Why do self tapping screws for aluminum have oxidized spots?

Mr. Chen of Jiangsu gave us self tapping screws for aluminum 2 months ago and asked if we can make aluminum 7075, 100000pcs, 4*12 pan head phillips self tapping screws.

We can also produce 7075 aluminum. After asking about Mr. Chen’s request for the surface, Mr. Chen asked the self tapping screws for aluminum salt spray test to reach 12 hours.

self tapping screws for aluminum can be used for salt spray testing, but they must be oxidized first, and oxidized spots will appear. Ask Mr. Chen if he can accept it. Mr. Chen said that this aluminum screw is not used for surface assembly. It is used inside the product and can accept oxidized spots on the surface of aluminum screws.

If you want to customize self tapping screws for aluminum, +long +screw +supplier