Abstract
A remarkable solution softening phenomenon was found in the tensile test of Al–Mg–Zn alloys at high temperatures. The effect of zinc addition was studied and the softening mechanism is discussed. The results are summarized as follows:
(1) The flow stress level of Al-3.3 at%Mg alloy decreased linearly with increase in zinc concentration. The decreasing rate was about 4% per 1 at% of zinc.
(2) The high temperature deformation behaviors of Al–Mg alloys was not changed essentially by the addition of zinc. For both binary and ternary alloys, the following mechanical equation of states is given:
\dotε=Aσnexp(−Q⁄RT),
where \dotε is the strain rate, σ the applied stress, A a constant depending on the concentration of zinc, n=3.3, Q=36∼37 kcal/mol and RT has its usual meaning.
(3) The high temperature deformation of Al–Mg–Zn alloys as well as that of Al–Mg alloy is governed by the viscous motion of dislocations which drag magnesium atmospheres formed around them. The solution softening observed can be attributed to the enhanced diffusivity of magnesium which is caused by the addition of zinc.
