JP2706597B2 - Laminated plated aluminum plate with excellent spot weldability - Google Patents

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 an automobile body assembled by spot welding. .

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for materials for automobiles to take measures against corrosion by spraying a deicing agent in cold regions and measures to reduce weight for improving fuel efficiency. The use of surface-treated steel sheets such as “zinc-based plating”), high-strength steel sheets, and the like has been promoted. In a car body manufacturing line using such steel sheets, the parts are formed into a predetermined shape by press working, and each part is assembled by resistance welding (spot welding).
Thereafter, it is generally applied with zinc phosphate treatment, electrodeposition coating and spray coating.

On the other hand, recently, a plate of aluminum or aluminum alloy (hereinafter referred to as “Al
Boards) are increasingly used for vehicle bodies.

[0004] Generally, an Al plate is used in combination with a steel material. In this case, it is preferable to manufacture a part by also using a steel material processing line without newly establishing another production line for processing an Al plate. This is because the cost of new equipment can be saved and the continuity of the process can be maintained.

[0005] However, for example, when the above-mentioned plated steel sheet and Al sheet are processed in the same line, the following problems occur in the zinc phosphate processing step. In other words, when zinc phosphate treatment is applied to an Al plate, not only is a good zinc phosphate film not formed on the surface of the Al plate, but also the surface of the Al plate is dissolved, and Al ions are eluted into the zinc phosphate treatment bath. Would. As a result, the concentration of Al ions in the zinc phosphate treatment bath was only a few ppm.
A good zinc phosphate treatment film is not formed on the surface of the steel sheet even if the surface of the steel sheet is changed.

As a method for solving the above-mentioned problems, the present applicant has previously developed an "Al plate excellent in zinc phosphate treatability" and applied for a patent (Japanese Patent Application Laid-Open No. 61-157693). ). That is, by forming any one of a zinc plating layer, a zinc-based alloy plating layer, and an iron-based alloy plating layer on the surface of the Al plate with an adhesion amount of 1 g / m ² or more, a The elution of Al ions from the Al plate is prevented, so that even when the steel plate and the Al plate are alternately treated on the same line, a good zinc phosphating film can be formed on both.

[0007] Compared to a steel plate, an Al plate has a higher electric conductivity and heat transfer coefficient, and a strong oxide film is easily formed on the surface thereof.

[0008] In the case of a steel sheet, continuous spot welding of 3000 points or more is possible, whereas in the case of an Al plate, only about 300 to 500 points have continuous spotting properties. Therefore, when an Al plate is used, the line must be stopped at every 300 to 500 continuous points to polish or replace the electrode, and the production efficiency is significantly reduced.

The zinc-plated Al plate disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-157693 has improved weldability up to a continuous hitting point of about 800 to 1000 points, but has a continuous spotting weldability comparable to that of a steel sheet. I can't. Therefore, as a measure for improving the spot weldability, the invention of Japanese Patent Application Laid-Open No. 3-146669 has been proposed.
That is, as the lowermost layer on the surface of the Al plate, a Ni (nickel) plating layer is formed by displacement plating in an acid chloride bath containing hydrofluoric acid or by electroplating in a sulfuric acid bath. Of the present invention is to apply zinc-based plating to the steel.

However, it has been found that the following three major problems occur when the method disclosed in Japanese Patent Application Laid-Open No. 3-146669 is actually applied. First, as shown in the embodiment of the publication, continuous hitting points can be improved only up to about 1300 points. 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 at the tip of the electrode. It is.

Secondly, in general, a material for an automobile body is required to have corrosion resistance after coating as one of its performances, particularly when a coating film has a flaw after coating.
In the Al plate disclosed in the above publication, the adhesion between the first Ni plating layer and the Al base material is poor, and sufficient corrosion resistance cannot be obtained. Al is originally an electrochemically low metal and is easily ionized.
On the other hand, Ni is a noble metal and hardly ionized. When these two metals come into contact, Al becomes an anode (anode) and Ni becomes a cathode (cathode), constituting a galvanic cell, and Al is ionized and eluted. Base material (Al) and plating layer (Ni)
Delamination occurs between the film and the Ni-based plating layer and the coating film on the Ni plating layer to float and form a blister.

