Chip formation and morphology in cryogenic machining of Al-SiC composites

This study investigated the influence of cryogenic cooling on chip formation and morphology during the turning of aluminum–silicon carbide (A359/SiC-20wt%) composites using an uncoated tungsten carbide cutting tool. The primary objective was to enhance the cutting conditions and improve the overall efficacy of the machining process for aluminum composite materials. Compared with dry machining, cryogenic cooling significantly altered the chip formation process, producing shorter and less curled chips at all tested cutting speeds. The rake and dual cooling strategies proved to be the most effective in terms of chip breakability, despite the relatively unchanged tool-chip contact length (chip ratio increased up to 25% and chip curl increased up to 20%). Cryogenic cooling also led to a reduction in average chip thickness, particularly with the dual cooling strategy, contributing to improved material removal efficiency. Microstructural analysis revealed that under cryo-cooling conditions, the hard SiC particles were distributed more uniformly within the chips, in contrast to the particle redistribution along the shear bands observed in dry cutting. Chip separation is primarily facilitated by the formation and propagation of cracks and microcracks along the matrix-particle interface, leading to noticeably frayed chip edges and improved breakability. The study also examined the effects of cutting speed and cooling strategy on chip characteristics, such as chip curl diameter, average chip thickness, chip compression ratio, and shear angle. For example, the chip curl diameter decreased by 18% with cutting speed and the shear angle increased by 16%. These findings contribute to the understanding of machining aluminum matrix composites under cryogenic conditions and provide insights for optimizing cutting parameters to enhance the machining performance, tool life, and surface quality.