Effect of grain size and dislocation density on thermal stability of Al-Cu-Mg alloy

Thermostable Al alloys have been a consistent focus for decades, mainly adopting alloying strategy to improve thermostability of precipitates. In this work, it was found that matrix defects controlling could be a new way to improve thermal stability of Al alloys. Three alloys with composition of Al-4.1Cu-2.1Mg-0.3Mn but varied dislocation densities and grain sizes were prepared, and their thermal stability at 200 °C were investigated by identifying hardness vs. holding time curves. It revealed that the alloy with high dislocation density and small grain size showed poor thermal stability. Because dislocation and grain boundary provided accelerated diffusion channels for Cu and Mg atoms, leading to rapid growth of S’(Al₂CuMg) precipitates, and the growth rate was a liner function of square of dislocation density ρ² or square of grain size reciprocal 1/d² according to data fitting. A “dislocation affected zone” model was proposed to explain the diffusion phenomenon.