Study On Shot Peening Of Aluminum Borate Whisker Reinforced Aluminum Matrix Composite And Its Characterization

Metal matrix composites have received widespread attention in the scientific fields and have been wildly used in industrial fields owing to their low density,high wear resistance,high specific strength,and excellent hightemperature stability.Shot peening is a simple and effective treatment of surface strengthening.By introducing compressive residual stress field and improving the microstructure,the material fatigue performance can be significantly improved.In the present study,the aluminum borate whisker reinforced aluminum matrix composite was shot peened by a variety of shot peening processes.The residual stress field distribution,surface morphology,and microstructure of the deformation layer of the composite were characterized by different methods,such as optical microscope(OM),X-ray diffractometer(XRD),scanning electron microscope(SEM),transmission electrons microscopy(TEM),etc.The results of different shot peening processes show that as the layer depth increases,the compressive residual stress of the shot peening layer increases firstly and then decreases,and finally stabilizes to a low level of residual tensile stress at the core of the material.For the multiple shot peening process,the greater the shot peening intensity,the larger the maximum value of compressive residual stress of the deformation layer,and the deeper the corresponding affected depth.The results of pre-stress shot peening show that under the same peening intensity,preloading a certain tensile stress on the sample can effectively increase the maximum compressive residual stress and the depth of the compressive residual stress field.And the greater the pre-stress,the more obvious the improvement effect.The warm peening process blasted the sample at an initial temperature of 200°C.Compared with the peening samples with an initial temperature of room temperature,the maximum compressive residual stress and the overall affected depth of the compressive residual stress after warm peening are both increased significantly,25% and 27% respectively.The research on the morphology of the shot peening layer shows that the shot peening processes are able to increase the surface roughness,and the greater the shot peening intensity,the greater the surface roughness.When the shot peening intensity is too large(0.52+0.10 mm N),microcracks will be introduced on the sample surface.The results of TEM observation show that high-density dislocation entanglement appeared in the samples after shot peening,and the sub-grain size was highly refined,showing typical microstructural characteristics after shot peening.The results of Xray diffraction linear analysis also confirm this.According to the calculation of Voigt unimodal analysis,it was found that the domain size of the surface layer after shot peening increases with the increase of the layer depth,microstrain and dislocation density show the opposite trend,they decrease with the increase of the layer depth,and finally both tend to be consistent and stable at the level before shot peening.The characterizaion results of the mechanical properties of the shot peening layer show that multiple shot peening,pre-stress shot peening,and warm peening can effectively improve the microhardness of the surface layer.The microhardness has a maximum value on the surface,and it decreases with the increase of the layer depth,and finally returns to the level before shot peening.The main strengthening mechanisms of aluminum borate whisker reinforced aluminum matrix composites after shot peening are stress strengthening and microstructure strengthening.The compressive residual stress field introduced by shot peening can significantly increase the allowable external load alternating stress,drive the source of fatigue cracks to the subsurface layer,and effectively inhibit the propagation of micro-cracks to improve the fatigue performance.Relying on the refinement of the domain size and the increase of the dislocation density in the surface layer after shot peening,the mechanical properties of the shot peening layer are improved.