I am doing project of improve the fatigue strength of Al 6063 T6 by precipitation hardening
As reported in ASM Metal Handbook, this easily extrudable alloy nominally contains 1.1% Mg2Si. Its solution heat-treating temperature of just over 500 °C (930 °F) and its low quench sensitivity are such that this alloy does not need a separate solution treatment after extrusion but may be air quenched at the press and artificially aged to achieve moderate strength, good ductility, and excellent corrosion resistance.
Solutionizing is normally carried out by heating the Al 6000 series alloys to around 550oC, providing a dwell time for conversion of the RT structure to a single phase solid solution and then quenching using a suitable media so that a super saturated solid solution is obtained. Then aging treatment is given.
Deionised water is used as a popular quenchant which can be used for your work.
I personally disagree with the lengthy solution temperatures and ageing temperatures. As explained in my 'Complete Casting Handbook 2015' and elsewhere, it is sensible these days to use the formula of 10 C rise in temperature is equivalent to a doubling of the rate of reaction. Thus a solution treatment at 530 C for 12 hours is equivalent to 540 C for 6 hours or 550 C for 3 hours
If the iron content is sufficiently low it might be possible to go to 560 C for 1.5 hour. I tend not to use treatments shorter than I hour because of the uncertainties added by the heat up and cooling times which start to become significant.
Similarly for ageing treatments, the commonly used 175 for 8 hours is equivalent to 185 for 4 hours, or 195 C for 2 hours. In general I tend to use the easy-to-remember 200 C for 1 hour for Al-Si-Mg alloys, which is usually sufficiently good.
Non of these recommendations delivers quite as good properties as the lengthy treatments, but the loss is negligible in view of the huge energy savings. In addition, if the alloy has been cast well, without the normal dense population of oxide bifilm cracks (again see CCHB), the generous elongation which will be automatically achieved avoids the extreme loss of ductility which is normal with these peak strengthening treatments, and which in general causes the peak treatments to be avoided in favour of under-aged treatments. For well cast material relatively free from defects the under-aged treatment is no longer a necessary precaution.
Aging at 200oC for 1 hour is certainly a faster approach to achieve peak aging, but it may lead to lower endurance of this peak aged alloy (owing to lower tensile elongation as compared to longer aging treatments and hence lesser enclosed area under the Load-displacement curve).
Thus, the fatigue characteristics may get affected when the higher temperature aging is employed.
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