Surface integrity and material removal mechanisms in high-speed grinding of Al/SiCp metal matrix composites

Abstract

SiC particle reinforced Al metal matrix composites (Al/SiCp MMCs) are typical difficult-to-machine materials due to the heterogeneous constituent. Poor surface integrity is commonly caused in conventional machining methods. To explore material removal mechanisms in high-speed grinding, this study carries out high-speed grinding (HSG) on an Al/SiCp MMC at a grinding speed from 30.4 m/s to 307.0 m/s, and assesses surface integrity including surface damage and subsurface damage (SSD) to explore how different grinding speeds take effect therein. The results reveal that improved surface quality is attained in HSG in which continuous and discontinuous dynamic recrystallization mechanisms govern Al grain refinement, and the latter is inclined to occur in the upper part of the ground surface. The distribution of the O-rich zone is closely associated with subsurface cracks. The workpiece ground at a higher grinding speed is with less damage than at a lower grinding speed due to the reduced O-rich zone. Three different layers in the subsurface below ground workpiece are identified based on various features, which are relatively narrower compared to that in low-speed grinding. The range of plastic deformation of the Al alloy matrix is suppressed in HSG because of larger Al grains and a reduced depth of lateral cracks in Al alloy matrix. Distinctly denser dislocation kinks formed at the boundary of SiC particles in HSG indicate the increased ductility of SiC particles. In HSG of Al/SiCp MMCs, strain-rate effect prevails for Al alloy matrix as a result of reduced ductility, and size effect plays the dominant role for SiC particles due to increased ductility, which facilitate reducing the property discrepancies between these two very different components. Therefore, an improved surface integrity of the Al/SiCp MMCs is realized through HSG. This study enhances the understanding of the surface and subsurface formation and material removal mechanisms in HSG of Al/SiCp MMCs, which can provide a theoretical basis and practical reference for achieving better surface quality for Al/SiCp MMCs and other composites machined by HSG.