Microstructures and tensile mechanical properties of an ultrafine grained AA6063–5vol%SiC metal matrix nanocomposite synthesized by powder metallurgy

A bulk ultrafine grained (UFG) AA6063–5vol%SiC metal matrix nanocomposite has been synthesized by consolidation of a nanocrystalline AA6063–5vol%SiC nanocomposite powder using two powder metallurgy (PM) routes: one combining spark plasma sintering (SPS) and hot extrusion and the other combining die pressing and hot extrusion. The yield strength, ultimate tensile strength and elongation to fracture of the sample produced by a combination of SPS and hot extrusion at 500°C are 392MPa, 496MPa and 7.1%, respectively, while those of the sample produced by die pressing and hot extrusion are 449MPa, 526MPa and 3.5%, respectively. Pre-sintering of the powder compact using SPS prior to extrusion improves the ductility of the consolidated material without causing significant decrease of strength, suggesting that SPS has a beneficial effect on improving the consolidation level of the material. The UFG microstructure of the AA6063 matrix is the result of recrystallization of the as-milled nanocrystalline AA6063–5vol%SiC nanocomposite powder particles during extrusion. With increasing the extrusion temperature from 500 to 550°C, the average grain size of the consolidated sample increases from 276nm to 627nm, leading to a significant decrease of the yield strength from 449 to 233MPa, but a drastic increase of the elongation to fracture from 3.5% to 9.6%.