| The present study aims at investigating the effect of SiC particulates size and heat-treatment on the tensile properties of SiC_P/AZ91 Mg composites. The AZ91 Mg alloy powders were made by wet attrition milling from AZ91 Mg machined chips and the powders size was below 240㎛. The SiC particulates size used as a reinforcement was 8, 30 and 50㎛, respectively. The Mg powders and SiC particulates (10 vol%) were mixed using a V-blender for 2 hours. Both AZ91 Mg alloy powders and mixtures of AZ91 Mg alloy powders and SiC particulates were hot pressed at 400℃ to make round billets. The billets were hot extruded at extrusion temperature of 300℃ under extrusion ratio of 40:1. The extruded Mg matrix and SiC_P/AZ91 Mg composites were solution treated at 410℃ for 17 hours, quenched into ice water, and then aged at 170℃ for 40 hours. It was found that the ultimate tensile strength of as-extruded composites is much higher than that of the as-extruded Mg matrix. As SiC particulates size decreased, the U.T.S. of as-extruded composites tended to increase. This could be attributed to the matrix grain refinment caused by the present of SiC particulates and the reduction of crack formation by the fracture of SiC particulates during hot extrusion. After T_6 heat treatment, the U.T.S. of heat-treated composites was found to be superior to that of as-extruded composites. Also, the U.T.S. of the composites was considerably increased with decreasing particulates size after T_6 heat-treatment. The reason for this is the restriction of the matrix grain-coarsening by fine SiC particulates during solution treatment. |
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