Influence of Grain Size on the Portevin-LeChatelier Effect in Al–Mg Alloys

Abstract

In order to investigate the effect of grain size on Portevin-LeChatelier yielding, tensile tests were performed on Al–0.55 and 1 at% Mg alloys having various grain sizes. In a temperature range of −20°∼+40°C and a strain rate range of 3.3×10⁻⁵∼1.7×10⁻³/sec, the value of activation energy for the P–L effect was found to be 0.60±0.02 eV independent of grain size. The relation between strain rate \dotε and strain ε₀ required for the onset of the P–L effect at 0°C was expressed as \dotε∝ε^2.0±0.1 μ^0.53±0.02 where μ is grain size. It was found that the value of ε₀ was decreased and the stress at the onset of the P–L effect was increased with the decrease of grain size. The above fact is explained by the effect of grain size on the average velocity of moving dislocations.