ANALYSIS OF THE TENSILE PROPERTIES AND FRACTOGRAPHY OF AS-CAST AND HEAT-TREATED 359-SIC-20P COMPOSITE

An experimental study of the heat treatment of 359-SiC-20p composite a nd its base alloy was made to determine the strength-ductility charact eristics under varying conditions of heat treatment. Microstructural o bservations revealed that addition of the SiCp reinforcement to the ba se alloy produced a more uniform and refined interdendritic microstruc ture compared to the latter. The tensile data obtained was analysed in terms of the theoretical models existing in the composite literature. Ultimate tensile strength (UTS)-log elongation relationships were obt ained to test the applicability of the quality index parameter, Q, to the present composite. From this analysis, it was found that all data points in the ageing temperature range 140-210 degrees C could be repr esented by a single line (cf. two lines in the case of 359 alloy), ind icating the important fact that the tensile properties of this composi te can be predicted/determined over the entire temperature range. The presence of the SiC particles was seen to accelerate the Mg2Si precipi tation kinetics, but not to alter it. Fracture mechanisms were determi ned from both the fracture surfaces and their longitudinal sections be neath the fracture surface, employing both optical and scanning electr on microscopy.