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Fresh machined aluminum looks like its galvanized?

2006

While doing some machining on cast aluminum wheels I have come across a problem. The parts are coming out after machining looking like they are water spotted. I am told that it is called a galvanic occurrence. (looks a lot like galvanized metal)

I'm wondering if:

1. I am doing something to cause this. To slow a speed, too fast, the item is getting too hot, etc.

2. The source material is old and of poor casting.

3. Wrong bit in the CNC machine.

4. Wrong or worn out cutting coolant?

Anyone have experience with this? Any suggestions on who to contact that might shed light on eliminating or reducing this effect.

 

It's a Hass CNC machine and we have used carbide, ceramic and diamond tips. The diamond seems to destroy itself rather quick and the bits are a little over $100 a shot so its gets pricey just running this machine.

FWIW the base metal is old (over 40 years). I suspect it might be the metal but I want to be able to rule out the fact that I might be causing it.

Thanks In advance --

Karl Kirchner
Auto restoration - Inamn, South Carolina