Effect of extrusion temperature on microstructural evolution and intergranule bonding of Al-7Si-0.3Mg (wt%) alloy rods produced by extrusion of granule compacts

Al-7Si-0.3Mg (wt%) alloy rods were produced by extrusion of granule compacts at temperatures of 400, 450 and 500 °C, respectively. The granules were produced by grinding recycled Al-7Si-0.3Mg machining chips. Fracture and redistribution of Si and Al3FeSi particles along the extrusion direction occurred during extrusion, leading to excellent ductility of the consolidated samples with an elongation to fracture ranging from 16.6 to 20.5%, being much higher than that of the Al-7Si-0.3Mg casting alloy. The Al-7Si-0.3Mg alloy rods showed a bimodal size distribution of α-Al grains as a result of recrystallization and growth of new grains. With increasing extrusion temperature from 400 to 500 °C, the mean grain size of the α-Al matrix increased from 5.6 to 7.8 μm. Meanwhile, rapid establishment of good intergranule bonding was achieved in the Al-7Si-0.3Mg alloy rods during extrusion due to effective breaking of oxide layers on the granules and fast atomic diffusion bonding between the atomically fresh surfaces of the granules.