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6061-T6 machined surface defects - moon craters

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DWilliamA

Materials
Oct 11, 2010
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This is a continuation of thread (now closed) thread281-283298

my ultimate question.... unless someone has a machining related solution... will heat treat help this? working with 6061 T6 Bar stock 3/4"x3"

During the last runs 6 months age we had copper contaminated coolant, since then we have replaced our coolant and run no copper. we have machined up batches that come out perfect since then too. This last batch is terrible.

This pieces are machined down .100" for the top surface (Photo 1)with the big individual white spots, (note there are some starter holes in the photo too) next level down .125" for the second surface (photo 2) which shows the 'galvanized' or 'moon crater' type surface which is a little stronger along the edge of the part and hard to see, and a 3rd surface about 3/8" down which is clean (no photo).....

this indicates a material issue? the raised white spots are raised, you can see that the obrounds are actually raised via shadow castings, not sunken or crater like. you have to look real close to see these, get them in the light just right... most people don'e even notice them at first glance.

This part gets hard type III anodized and these defect show right through and look bad.

machining technique... heat treat and clean the grain up?
 
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