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Hi Benjamin, you definitely chose one of the more difficult materials to anodize, A380 has high levels of silicon. The addition of silicon makes the metal flow easier during casting but makes it challenging to anodize. Best case is that you will have a dull gray finish, worst case it will be blotchy in random areas. So in short, anodizing might worsen the appearance of the part.

[Benjamin]

Hi, I have a project making use of aluminum A380 as the base material. I want to coat some of the parts with either type II or III clear anodizing and other parts with a chem finish. My questions are as follows; if I anodize the part, will the coating be visible? Secondly, if I go with a chem finish will this affect how well an adhesive can stick to the part? I am specifically looking at 3M’s DP125 or PU 8609 adhesives.

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[Alexander Brown]

Hi Benjamin, you definitely chose one of the more difficult materials to anodize, A380 has high levels of silicon. The addition of silicon makes the metal flow easier during casting but makes it challenging to anodize. Best case is that you will have a dull gray finish, worst case it will be blotchy in random areas. So in short, anodizing might worsen the appearance of the part.

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[Benjamin]

Thank you for the response Alexander, I primarily chose A380 because of its excellent die casting properties. It is disappointing that it has such a poor result with anodizing. What is the reason for the swirling patterns?

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[Alexander Brown]

Silicone does not anodize so when the part is cast there might be uneven distribution of silicone on the surface of the part, especially if the casting quality is poor. So during anodizing, the areas with increased silicon content will be a different color from the areas with pure aluminum. Note that even though Type II anodizing is considered clear it does slightly change the color of the base metal so the poorly anodized areas will be obvious. Also Type III anodizing is much darker due to it being a thicker coating, so the swirling effect might be even more obvious with type III anodizing. 

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[Daniel Walsh]

Alexander is correct about the potential for a poor appearance, but it all depends on the quality of the casting and subsequent anodizing. Your best option is to request some sample material from the company that will cast your part and have it anodized to see the result, but A380 is notoriously difficult to anodize. In terms of the Chem coat, I assume you mean chromate coating? These coatings are generally cheaper than anodizing and will tend to leave the part with a slight yellow tinge. Chromate coatings are often used as a primer for painting as it has excellent adhesive properties. So I would assume that they will also give excellent bond strength for the adhesives you have mentioned. Note that A380 is also known to produce a spotty appearance after chromate coating, due to the same reasons mentioned by other users.

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