Influence of Heat Treatments on Microstructure and Mechanical Behaviour of Compressible Al Matrix, Low Density Composites

This work investigates the influence of solution/ageing treatments on mechanical properties under compression of a compressible, low-density composite based on AA7075 alloy as matrix, reinforced with porous ceramic particulates (foamed SiO2/Al2O3/Fe2O3). Composites were produced by thixoforming and products were characterized related to mechanical behaviour under semi-static compression, in different conditions: as thixoformed and after solution/ageing treatments. Structure of thixoformed material requires particular heat treatment conditions due to coarser secondary phases, when compared to as-cast situation. Products presented relative density around 0.5 and compression behaviour characteristic of cellular metals, showing plastic deformation plateau due to collapse of porosity, which gives the composites potential applications as energy absorbers. Effect of heat treatments upon the properties showed increase in the order of 2× of the maximum strength required to start plastic deformation and 5× in the average plateau strength, with only 15 % reduction of plastic deformation.