7075-O Natural Aging Time @ Room Temp

[spencbrins]

I can't find any information on the natural aging time of 7075-O aluminum. I've checked the AMS book "Aluminum and Aluminum Alloys" and they dance around the question:

"Most of the heat treatable alloys exhibit age hardening at room temperature after quenching. The rate and extent of such hardening varies from one alloy to another. Microstructural changes accompanying room temperature aging, except for long-time aging of 7XXX alloys, are undetectable because the hardening effect are attributable solely to the formation of zone structure within the solid solution."

"Alloy 7075 and other 7XXX series alloys continue to age harden indefinitely at room temperature; because of this instability, they are very seldom used in the W temper."

I've only been able to find information on tempered 7075.

Does anyone know how fast annealed 7075-O naturally age hardens at Room Temp?? (if at all?)

http://files.engineering.com/getfil...b3bb961bf2&file=Aging_at_room_temperature.JPG

http://files.engineering.com/getfil...cteristics_of_aluminum_sheet_alloys_at_RT.JPG

 

[swall]

You age from the solution treated condition. If you have annealed material (condition O), there will be no ageing.

 

[spencbrins]

Thank you Swall.

Do you by chance know if any mechanical properties change at all in 7075-O or is it completely stable in that condition?

Why is solution treated 7075-W use more often than 7075-O? O condition would be more ductile and easier to form am I correct?

 

[TVP]

As swall mentioned, the mechanical properties essentially do not change (they are stable) for 7075 in the O temper (annealed). I'm not sure that I would say that -W is used more often than -O, but one reason to use age hardening alloys like 7075 in the solution treated condition is to perform cold working operations like drawing, extrusion, etc. so that the subsequent aging process will produce maximum strength. This process of solution treat (and quench) + cold work + artificial aging is called the T9 temper, and usually improves ultimate tensile strength by about 20-100 MPa vs. T6 temper. And yes, the annealed temper has maximum formability, but the difference between -O and -W is not all that great as long as the forming is done within several hours of the solution treating operation.