6061-T6

[Peru]

We use 6061-T6 in lasers, and prior to using them we bake them at 250°C for 12-14 hours and allow to air cool? Does this have any effect on the material? Hardness, temper? None of the material I researched indicates a change to the material properties?

Thanks

 

[metengr]

Yes, and here is the reason. The heat treatment for AA 6061 T6 is as follows;

Solution treatment 960- 1075 deg F
quench in water
Artificial Age (Precipitation heat treatment)
@ 350 deg F for 8 hours

This information was obtained from ASTM B597 -Standard Practice for Heat Treatment of Aluminum Alloys. This would apply to various shapes; extruded tube, rod, structural shapes....

The reason I provided the background information on 6061 T6 was to show that the solution treated/artificially aged aluminum alloy will loose strength upon exposure to any subsequent temperatures above 350 deg F. At 250 deg C (482 deg F) you are well above the precipitation heat treatment temperature and, as such, would soften the T6 material to a different temper/strength upon exposure for 12 hours at temperature.

For additional information, the MIL-HDBK-5H has a section on Aluminum alloys, and more specifically mentions exposure of heat treated aluminum alloys to elevated temperatures (3.1.2.1.8) that can degrade strength over time.

The reason for the decrease in strength and hardness is because of exposure to temperatures above 350 deg F (the artificial aging temperature), which causes the precipitates from artificial aging to coarsen over time at temperature. The plus side to carbide coarsening is increased ductility and toughness for the alloy.

 

[EdStainless]

Will these parts get hot in service? It may be done to prevent the overaging from happening over the course of service. By forcing it before you assemble you can make sure that dimensions and line-up are correct. And they will be more likely to stay that way.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[Peru]

Thanks for the info...so not only do the material specs change with temp but apparently dimensions as well...up to .0015 in/in. I am now curious about the dimensional/spec stability of non-heat-treatable AL alloys e.g. 5052-H32 at the elevated temps. Any ideas on this?

 

[metengr]

The 5052 aluminium alloy in the H32 temper implies the following;
- Strain hardened and stabilized to a quarter hard condition.

This applies to products that are strain-hardened from cold working and whose mechanical properties are stabilized, either by a low temperature thermal treatment or as a result of heat introduced during fabrication. Stabilization usually improves ductility".

At your bake temperature of 250 deg C (482 deg F), you will most likely remove the benefits from cold working, and reduce the strength from a 1/4 hard condition. I would also expect some affect on dimensional stability for the H32 temper during exposure to the 250 deg C bake for 12 hours.

Why not use the same aluminum alloy (5052) in the fully annealed condition - O temper ? The annealed condition would improve dimensional stability for this 12 hour bake at 250 deg C? Do you need the increased strength for your application?

 

[Peru]

In my application, dimensional stability is more critical than strength (machined tolerances of +/- .001 over 12"), so I'm curious to see if the 5052-0 will maintain that before and after baking.