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I've been looking at using Aluminium 6082-T6 structures in impact energy absorption mechanisms. I planned to do some material testing, made specimens for testing then was distracted with another project for about a year. When I finally tested these specimens they broke in a surprisingly brittle manner with a much higher than expected proof stress.

I'm wondering whether 6082-T6 is an alloy that age hardens at room temperature as one of the technicians suggested this as the cause. If so, does anyone know of any studies into this phenomenon?

This is would be rather important for impact energy absorption as increasing proof stress can result in higher risk of fatality.

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Just leaving the alloy sitting on a shelf for a year at room temperature shouldn't have any effect on it.

However, 6082-T6 "as supplied" has already been heat treated and artificially aged. That's what the -T6 temper designation means.

If you wanted "soft" ductile material for energy absorption, maybe you should have used 6082-O (or some other temper designation) instead of -T6.

Another possibility is that the manufacturing operations to make your test specimens affected the state of the material, and the finished specimens should have been heat treated again.

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  • $\begingroup$ Thank you, I'll have to do some further testing and look at 6082-O as well. $\endgroup$ – Era Dec 17 '16 at 13:50
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That alloy/temper should be stable when it leaves the manufacturer. I have a piece of 6061 T6 that I've been hardness testing (Rockwell) over the last 10 years, I don't believe the hardness has ever changed; if it has, it wasn't enough to affect its performance.

You didn't say if you had tensile tested them before you got distracted. It may be that the extruder or heat-treater, left them in the age oven too long. Depending on the temperature they were running, they could've blown the grains, the result would be brittle material. If you have the means, do grain size analysis. Our 6082 is usually between a 4-6 ASTM. If it's brittle, the grain size might be down below 3 ASTM. We had a customer leave a part in a braze furnace too long, and then complained our tube leaked. The grain size was measured at a -2 ASTM :-O Sorry, not our fault.

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