JPH0570970A - Al-mg based alloy material excellent in phosphating treatment - Google Patents

Abstract

PURPOSE:To provide a Al-Mg based alloy material excellent in filiform corrosion resistance (corrosion resistance post coating) after phosphating treatment by providing the Al-Mg based alloy material excellent in phosphating treatment used for a field such as a panel material for various vehicle such as automobile, an outside plate material for household electric goods and a building material which are used for coating after machining such as press forming and chemical treatment such as phosphating treatment. CONSTITUTION:When an oxide layer is formed on the base material surface of the Al-Mg based alloy thickness of the oxide layer is <=70Angstrom and Mg conc. in the oxide layer is <=20 atom %.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to panel materials for various vehicles such as automobiles, outer panel materials for household electric appliances, building materials, etc., after processing such as press molding and chemical conversion treatment with phosphate, etc. The present invention relates to an Al-Mg based alloy material having excellent phosphating property, which is used in the field of coating and use.

[0002]

2. Description of the Related Art Since Al or Al alloy material (hereinafter abbreviated as Al alloy material) is lightweight and has excellent corrosion resistance and designability, it is used as an outer panel material for household electric appliances and a construction material. Widely used in the field.

Recently, Al alloy materials have come to be used also in the field of vehicles such as automobiles for the purpose of reducing the weight of vehicle bodies. Among them, Al-Mg alloy sheets are excellent in press formability and are used as body materials for automobiles. It is used.

However, since the surface of the Al alloy material is covered with a stable oxide film, it is inferior to the conventional steel sheet and surface-treated steel sheet in the phosphate treatment property of the pretreatment for coating, and as a result, the coating film adhesion is poor. Also, there was a problem that the corrosion resistance after coating was not sufficiently improved.

Therefore, for the purpose of improving the phosphating property of the Al alloy material, a method is proposed in which the amount of F ⁻ ions added to the phosphating solution is increased to increase the etching amount of Al. Has been done. However, the Al
In the case of a Mg-based alloy material, even if this method is used, a sufficient effect is not exhibited, and in some cases, the phosphating property is deteriorated, and there is a problem that the quality stability is lacking. There is.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an Al-Mg alloy material having excellent phosphating property, which can be used after phosphating. It is intended to provide an Al-Mg alloy material having good thread rust resistance (corrosion resistance after coating).

[0007]

Means for Solving the Problems According to the present invention which has achieved the above object, the thickness of an oxide layer formed on the surface of a base material of an Al--Mg alloy is 70 Å or less, The gist is that the Mg concentration is 20 atomic% or less.

[0008]

The present inventors have conducted extensive studies to improve the phosphatability of the Al-Mg alloy material, and as a result, the phosphatability of the Al-Mg alloy material is It has been found that the difference greatly depends on the properties of the oxide layer to be formed and that it depends on the thickness of the oxide layer and the Mg concentration in the oxide layer.

The thickness of the oxide layer must be 70 Å or less, preferably 20 to 50 Å. If it is too thick, the etching of the Al-Mg based alloy in the phosphate bath is suppressed, and the phosphate treatment property deteriorates.

Further, the Mg concentration in the oxide layer must be 20 atomic% or less, and more preferably 10 atomic% or less. When the above Mg concentration is too high, when it is immersed in the phosphating solution, it reacts violently to increase the amount of hydrogen generated, and as a result, the adhesiveness of the phosphate film deteriorates. Incidentally Mg
As a method of controlling the concentration to 20 atomic% or less, for example, a method of immersing an Al-Mg-based alloy material having an oxide layer formed in a dilute inorganic acid solution of nitric acid to preferentially elute the Mg component is used. You can use it.

As the above Al-Mg alloy material, S
1 of elements such as i, Mn, Cu, Zn, Pb, Cr and Ni
Various Al-M containing two or more species as synthetic components
A g-based alloy can be applied. Further, the shape is not limited to the plate-like object, and can be applied to various shapes such as a rod-like object, a linear object, and a tubular object according to the application and purpose.

[0012]

Example Using an Al-Mg-based alloy material obtained by aging treatment and immersion treatment (pretreatment) in an acidic solution or an alkaline solution using a rolled plate made of an Al-Mg-based alloy shown in Table 1,
The thickness and Mg concentration of the oxide layer formed on the surface were measured by AES analysis, and the phosphate treatment property and the yarn rust resistance were examined by the following methods. The results are also shown in Table 1. Each Al-M
The pretreatment method for the g-based alloy material was as shown in Table 2.

Phosphate treatability: Evaluation was made by the coverage rate of the phosphate film after the phosphate treatment was performed for 2 minutes using a commercially available immersion type phosphate treatment solution. [Evaluation Criteria] O: Film coverage of 90% or more B: Film coverage of 80 to 90% X: Film coverage of less than 80% Thread rust resistance: Phosphate treatment followed by electrodeposition coating and spray coating tests A cross cut was put in one piece, and the length of the thread rust from the cross cut portion generated when the following corrosion test was carried out for 8 cycles was evaluated.

[Corrosion test] Salt spray test (35 ° C x 24h) ↓ Wetting test (80% RH, 50 ° C x 120h) ↓ Indoor exposure (RT x 24h) [Evaluation criteria] ○ ... Thread rust length 1mm or less △ … Thread rust length 1-2 mm ×… Thread rust length 2 mm or more

[0015]

[Table 1]

[0016]

[Table 2]

Nos. 1 to 4 are examples according to the present invention,
The Mg component is preferentially eluted by the pretreatment with the inorganic acid solution and the Mg concentration in the oxide layer is sufficiently lowered, so that the phosphate treatment property is good and the yarn rust resistance is excellent. On the other hand, Nos. 5 to 9 are comparative examples in the case where one or more of the conditions according to the present invention are not satisfied, and since the alkaline aqueous solution is used for the pretreatment, the elution of the Mg component is insufficient and the oxide layer The content of Mg is high, and the phosphate treatment and the yarn rust resistance are insufficient.

[0018]

EFFECTS OF THE INVENTION Since the present invention is constructed as described above, the coating property represented by the thread rust resistance is improved by improving the phosphate treatment of the Al-Mg alloy material excellent in press formability. It has become possible to provide an Al-Mg alloy material having excellent post-corrosion resistance.

Claims (1)

[Claims] 1. The thickness of an oxide layer formed on the surface of a base material of an Al--Mg alloy is 70 Å or less, and M in the oxide layer is
An Al-Mg-based alloy material excellent in phosphatability, characterized in that the g concentration is 20 atomic% or less.