Aluminum certified as the same etches differently

Q. I have some parts that when we etch them are coming up different colors. Some with no change and others more to the darker almost black side. Customer has material certs stating they are all 6061 material.

61731-1dtl 61731-1

Now I know that the color change will denote some sort of alloy change or change in the chemical makeup of the alloy as the 2xxxa and 7xxx will etch more blackish in color and 6xxx series generally has a very minimal color change when etching. Any ideas of why if they are all the same are we getting different looks. You can even see the difference once they are anodized and dyed.

Michael Pecjak
- Mentor Ohio
September 10, 2024

Michael

It is probable that the machinist didn't check or verify the material that was pulled from stock before machining it. Being a turned parts, he should have noticed the difference in the chips/swarf. They are not all from the same heat lot nor of the same alloy.

Willie Alexander
- Green Mountain Falls, Colorado

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