Laser-assisted machining of SiCp/Al composites: Preheating history driven microstructure evolution and its role in material removal

Abstract

SiCp/Al composites are typical difficult-to-machine materials, and laser-assisted machining (LAM) is an effective approach to address their poor machinability. However, the intrinsic softening mechanism of material under the laser action is still unclear. The preheating history of LAM in which the workpiece temperature first rises and then decreases has also gone unnoticed. Understanding the interaction between laser preheating and the microstructure of SiCp/Al composites is beneficial to enhance the advantages of LAM. In this study, a novel molecular dynamics (MD) simulation model of SiCp/Al composites considering the laser preheating history is performed to analyze the dynamic evolution of microstructure from three perspectives: heating, cooling and cutting. The grain growth phenomenon in the Al matrix is identified by XRD and laser scanning (LS) experiments, and the degree of grain growth is controlled by the combination of scanning speed and laser power. The MD simulation indicates that the grain growth of Al matrix is achieved through disordering and recrystallization. In addition, it is observed in TEM experiments that high temperature arising from laser heating contributes to the annihilation of dislocations within the Al matrix. Ultimately, the nanoindentation experiments verify the material softening under the laser annealing effect. It is worth emphasizing that different preheating histories induce various microstructure, which in turn affects the softening degree of the material. The LAM experiments and simulation of SiCp/Al composites are performed, and the results demonstrate that different softening degree of the material leads to variation in the removal behavior, as reflected in the cutting forces and shear angles. This study is conducive to enhancing the comprehension of the material softening mechanism under the laser action and the material removal behavior under different preheating histories, which provides theoretical support for the rational control of LAM parameters.