Study of machining induced surface defects and its effect on fatigue performance of AZ91/15%SiCp metal matrix composite

Abstract

The quality of surface generated in a peripheral milling of AZ91/SiCp/15% for varying machining conditions and its effect on the fatigue performance are investigated in this study. The machined surface quality was evaluated through roughness measurements and SEM micrographs of the machined surface. Tensile tests were performed to measure the mechanical properties of the composite. Subsequently, fatigue life of milled specimens was measured through axial fatigue tests at four loading conditions. Optical and SEM/EDS micrographs of the fractured surface were studied to identify the crack initiation site and propagation mechanism. Specimens machined at a lower feed rate of 0.1 mm/rev was found to have excellent surface finish and consequently higher fatigue life. At 0.3 mm/rev, the presence of feed marks and other surface defects resulted in a drastic decrease in fatigue life. Five distinct regions were identified on the fractured surface, particle fracture along and perpendicular to the surface, voids in the matrix due to particle debonding and pull out and typical ductile failure of matrix with embedded SiC particles.