Temperature and strain rate dependence of the dynamic strain aging effect in an Al–Zn–Mg alloy M. Ho ¨rnqvist and B. Karlsson* 1 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. Keywords: Al–Zn–Mg alloy, Dynamic strain aging, Portevin–Le Chatelier effect, Tensile tests, Temperature effects, Strain rate effects List of symbols b magnitude of Burgers vector C solute concentration at dislocation C 0 average solute concentration C S saturation concentration at dislocation D diffusion coefficient k B Boltzmann’s constant K diffusion process dependent parameter l average obstacle spacing R p0 . 2 0.2% offset yield strength S strain rate sensitivity t a aging time t f flight time t w waiting time T temperature V activation volume Dg additional activation energy from DSA DG 0 thermal activation energy e (plastic) strain : e (plastic) strain rate n attack frequency V elementary strain increment r m mobile dislocation density s* effective stress S 5 Ls L ln : e S 0 e 5 LS Le ~ L Le Ls L ln : e   S 0 T 5 LS LT ~ L LT Ls L ln : e   Dg 0 5 LDg L ln : e Dg 00 e 5 LDg 0 Le ~ L Le LDg L ln : e   Dg 00 T 5 LDg 0 LT ~ L LT LDg L ln : e   C 0 5 LC L : e C 00 e 5 LC 0 Le ~ L Le LC L : e   C 00 T 5 LC 0 LT ~ L LT LC L : e   Introduction Dynamic strain aging (DSA) is a commonly occurring phenomenon in alloys, where mobile solute atoms interacting with moving dislocations can cause some unwanted yield phenomena. The first model set up by Cottrell and Bilby 1 assumed a continuous dislocation motion and required solute atoms with enough mobility to follow the moving dislocations through the lattice. It was later realised that the mobility of the solute atoms was too low to allow for this condition, and instead a model based on a discontinuous dislocation motion was proposed by McCormick 2 which showed better agree- ment with experimental results. The dislocation motion is assumed to be divided into two distinct steps: during the waiting time t w , the dislocation is held up at Department of Materials and Manufacturing Technology, Chalmers University of Technology, SE–412 96 Go ¨ teborg, Sweden *Corresponding author, email birger.karlsson@chalmers.se ß 2006 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 6 June 2005; accepted 1 January 2005 DOI 10.1179/174328406X74284 Materials Science and Technology 2006 VOL 22 NO 2 213