Why the vast majority of aluminum die castings can not do sulfuric acid anodized color processing?

 First, the sulfuric acid anodic oxidation of aluminum alloy material restrictions:

1, the existence of alloying elements will reduce the quality of the oxide film, under the same conditions, in the pure aluminum oxide film obtained the most thick, the highest hardness, the best corrosion resistance, the best uniformity. Aluminum alloy material, in order to get a good oxidation effect, to ensure that the aluminum content, usually, not less than 95% better.

2, in the alloy, the copper will make the oxide film reddish, destroy the electrolyte quality, increase the oxidation defects; silicon will make the oxide film gray, especially when the content of more than 4.5%, the impact is more obvious; iron because of its own characteristics, Anodic oxidation will occur in the form of black spots.

Second, the commonly used die-casting aluminum alloy of the main classification and composition:

(ADC1, A413.0, etc.), YL104 (ADC3, A360); the second is aluminum-silicon-copper alloy, which mainly contains YL112 (ADC1, A413.0, etc.), YL104 (ADC3, A360) A380, ADC10, etc.), YL113 (3830), YL117 (B390, ADC14) ADC12, etc .; Third, aluminum and magnesium alloy, including 302 (5180, ADC5, ADC6).

For aluminum-magnesium alloys, it is oxidizable and colored, which is an important feature of the difference with other alloys; but in comparison, there are also some drawbacks.

1, anodic oxide film with dual nature, and the larger pores, uneven distribution, it is difficult to achieve the best anti-corrosion effect;

2, magnesium has a hardening and brittleness, reduce the elongation, increase the tendency of hot cracking, such as ADC5, ADC6, etc., in the production, because of its wide range of solidification, shrinkage tendency, often produce shrinkage and cracks, casting performance Very poor, therefore, in its use of the scope of a greater limitation, the structure of a slightly more complex of the workpiece, should not be produced;

3, the market commonly used aluminum-magnesium alloy, because of its complex composition, aluminum purity is too low, sulfuric acid anodized, it is difficult to produce a transparent protective film, mostly milky white, color state is poor, according to the normal process is difficult to achieve the desired results.

It can be seen that the commonly used die-cast aluminum alloy is not suitable for sulfuric acid anodic oxidation; however, not all die-cast aluminum alloys can not achieve the purpose of oxidation color, such as aluminum manganese cobalt alloy DM32, aluminum manganese magnesium alloy DM6, Die-casting performance and oxidative performance is superb, just because the time to enter the domestic short, not popular.