Study On Crack Propagation Behavior Of Hypereutectic Al-14wt%Si Alloy

Up to now,the research on fracture mechanism of hypereutectic Al-Si alloy is focused on the macroscopic characterization.The study on crack propagation behavior of hypereutectic Al-Si alloy in the fracture process is less.Aiming at the problems of the crack initiation and propagation process of hypereutectic Al-Si alloy is unclear,Al-14wt%Si alloy is taken as the research object.By using the high temperature laser confocal scanning microscope with tensile function,the process of crack propagation is observed in situ.The crack initiation location,propagation path and the propagation rate in different phases and the influence law of the crack propagation behavior of silicon with different morphologies are investigated.The results show that the cracks initiate on the surface of large silicon and the cracks propagate step by step in primary silicon.The corresponding relationship between the initiation location and growth process of crack and the size and morphology of silicon phase is clarified.It reveals that the larger the size of silicon phase,the more likely the crack initiation is on the surface of silicon phase,the smaller the size of silicon phase,the crack initiation mode gradually changes to the interface crack between silicon phase and substrate.The cracks in silicon phase mainly propagate in linear way,and the step and bifurcation mode are the auxiliary.After the crack of silicon phase,the interface cracking between silicon and substrate is chosen as the propagation path,and then it expands to the sharp angle of silicon phase,then into the substrate.Other cracks directly into the substrate and to the nearby silicon phase.For the fracture of hypereutectic Al-Si alloy,the size of silicon phase is the main factor and the influence of morphology is small.The results show that the propagation rate of crack is up to 200-606?m/s when the crack propagates linearly in the silicon phase,the growth rate will be reduced by 90% when the scale is stepped.The fastest propagation rate of crack along the interface of silicon is4.97?m/s,the propagation rate in ?(Al)substrate is only 0.98?m/s.