Effects on hardening and ductility of severe plastic deformation of Al-Cu-Li and Cu-Cr-Zr precipitation hardening alloys

Abstract

Severe plastic deformation of precipitation hardening alloys offers the possibility of processing the solutionised material at room or high temperature, with ageing before or after deformation. Different strengths and ductilities arise because of complex interactions between precipitates and dislocations. Such interactions have been examined by ECAP of two precipitation hardening alloys. ECAP of Al-Cu-Li at room temperature leads to moderate strength with poor ductility, with subsequent ageing improving both. ECAP at elevated temperatures gives good strength with moderate-to-good ductility, depending on processing conditions. Detailed microstructural analysis shows that precipitates play a major role in determining both strength and ductility. ECAP of solutionised and/or aged Cr-Cr-Zr leads to hardening but low ductility, while subsequent ageing increases substantially both strength and ductility. The role of ECAP temperature is complicated, determining the microstructural state. The balance of substructural refinement and dislocation and precipitate hardening is analysed here to explain the mechanical properties.