Non-destructive characterisation of microstructure evolution in Mg based metal matrix composites submitted to thermal cycling

Acoustic emission (AE), damping and dilatometry techniques have been developed to study microstructural changes due to thermal stresses in commercially pure Mg-alumina metal matrix composites submitted to thermal cycling. AE shows that the thermal stresses are accommodated by dislocation generation and motion in certain temperature ranges whose fashion is dependent on the upper temperature of cycling and the amount of reinforcement. An increment in dislocation density connected with a redistribution of solute atoms on dislocation lines is revealed after the thermal cycling by damping measurements. The thermal stresses are also characterised by the residual deformation measurements carried out by the dilatometry. For a constant upper temperature of cycling the microstructure does not develop distinctly with increasing number of cycles.