Co-extrusion of Dual Aluminum Alloys with Special Surface Properties

Co-extrusion method is used for production of a dual Aluminum rod. The surface layer material for co-extrusion is prepared by rapid solidification process. The alloys Al-4.5Mg-1.0Ag (wt%) and Al-4.5Mg are selected as the surface and the bulk materials, respectively, and are co-extruded at high temperature range (450-480°C). The microstructures of rapid solidified Al in co-extruded rod consist of small grains (50µm) and some small particles (0.1-1µm). A proper annealing on the extruded rod increases the surface hardness more than 30%. Since the co-extruded material contains small T-phase particles, this increase in hardness indicates precipitation of a metastable Mg-Ag phase or a Mg-Ag-Al phase at 160°C during annealing.