| Aluminum alloys, such as A356, are widely used by aerospace and automotive industries to reduce weight, increase production, reduce cost, and prevent corrosion of components. Since these components are in high temperature environments, creep behavior is an important design parameter. Understanding A356 at high temperatures provides important information for using the alloy as matrix materials in composites. Casting plaster was the primary mold material in casting A356 with graphite mold material introduced for a comparative study. The plaster has about half the thermal conductivity and one-third the heat diffusivity of sand, making plaster an unusual mold material. Plaster molds provide repeatable results, fine detail and reasonable strength. The experimental heat treatment giving properties most closely resembling T6 for sand castings of A356 gave the values of tensile and yield strengths of 210 MPa and 168 MPa, respectively. The mechanical limits for sand casting alloys for T6 temper of A356 was referenced at tensile and yield strength of 234 and 165 MPa, respectively. Therefore, the yield strength was less than the limit for sand casting, but the yield strength was within the specification. The mechanical properties ranked from highest to lowest, permanent mold > sand mold > insulated mold suggesting that plaster molds act as insulators rather than conductors. Elevated temperature tensile experiments of aluminum alloy A356-T6 was performed at constant load and 0.73, 0.78, 0.87, and 0.92Tm. An Arrhenius rate equation was explored to characterize the behavior for a pair of temperatures via steady state strain rates and activation energies. Overall, the consistency of the tensile specimens suggests plaster casting will work well for future A356 composite tensile specimens and creep behavior of plaster cast specimens. |
