Surface characteristics of machined aluminium metal matrix composites

This paper investigates the effect of cutting parameters and particulate properties (volume fraction and average particulate size) on the microhardness variations of the aluminium matrix beneath the machined surface. Orthogonal cutting tests were carried out on different aluminium matrix composites reinforced with varying volume fractions and average sizes of alumina particulates. Characterization of the machined subsurface was made using optical, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The metallographic analysis revealed severely damaged machined subsurface with numerous geometrical defects and plastically deformed aluminium matrix. This study also yielded some interesting findings on the influence of particulate volume fraction and average size in altering the microhardness in the aluminium matrix. The lower the reinforcement volume fraction and the coarser the particulates, the higher are the variations in matrix microhardness. The microhardness measurements on the aluminium matrix beneath the machined layer showed higher values when machining under wet conditions with reduced depth of plastically deformed zone.