EXPERIMENTAL-STUDY OF THE INTERACTION OF MAGNESIUM WITH THE REINFORCEMENT IN AL-MG-SI ALLOY ALPHA-ALUMINA PLATELET COMPOSITES

The age hardening capacity of composite materials is closely related t o their processing history. Chemical interactions may take place betwe en the alloying elements and the reinforcement, leading to reduced str uctural 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 alpha-alumi na platelets. Thermoelectric power measurements, electron microprobe a nalyses and transmission electron microscopy investigations clearly de monstrated a decrease in the magnesium content of the solid solution o f 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 n etwork of interfaces created by the interconnected platelets, before l eaving the composite towards the external surface of the composite. It can also react to form MgAl2O4 inel at the interface.