Mechanical Property Enhancement Due to Plastic Deformation Prior to Peak-Age Hardening in an Al-Mg-Si Aluminium Alloy

Abstract

The effect of plastic deformation prior to peak age-hardening on mechanical properties of an Al-Mg-Si-Cu aluminium alloy was investigated. The alloy was prepared by DC casting and then hot extruded into flat strips of 3 mm in thickness, which were immediately quenched after extrusion to obtain a supersaturated solid solution state. The extruded and quenched flat strips were either left naturally-aging for a controlled short period of time or pre-aged before deformation. Plastic deformation was performed at room temperature by cold rolling or stretching to a strain of 4% or 8%. Hardness measurements and tensile testing were performed to obtain the mechanical properties of the alloy under different processing conditions. Scanning electron microscopy techniques, including electron backscattered diffraction (EBSD), were conducted to characterize microstructural features such as the dislocation density and crystallographic texture. Experimental results showed that the combination of pre-ageing and deformation by stretching resulted in a significant increase in the mechanical properties after the final peak ageing treatment. The interactions between dislocations and pre-ageing induced solute clusters and fine precipitates during deformation are considered to have increased the dislocation density in the material and promoted heterogeneous nucleation during final age hardening treatment.