Experimental study of the interaction of magnesium with the reinforcement in AlMgSi alloy/α-alumina platelet composites

The age hardening capacity of composite materials is closely related to their processing history. Chemical interactions may take place between the alloying elements and the reinforcement, leading to reduced structural hardening of the matrix. The aim of this study was to identify the mechanisms of interaction implied in the solutionizing treatment of AlMgSi alloys reinforced with a continuous network of α-alumina platelets. Thermoelectric power measurements, electron microprobe analyses and transmission electron microscopy investigations clearly demonstrated a decrease in the magnesium content of the solid solution of the matrix during the solutionizing treatment. This is the result of competition between two mechanisms. Magnesium can diffuse through the entire mass of the material and preferentially along the continuous network of interfaces created by the interconnected platelets, before leaving the composite towards the external surface of the composite. It can also react to form MgAl2O4 spinel at the interface.