Problem- Bad Lot of Aluminum?

[NID]

I regularly turn out parts on my CNC from 5 1/2" diameter aluminum, 6061 T6511. Today the parts from a new batch of this stock would not make a good finish -looks a bit like chatter marks but its not. After trying everything to make sure it was not tooling, inserts, speeds, feeds, -I finally ran some older material and no problems! I am forced to conclude it is a bad batch of alum. The spec sheets are very similar to everything else I have ever run over the past 10 years except that the elongation numbers (tensile strength?) are higher.

Has anyone ever had a problem like this??
Thanks,
Jeff

[martinw]

Dear Jeff,

My guess is that you were sent the wrong spec. stuff by the people you buy your Al from. It was probably put in the wrong rack at their end, and you got sent it. It will be hard to prove it to them though...

Anyway, good luck,

Best wishes,

Martin

[Geof]

With 'bad' aluminum my first suspicion is wrong temper. What was the chip formation like; similar to old stuff or are the chips stringier? It is not easy to tell if you are milling it but drilling holes or turning low temper aluminum can make long stringy chips. The higher elongation number suggests lower temper material that is more ductile.

Have you got back to your supplier to find out if this is sourced from the same mill as your earlier orders.

[martinw]

Occam's Razor?

The simplest answer is probably the most likely.

1) Did the aluminium smelter people screw up the ingredients when they brewed up a few hundred tons of the stuff? Possible, but unlikely. They probably have metallurgist's reports to complete for the aerospace boys, and are unlikely to falsify it.

2) The people that Jeff bought his stock from simply sent him the wrong spec stuff. That could happen either by a clerical error, or something as simple as the wrong stock being stored, as it was put on the storage rack late on a Friday, by a guy who was keen to get away in a hurry.

Option 2 seems to be a good one.

Best wishes,

Martin

[NID]

Thank you for your input. I wanted to follow up on how this was resolved. I ended up returning the bad alum. and getting another piece from a different lot. Started machining it today and it made all the difference. Even though the mill specs were very similar. All I know is there was something really weird about that other material.
Thanks again,
Jeff

[Nastyzen]

I had a similar problem a while back.The material was to be T-6 but in fact was much softer.The instant the cutter touched the 2'' dia by 8''long blank it galled and came out the chuck at 2000rpm taking out the tool in the process and when I received the mill specs from my supplier,it turned out to have come from china!To top it all off the spec sheet had been filled out by hand in Chinese...
Now when I order I specify no Chinese materials and proper paper work please.