Effects of processing on the properties of aluminum and magnesium matrix composites

A356 aluminum and AZ91 magnesium alloys were reinforced with SiC{dollar}sb{lcub}rm p{rcub}{dollar} and cast prior to hot deformation processing. Tensile properties and microstructural features were quantified for the composites heat treated to a T6 condition for each of the processing conditions. The aluminum composite material was supplied by the Dural Composites Corporation in ingot form with a 20 vol.% reinforcement level. The magnesium composites were processed at a 20 vol.% level with subliquidus stir mixing prior to casting. The molten composites were squeeze cast under 140 MPa of pressure. Additionally, the aluminum composite was sand cast and the magnesium composite was both sand and permanent mold cast. The A356 composite was hot worked via swaging to reductions of 33 to 95%; the AZ91 composite was hot extruded at a 92% reduction. The unreinforced alloys of these matrices were similarly processed and examined.; The combination of squeeze casting and hot deformation with 95% reduction for the aluminum composite and 92% reduction for the magnesium composite significantly improved the ductility. This improvement was accompanied by an increase in tensile strength of the aluminum alloy and in both the tensile and yield strength for the magnesium alloy. The best properties obtained were as follows for the A356-T6 composite: 279 MPa yield strength, 339 MPa tensile strength and 8.1% tensile elongation; and for the AZ91D-T6 composite: 310 MPa yield strength, 432 MPa tensile strength and 3.5% elongation attained. The particulate composite demonstrated an improvement in the modulus of elasticity. The A356 exhibited an increase from 65 to 100 GPa; while the AZ91D was increased from 42 to 70 GPa. Lower ductility resulted from the presence of the SiC{dollar}sb{lcub}rm p{rcub}{dollar} but the final ductilities exceeded those of published results.; These composites offer good properties as space structural materials with improvements over the unreinforced alloy. Improvements in specific stiffness were realized with the addition of 20 vol.% SiC{dollar}sb{lcub}rm p{rcub}{dollar}. The coefficient of thermal expansion was decreased for the AZ91D alloy by the presence of the SiC{dollar}sb{lcub}rm p{rcub}{dollar} in the composite. Exposure of these materials to a low earth orbit space environment did not produce any measurable degradation.