FOP32 Melt down?????

[Monaco]

I've noticed this on a few of my HSFs. After reading this thread, I started sanding off the black anodizing gunk on a new, unused Al heatsink. I'm not lapping yet, just removing that black crap.

I got it all off and now I can clearly see that weird discoloration effect right where the CPU would be if it was ever used. It is an irregular oval, perhaps 2cm across.

I don't know what this means, quite. My best guess is that it has something to do with the manufacturing process to start with. The cool electro-chemical stuff mentioned above seems unlikely IMHO as this seems to occur inside the 'sink, not just the surface.

But hey, I ain't no metallurgist or chemist or anything, so use that grain of salt.

-the monster

 

[Tiger]

Having spent some hours trying to get this off without making any real progress I thought I would try some chemistry. I diluted 5ml of vinegar (dilute acetic acid) in 3L of water and emersed the HS in it. There was lots of bubbling from the area of the imperfections and when removed they were gone. Has got to be an oxide of Al. By the way I take no responsibility for any heatsink that you try this on. Bear in mind Al is very reactive.