Influence of Si and Ge Microalloying Additions and Plastic Deformation on Precipitation Processes in Al-Cu Based Alloys

Abstract

The combined effect of micro-alloying with Si and Ge and/or plastic deformation prior to ageing at 160°C on age hardening has been studied in an Al-2 at% Cu alloy. The results obtained indicate that the hardness response is faster and the peak hardness is higher when plastic deformation and micro-alloying are applied together than performing each procedure individually. Different amounts of deformation, ranging from 0% to 30% have been utilized. An optimum deformation degree for the hardening response has been established around 8% for the Al-Cu-Si-Ge alloy. Characterization by transmission electron microscopy (TEM) shows that the peak hardness is due to a complex microstructure that contained θ" disc shaped precipitates, rod-shaped Si-Ge precipitates and θ' plates that were heterogeneously nucleated on the Si-Ge particles. Pre-deformation has been found to stimulate the growth of the θ' plates due to enhanced diffusion along dislocation cores. Increasing deformation reduces the influence of the Si-Ge precipitates on heterogeneous nucleation, leading to reduced peak hardness and faster over-ageing.