Third, when an Al plate on which a zinc-based plating is applied on a Ni plating layer is press-formed, since the Ni is hard, the Ni pieces peeled off in the process of deformation bite into the Al base material, which is caused. Stress concentrates in the notch, from which cracks occur and the plate breaks.

[0013]

SUMMARY OF THE INVENTION The present invention provides a surface-treated Al plate which has excellent corrosion resistance and coating film adhesion after coating, and has a spot weldability similar to that of a zinc-based plated steel plate. The purpose is to do so.

[0014]

The gist of the present invention is to provide a zinc-based displacement plating first layer formed on the surface of a base material and one or more electroplating layers formed thereon. because the amount deposited in the outermost surface of the plating layer is melting point 500 ° C. or higher for 1 to 40 g / m ²
A laminated plated aluminum sheet or aluminum alloy sheet excellent in spot weldability, characterized in that it is a plated layer (excluding a Zn-Fe-based alloy plated layer) . Said above
The “Zn-Fe-based alloy plating layer” in the introductory text refers to “Fe content
And a Zn-Fe alloy plating layer with a percentage of 5 to 60% by weight. "
Fe content of 5 to 60% by weight and Ni, Co, Cr,
Contains 0.5% by weight or more of one or more of Mn, Sn, and Cu
Zn—Fe-based alloy plating layer ”.

The Al plate as a base material is, for example, 1000 series, 5000
Series, 6000 series, mainly used for automobile bodies. The first layer zinc plating is Zn plating, Zn and N
It is displacement plating of alloys such as i, Fe, Co, Cr, and Mn. On top of this first layer is one or more upper plating layers, the outermost plating of which must be a metal or alloy plating with 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 having a melting point of 500 ° C. or more. Layers may be present. It is essential that the plating layer having a melting point of 500 ° C. or more be the outermost layer as can be seen 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 formed by degreased a base material Al plate by a general method, and then treating it in a basic zinc-based displacement plating bath. Al is an amphoteric metal, and under basic conditions, the oxide film dissolves and causes a substitution reaction with zinc or zinc alloy in the bath on the surface of fresh metal Al, resulting in strong adhesion of zinc or zinc having a strong metal-metal bond. A zinc-based alloy plating layer is formed. The basic zinc-based displacement plating bath is
From the viewpoints of operability and economy, it is preferable that the material contains sodium hydroxide and zinc oxide, and an oxide or hydroxide of an alloy component. Also, the displacement plating of the first layer is performed by performing the displacement plating once, then dissolving and removing the plating layer once in a nitric acid aqueous solution or a sulfuric acid aqueous solution, and repeating the replacement plating twice or more. A layer is formed and its performance is further improved.

The corrosion resistance and coating film adhesion after coating are governed by the formation of galvanic cells as described above. If 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 the zinc-based plating are close to each other. In other words, the galvanic current flowing between the Al base material and the first plating layer is replaced by the galvanic current between the second and subsequent plating layers. As a result, the galvanic current between the layers is reduced as a whole, and delamination is eliminated. As a result, the post-painting corrosion resistance and coating film adhesion are greatly improved.

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. As in the case of an Al plate having Ni plating as the first layer, a hard Ni exfoliated piece does not bite into the Al base material to form a notch, and no base material breakage occurs during press forming.

On the other hand, the present inventor has searched for a concrete method of preventing the electrode from being worn during spot welding and improving the continuous hitting property. As a result, by providing a plating layer having a high melting point to a certain thickness or more on the outermost layer of the Al plate having been subjected to the substitution plating of the first layer described above, the metal of the plating layer becomes an electrode during spot welding. It was confirmed that no brittle alloy was formed by diffusing into the electrode, the wear of the electrode tip was reduced, and the continuous hitting property was significantly improved.

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

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

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

The plating layer having a melting point of 500 ° C. or more may be provided directly on the above-mentioned substitution plating layer, or another plating layer may be provided between them. In the case of performing three or more layered plating, if zinc plating or zinc-based alloy plating is used as the intermediate layer, the effect of improving 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 (1mm thick, 100mm × 150mm)
Was used as a base material, and the following treatment was performed to produce a plated Al plate shown in Table 1.

