The effect of Fe, Mn and Sr on the microstructure and tensile properties of A356-10% SiC composite

This study investigates the formation of Fe containing intermetallic compounds on the microstructure and tensile properties of A356-10% SiC composite in the Mn- and Sr-modified conditions. The composite ingots were made by stir casting process and iron was added to the remelted composites at different concentrations varied from 0.5 to 2%. For 2 wt.% Fe, different levels of Mn were added to identify the optimum Mn:Fe ratio for eliminating harmful beta-phase and obtaining microstructure with well distributed and fine intermetallics. 300 ppm Sr was added to the Mn-modified composite to investigate the effect of Sr and Mn on the microstructure and tensile properties of A356-10% SiC. T6 heat treatment was applied for all specimens. It was found that the addition of Mn changes the morphology of Fe-rich intermetallics from plate-like beta- to alpha-phase. The tensile test results demonstrated that the addition of iron considerably reduces both UTS and elongation values while, modification by Mn and Sr improves tensile properties of the composite with 1 and 2 wt.% Fe. Fractographic examination of iron containing composites also showed that large beta-Fe intermetallics are responsible for fracture behavior in unmodified condition. (C) 2010 Elsevier B.V. All rights reserved.