Unlike steel, which normally will not become permanently stressed at load levels significantly below the threshold where some stretching begins to show up, even with many, many repetitions of the stress, aluminum has no such threshold, and can become fatigued by such repeated stress, even at levels lower than the point where permanent deformation would have occurred in virgin material.
Some common aluminum alloys, such as 6061 are more prone to this situation than say ... 7075, but the issue needs to be taken into account if many (thousands) of cycles that might approach the listed tensile limits are anticipated.
The T6 spec is a heat treat condition that gives much more strength due to an artificial aging effect. Part of this treatment is a soak at the quite low temp of around 325 degrees. I'm not expert at this, but suspect exposure to much higher temps might negatively affect the heat treat rating.
Not to say don't use aluminum, but just to say do the research and testing first.
This message has been edited by lhd from IP address 220.127.116.11 on Dec 1, 2011 11:50 AM
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