Aluminum Tempers 6061 T651 vs 6511

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Have my new SO5 cutting through some aluminum, good clip about 2000mm/min, 1.5 DOC, 20k RPM with a fogbuster (mainly for some deep slotting). Using an Amana .25" single flute Zrn coated cutter.

However, I have noticed some surprising differences in raw material. Locally, I use Caremark Metals for aluminum stock, usually an extruded 60601 T6511 bar that is chopped off at whatever lengths I need. (usually 6x12x1"). This seems to cut very very well. I dare say like butter.

However, they are a bit more expensive than what I find on Amazon, and Amazon ships to my door, so I got some of these.

It is surprising how different the Amazon stuff is to cut. Lots more coolant, have to go slower, not as clean of a cut. From what I read, the tempers are pretty much identical T651 vs T6511, and the extra “1” is to imply it was straightened.

Sometimes I think I am crazy, but I wouldn’t have expected this much of a difference.

Just looking for thoughts on the matter, or what temper is best for machining?

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I’m no metallurgist but I think T6511 is extruded only and has less internal stress than T651 which has less than T6, due to it having an additional step of stress relieving. Since T6511 has fewer internal stresses it technically is better for machining since it doesn’t move as much as T651 when machined. Alloy wise they should both have the same composition of metals, maybe the difference in machining quality is caused by the quality of the aluminum sold by the seller?

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Makes sense. Hard to know the quality of the metal when buying from Amazon. But, I placed another order with my normal supplier which is a known good.

Thank you!

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