EFFECT OF PRECIPITATION HARDENING ON STRAIN RATE SENSITIVITY AND YIELD BEHAVIOR IN AN AL-MG-SI ALLOY

The effects of precipitation hardening on the strain rate sensitivity of the flow stress and the yield behaviour in an Al-Mg-Si alloy have been investigated. In samples aged for less than 4 h at 160°C measurements of Δσ Δlnε{lunate} were found to decrease with increasing strain, becoming negative at a strain which increased with increasing ageing time. For longer ageing times Δσ Δlnε{lunate} remained positive at all strains. Serrated yielding was found to occur in samples where Δσ Δlnε{lunate} < 0. The results are discussed in terms of recent models for dynamic strain ageing based on the diffusion of solute atoms to temporarily arrested dislocations. © 1979.