Temperature and strain rate dependence of the dynamic strain aging effect in an Al-Zn-Mg alloy

An AA7030 alloy (Al-5.4Zn-1.2Mg) was tested for evidence of dynamic strain aging in naturally aged and peak aged condition and under varying conditions in terms of strain rate and temperature. Clear evidence in terms of strain rate sensitivity, serrated yielding (Portevin-Le Chatelier effect) and propagative plastic instabilities was observed in the naturally aged temper while the peak aged temper only showed serrated yielding. Further evidence of dynamic strain aging was the temperature and strain dependence of the strain rate sensitivity, which can be explained by the additional dislocation activation energy resulting from solute pinning. Investigation of the specimen surfaces was carried out to reveal an orange peel structure with pronounced glide bands. Small cracks within individual grains rather than grain boundary cracking could be observed.