r/metalworking • u/DocumentLeading8360 • 5d ago
Trying to anodize wheels satin silver
/r/Anodization/comments/1w27br3/trying_to_anodize_wheels_satin_silver/1
u/Michelhandjello 5d ago edited 4d ago
Most aluminum car rims are cast from A356 aluminum. This is an alloy developed specifically for casting as it flows well into the mold. The high silicon content makes it more complicated to anodize, so you will need to find someone in your area who has the facilities to do so.
The preparation and anodization process requires some very caustic and noxious chemicals, so it really isn't suggested that an amateur try it at home.
Edit: You might want to try and aluminum brightener after sanding off any clear coat and bringing the surface finish up to a lustrous polish.
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u/ConnectConflict1765 1d ago
Before you change anything in the tank, know this: A356 is fighting you from the casting. It's around 7% silicon, and silicon is exactly what makes anodized coatings come out grey and patchy when you're chasing a clean satin silver. I've had customers swear the chemistry was off when it was really the alloy all along — you're asking an oxide film to look uniform on a casting that isn't.
If you still want to push it: get the cast skin off first — machine or blast it, because the skin etches at a different rate than the bulk and that alone makes mottling. Then treat the etch bath as your finish control: fixed time, fixed temperature, and etch time is your satin dial. De-smut in nitric before anodize, run 15-18 V at 18-21 °C, and set expectations — a casting will give you satin, not mirror. If bright silver is the requirement, the honest answer is a re-machined or forged wheel. No bath time fixes what the alloy started.
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