or more and an adhesion amount of 1 g / g. It is a plating layer of m ² or more. The melting point of this plating layer is
If the temperature is lower than 500 ° C, the metal of the plating layer diffuses into the electrode during welding to form the brittle alloy as described above, and the wear of the electrode tip becomes serious.

As the plating having a melting point of 500 ° C. or higher, zinc-based plating includes alloy plating of Zn and Ni, Fe, Co, Cr, Mn or the like. For higher melting point plating, Fe, Ni, Cr,
There is plating of metals such as Co and Ti and alloys thereof.

When the amount of the above-mentioned plating having a melting point of 500 ° C. or more is less than 1 g / m ² , the plating layer is melted and removed during spot welding, and the effect of providing this layer as the outermost layer is not recognized. However, even if the adhesion amount is more than 40 g / m ² , the effect of improving the weldability is almost unchanged and only the manufacturing cost increases.

The plating layer having a melting point of 500 ° C. or higher may be provided directly on the above-mentioned displacement plating layer, but another plating layer may be provided between them. In the case of performing the laminated plating of three layers or more, if zinc plating or zinc alloy plating is used as the intermediate layer, the effect of improving the corrosion resistance is further enhanced.

[0025]

EXAMPLES The effects of the present invention will be described below with reference to examples.

5000 series Al plate (1 mm thickness, 100 mm x 150 mm)
Using the above as a base material, the following processes were performed to produce plated Al plates shown in Table 1.

(A) Plating of the first layer (basic zinc-based alloy displacement plating) Zinc oxide is dissolved in an aqueous solution of sodium hydroxide (concentration: 300 to 600 g / liter) in an amount of 10 to 200 g / liter to prepare an alloy component. The metal salt in the form of oxide or hydroxide is 0 to 100 g /
Liter was added. The treatment liquid temperature was set to 10 to 50 ° C., and the amount of adhesion was controlled by the reaction time.

(B) Plating for the second layer and thereafter Plating bath: Sulfate bath (pH 1.5 to 2.5). The bath composition is adjusted to be the plating composition shown in Table 1. Bath temperature: 50-60 ° C Current density: 20-100 A / dm ² Corrosion resistance, press formability and after-coating of the Al plate obtained by the above treatment Spot weldability was evaluated by the following method.

(A) Corrosion resistance after coating Cationic electrodeposition coating (thickness: 20 μm) and spray coating with melamine alkyd coating on a plated Al plate (twice coating.
(Thickness: 35 μm each), a cross cut was put on the surface, and the complex corrosion test of the cycle shown in FIG. 1 was carried out for 30 cycles, after which the blister width of the cut part was measured.
The evaluation criteria are as follows.

1: Blister width is less than 0.5mm (pass) 2: Blister width is 0.5mm or more and less than 1.0mm (pass) 3: Blister width is 1.0mm or more and less than 2.0mm (fail) 4: Blister width is 2.0mm or more and less than 3.0mm (fail) 5: Blister width is 3.0mm or more (fail).

(B) Adhesion of plating film (press formability) The plated Al plate was bent back, an adhesive tape was attached to the bent part to peel it off, and the adhesion was evaluated by the amount of metal pieces of the plating film peeled off. did. The evaluation criteria are as follows.

◯: Almost no peeled pieces are seen. Δ: The peeled pieces adhered to the tape at an area ratio of 10 to 50%. X: The peeled pieces adhere to the tape at an area ratio of more than 50%.

(C) Spot Weldability Evaluated under the following continuous spot welding conditions.

Current: 27,000 A Pressurization force: 300 kgf Energization time: 6 cycles (at 60Hz) Electrode shape: Dome type Welding method: "1 point / 2 seconds after 20 points continuous welding, rest for 40 seconds or more" This cycle is repeated. Three shear test pieces were sampled for every 100 points, and a tensile test was performed to determine the number of continuous welding points until the shear load of the welded portion did not satisfy 200 kgf.

Criteria: Goods satisfying a predetermined shear load of 1500 points or more are considered good.

The above evaluations are summarized in Table 1. In Comparative Example 1 of Table 1, the first layer is not subjected to displacement plating, and only zinc electroplating is performed. Naturally, all properties are inferior. In Comparative Example 2, the outermost layer plating is pure zinc having a low melting point, and in Comparative Example 3, the outermost layer has a insufficient amount of plating adhered. Since Comparative Example 4 does not have the displacement plating layer (first layer), it is particularly inferior in corrosion resistance after coating and adhesion to the plating film.

Those corresponding to the examples of the present invention are satisfactory in all properties including weldability, and particularly those having an intermediate layer plating have remarkably improved corrosion resistance after coating. In addition, what was mentioned as a prior art example uses the above-mentioned Ni plating as a 1st layer. Although this has a slightly improved weldability, it is not suitable for press molding because it is significantly inferior in corrosion resistance after painting and has poor film adhesion.

[0038]

[Table 1 (1)]

[0039]

[Table 1 (2)]

[0040]

As shown in the examples, the plated Al sheet of the present invention is excellent in corrosion resistance after coating and adhesion of the plating film. Also, the problem of Al ion elution does not occur even in the zinc phosphate treatment step. Moreover, since it is also excellent in the continuous spotting property of spot welding, it is extremely useful as a material for automobiles for which weight reduction is a problem.

[Brief description of drawings]

FIG. 1 is a diagram illustrating steps and test conditions of a complex corrosion test.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Ikeda 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries, Ltd. (72) Inventor Takao Aibu 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd. (72) Inventor Keizo Namba 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd.

Claims (1)

[Claims] 1. A zinc-based displacement plating layer formed on the surface of a base material, and one or more electroplating layers formed on the first layer. The outermost plating layer has a melting point of 500 ° C. The laminated plating aluminum plate or aluminum alloy plate having excellent spot weldability, characterized in that the adhesion amount is 1 to 40 g / m ^{2 as} described above.