Effect of heat treatment on the strain hardening behaviour of an Al-Zn-Mg alloy

Artikel i vetenskaplig tidskrift, 2009

The strain hardening of the Al-5.2Zn-1.2Mg alloy AA7030 in different conditions has been investigated. The dislocation related strengthening was described by the Voce equation and the quantitative effects of different superposition laws have been studied. All tempers, except the over-aged, suffer from plastic instability before the geometric Considère condition is reached. This was attributed primarily to the occurrence of shear failure due to dynamic strain ageing effects. For plastic strain levels below approximately 8 %, preceding the plastic instability, the results show that the saturation stress in the under and peak-aged tempers is independent of heat treatment, whereas the kinetics of structure formation differs. Using a linear superposition law in the under and peak aged tempers has negligible effects, whereas the use of Pythagorean addition for the over-aged temper significantly decreases the goodness-of-fit, although not to unacceptable levels. Furthermore, the naturally aged temper shows strong influence of dynamic precipitation.