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FOP32 Melt down?????

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Apr 6, 2001
Perhaps someone has come across this or may be this is a first. Have just removed my FOP32 and it looked a bit rough so I decided to re-lap it. I got half through the process but the area where it was in contact with the proc would not smooth out. Had a look at the surface with a magnifying glass and it looks as though the AL alloy has undergone a meta-physical change as it appears all crystallised;
Any ideas?
Yikes, that is interesting. I have two of these units myself and haven't had this happen, but I haven't lapped them yet either. I would appreciate hearing opinions on this myself.

I'm with the above post. Is it crystal looking or oxidation?

Start lapping again with maybe 320 and get a good layer off of it, then smooth it down with the finer stuff. You "should" be able to get below that layer.
Ah, I remember something like this. Hoot had a post a while back that had to do with AS II crystalizing or so. Perhaps it could be that. Let's see if I can find it
I have been at it with a block using 80, 180 and 320 grit and the area is widening. (5 hours so far)
I have been using ASII.
The actual bumps or imperfections appear to be harder than the aluminium.
Below is a pic of the whole HS.
now that's crazy! seems the deeper you go the further it radiates? I wonder if there's something about using a cheap alum material to make it?

Hoot is good on cooling stuff.......hope he stops by!
Shadow ÒÓ (Jul 27, 2001 04:51 p.m.):
I'm with the above post. Is it crystal looking or oxidation?

Start lapping again with maybe 320 and get a good layer off of it, then smooth it down with the finer stuff. You "should" be able to get below that layer.

Aluminium oxide can take the form of clear crystal as in natural sapphires. I wonder if anyone has some home-brewed method of anodizing to counter this otherwise it'll just happen again after you have cleaned it up.
is that something that is rubbing off of your sandpaper maybe? Thats weird.
i have something like that on my fop32 too

but actually it looks darker and it's at the area where the cpu core is contacting.....

it looks like it's burnt but i m not sure.....plz help

i use something called STARS-700 as thermal paste
according to the package it said to contain 25% silver or something like that....will that affect the heatsink?
William (Jul 28, 2001 03:04 a.m.):
is that something that is rubbing off of your sandpaper maybe? Thats weird.

Yeah, I wonder. You are sanding it wet, right? Normally the problem is clogging the sandpaper, after which it won't do much. That's what the water helps prevent, although with aluminum the abrasive seems to still clog up. But the abrasive particles break off with wear and they could possibly get embedded in the soft aluminum.

Taking off much material with grits above 100 will take forever, but 5 hours of 80 grit should have taken off quite a bit.
I am sanding dry.
Looking at it logically, the area that is worst affected is the area where the oil from the ASII is vaporising on the surface of the HS. I wonder if it is not some kind of oxidation.
This looks like it could be corrosion possibly caused by the ASII. The following can be found at;
Galvanic Corrosion
This type of corrosion occurs when two conducting materials of different chemical composition are joined and exposed to conducting solution e.g. when iron is connected to copper. Iron passes into solution as Fe+2 ions and the residual electrons are conducted through to the copper and as a consequence hydroxyl ions, 0H- , are formed at the surface. Galvanic corrosion is very damaging because it concentrates on the less noble metal at the metal-metal junction, where deep attack occurs. At the junction a large corrosion current can pass because the electrical resistance of the short path through the electrolyte is low.

Common forms of metal joining, e.g. brazing, welding etc. provide junctions at which galvanic corrosion can develop. Galvanic corrosion on a microscopic scale can also occur between constituents of multi-phase alloys and of impure metals which contain foreign particles and intermetallic compounds.

When aluminium is coupled with copper or brass, corrosive attack upon the aluminium is accelerated by these materials in severe or modest atmospheres and conditions of immersion. Contact between aluminium and stainless steel (18/8, 18/8/2 and 13% Cr) will only slightly increase the corrosion of the aluminium in dry atmospheres. However, it is markedly increased in moist atmospheres, particularly in marine conditions.

A simple way of avoiding bimetallic corrosion is to isolate the two metals from one another. This can be achieved by good design and where necessary by inserting an insulating material such as neoprene between the metal/metal contact.

Exfoliation Corrosion
Exfoliation corrosion is a specific type of selective attack that proceeds along multiple narrow paths e.g. grain boundaries which run parallel to the surface of a metal. Generation of corrosion products forces the layers apart and causes the metal to ‘swell’. Metal flakes may be pushed up and even peel from the metal surface. Exfoliation corrosion is most common in the heat treatable Al-Mg-Cu and Al-Zn-Mg-Cu alloys. This form of corrosion is associated with a marked directionality of the grain structure. Applied stresses are not necessary for exfoliation to occur. However, in alloys susceptible to stress corrosion cracking, the corrosion product wedging action undoubtedly contributes to the propagation of the exfoliation attack. It is important to note tht some alloys not susceptible to stress corrosion cracking (Al-Mg-Si) may suffer exfoliation corrosion. However, if the grain structure is equiaxed, exfoliation corrosion does not usually occur.
All I can say is that when aluminium contacts with oxygen is undergoes oxidation, which is harder than aluminium itself, and this is what protects it from corroding. Maybe from the exposure to heat the oxide layer is thicker than normal.???
It looks like the original roughness has filled up with sanding debris. Stuff like aluminum particles, aluminum oxide particles, and abrasive particles. Practically any kind of original surface should have been removed with a few hours of sanding.

Rubbing debris over debris will produce "glazed" surfaces filled with embedded, slick, fused particles.The sandpaper stops sanding and the surface you are trying to abrade will continue to accumulate debris.

When you see any spots on the paper that don't move, you are headed for glazing problems.

Leaving traces of heat goo on the aluminum is also asking for glazing problems. I know from experience. Clean it good before you start.

You could try filing it to get you back to square one. Having files fill with particles is also a problem. Wire brush them out at the first sign of sticking or you will never get them out.
mine has done that too, but i havent looked at it close up, it only happened after lapping, the reason it happens with this is because it is and aluminum alloy and not pure