To the VAF brain trust: my curiosity is piqued with this question.

Some replacement fuel tank ribs I ordered not long ago came out of the box with almost every part having a bright side and a “dull” side which also showed an interesting hatch mark pattern. Some even had an interesting smoke-type pattern in the material (hopefully it’s discernible in the picture).

Any idea how this happens and does it affect the parts usability? Is it simply artifacts from the material’s manufacturing process? Perhaps caused during forming? A weird type of corrosion I’m not familiar with?

Enlighten me! Thanks in advance.
 

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I am going to guess it has been heat treated after forming. But I stand to be corrected.
Looking at your photo, it seems like someone may have cleaned up the parent sheet of aluminum with Scotchbrite or similar. What does it look like in person?

OTOH, I'd ignore it and build on, unless I had specific concerns!
 
Looking at your photo, it seems like someone may have cleaned up the parent sheet of aluminum with Scotchbrite or similar. What does it look like in person?

OTOH, I'd ignore it and build on, unless I had specific concerns!
I bet you're right. That's about what it looks like.

I've never pulled a part from Van's like this hence why I found it so interesting.

Thanks for your input!