Influence of heat-treatment and solute content on repeated precipitation at dislocations in Al-Cu alloys

Abstract

The influence of heat-treating parameters and Cu content on repeated precipitation of theθ′ phase which occurs at climbing dislocations during quenching dilute Al-Cu alloys has been studied by transmission electron microscopy. In Al-3.85 wt % Cu the process occurs during quenching from all temperatures within the solid solution range to all temperatures in the range from room temperature to at least 300° C. It also occurs over a wide range of quench rates. Depending on the quench rate, it can occur at a variety of dislocation geometries, including climb sources, glide dislocations which climb off their slip planes, and collapsed vacancy loops. Quenching directly to the ageing temperature establishes the distribution of almost the entire volume fraction ofθ′ by repeated precipitation during the quench. This process does not occur in alloys with Cu content below 1.5 ± 0.5 wt %.