Natural Age Hardening of 6061 T6 3

[tc7]

We are using 6061 T6 for the manufacture of electronic equipment racks. Some of the detailed drawings call for a tight bend radius (R0.375) in .190 sheet stock. To accomplish this the shop wants to anneal the stock to 0 temper and then make all bends. I have been told that the stock will naturally age harden at room temperature back up to at least T4. Can anyone confirm this is true and suggest references.
Thanks in advance,
TC

 

[metengr]

tc7;
The attached file is from ALCOA and lists technical data on 6061, which should answer your question. From the information presented, this alloy must be solution treated after forming in the 0 temper (annealed) condition to obtain a T4 temper. Annealing the T6 material will not promote natural aging, after forming, to obtain a T4 temper.

http://www.alcoa.com/adip/catalog/pdf/Extruded_Alloy_6061.pdf

 

[TVP]

It will depend on the "annealing" parameters that are chosen. If a full solution treatment is performed (530 C and immediately water quenched) then natural aging will occur. However, if the part is only annealed to remove the effects of the T6 treatment, a typical process would be to soak at 415-440 C followed by slow cooling to ~ 260 C. This produces a microstructure with coarse, widely spaced precipitates, and hence low strength, due to the high diffusion rates allowing for maximum precipitate coalescence. If this process is performed, no natural aging will occur, and as metengr stated, the part will need to be solution heat treated after forming.

 

[metman]

tc7,
metengr and TVP are correct but you should also be aware of the following:

Instead of annealing (O condition), forming, solution treat and age, another option is to solution treat, keep the Aluminum refrigerated until formed, and allow to naturally age after forming. This is standard practice for much Aluminum alloy manufacturing.

While in the solution treated condition (W condition) the material is unstable and will naturally age harden if not kept refrigerated. While in the W condition the material is soft enough for most forming opertions although not quite as soft as in the O condition.

Jesus is THE life,
Leonard