(A) First layer plating (basic zinc-based alloy displacement plating) 10 to 200 g / liter of zinc oxide is dissolved in an aqueous solution of sodium hydroxide (concentration: 300 to 600 g / liter) to form an alloy component. Metal oxide in the form of oxide or hydroxide from 0 to 100 g /
One liter was added. The temperature of the processing solution was set at 10 to 50 ° C., and the amount of adhesion was controlled by the reaction time.

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

(A) Corrosion resistance after coating Cathodic electrodeposition coating (thickness: 20 μm) on a plated Al plate and spray coating with melamine alkyd paint (twice coating.
(Thickness: 35 μm each), a cross cut was made on the surface thereof, and a composite corrosion test of the cycle shown in FIG. 1 was performed for 30 cycles, and then the blister width of the cut portion was measured.
The evaluation criteria are as follows.

1: Blister width less than 0.5 mm (pass) 2: Blister width 0.5 mm or more and less than 1.0 mm (pass) 3: Blister width 1.0 mm or more and less than 2.0 mm (fail) 4: Blister width 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 applied to the bent portion, peeled off, and evaluated by the amount of the metal piece of the plating film that adhered to the adhesive tape and peeled off. did. The evaluation criteria are as follows.

A: Almost no peeled pieces were observed. Δ: The peeled piece adhered to the tape at an area ratio of 10 to 50%. X: The peeled piece adhered to the tape at an area ratio exceeding 50%.

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

Current: 27,000 A Pressure: 300 kgf Energizing time: 6 cycles (at 60 Hz) Electrode shape: Dome Welding method: "After 20 consecutive spot welding at 1 point / 2 seconds, pause for more than 40 seconds" Is repeated. Three shear test pieces were sampled at every 100 points and subjected to a tensile test to determine the number of continuous hits until the shear load of the weld no longer satisfies 200 kgf.

Judgment criteria: Those satisfying a predetermined shear load of 1500 points or more are judged as good.

The above evaluations are summarized in Table 1. In Comparative Example 1 of Table 1, the first layer was not subjected to displacement plating, and only zinc was electroplated. Naturally, all properties are inferior. Comparative Example 2 is poor in weldability because the outermost layer plating is pure zinc having a low melting point, and Comparative Example 3 is insufficient in the outermost layer plating adhesion amount. Comparative Example 4 is particularly inferior in post-painting corrosion resistance and plating film adhesion because there is no displacement plating layer (first layer).

Those corresponding to the examples of the present invention are satisfactory in all characteristics including weldability, and particularly those having an intermediate layer plating have significantly improved corrosion resistance after painting. It should be noted that the above-described Ni plating is used as the first layer as a conventional example. Although the weldability is slightly improved, the corrosion resistance after coating is remarkably inferior, the film adhesion is poor, and it is not suitable for press molding.

[0038]

[Table 1 (1)]

[0039]

[Table 1 (2)]

[0040]

As shown in the examples, the plated Al plate of the present invention is excellent in corrosion resistance after coating and adhesion of a plated film. Also, there is no problem of elution of Al ions in the zinc phosphate treatment step. In addition, since it is excellent in continuous spot welding property of spot welding, it is extremely useful as a material for automobiles in which weight reduction is an issue.

[Brief description of the drawings]

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

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Masaya Kimoto Inventor 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Inside Sumitomo Metal Industries, Ltd. (72) Inventor Hiroshi Ikeda 5--11 Shimbashi, Minato-ku, Tokyo No. 3 Sumitomo Light Metal Industries Co., Ltd. (72) Takao Aitake 5-11-3, Shimbashi, Minato-ku, Tokyo (72) Inventor Sumitomo Light Metal Industries Co., Ltd. 11-3 Sumitomo Light Metal Industries Co., Ltd. Examiner Mitsuo Teramoto (56) References JP-A-6-73592 (JP, A) JP-A-6-88287 (JP, A)

Claims (1)

(57) [Claims] 1. A zinc-based displacement plating first layer formed on a base material surface and one or more electroplating layers formed thereon, wherein the outermost plating layer has a melting point of 500 ° C. The plating layer with an adhesion amount of 1 to 40 g / m ² (however, Zn-Fe alloy
Laminate plating aluminum plate or aluminum alloy plate is excellent in spot weldability, characterized in that a except come layer).