The Behavior of Al-SiCp composites under thermal cycling conditions

n ABSTRACT Composites of an aluminium-silicon alloy (Al-7%Si-0.7%Mg) containing 10 and 20 vol. % particulate silicon carbide reinforcement and unreinforced matrix alloy samples were produced by the die casting technique. The cast ingots were extruded at 500 °C with an extrusion ratio of 10:1. Extrusion of these samples caused large- scale dynamic recrystallization resulting in a fine matrix microstructure. The extruded microstructures had a more uniform distribution of SiC particles in comparison to the as-cast microstructures. In the study, the tensile ductility and the potential of superplastic deformation of these materials were evaluated under high temperature tensile and thermal cycling conditions. The microstructures and mechanical properties of the matrix alloy and the composites were investigated. The high temperature tensile tests were carried out over the temperature range from 25 to 430 °C. Mechanical properties after extrusion show that the composite samples have strength values superior to that of the matrix alloy at ambient temperature. Elevated temperature results indicate that the composites exhibit good strength retention up to 300 °C and the effect of SiCp disappears as the temperature increases. The strain rate sensitivity exponent, m, was observed to be 0.11, 0.13 and 0.07 for the A1Sİ7 alloy and 10, 20 vol.% SiCp composites respectively at 430 °C and in the strain rate range from 4xl0"5 to 4x1 0"2 s"1. Thermal cycling tests were performed between 100 °C and 430 °C under a constant tensile load in a stress regime of 5-14 MPa and 3-5 MPa. The observed strain rate range was from 10"6 to 10"4 s"1. Under optimum loading and thermal cycling conditions, composite samples exhibit fairly high ductility (over 80%) with an increase in m values (0.34). The evaluation of the microstructures after applying isothermal tests and thermal cycling tests show that the thermally cycled samples have a widespread void formation and homogeneous plastic deformation in contrast to isothermally tested specimens.