Study On Shot Peening Of SiC_w/Al Composite And Its Characterization

Metal matrix composites are widely used in industry because of their superior comprehensive performance. Shot peening is a mechanical surface process with wide application in industry. In order to further improve surface properties of metal matrix composites, different shot peening treatments were carried out on SiCw/Al composite in this work. The strengthening mechanism of shot peening with the aim of improving SiCw/Al composite surface mechanical property were revealed via investigating the influence of peening parameters on residual stress field and microstructure, the relaxation behavior of residual stress, the thermal stability of the microstructure and the mechanical properties of plastic deformation layer.The homogeneous and inhomogeneous shot peening model were built in this work with the aim of investigating the influence of peening parameters on residual stress field of SiCw/Al composites. The homogeneous model simulated results show the maximum compressive residual stress and compressive stress depth increase with increasing coverage. The higher the shot material density is, the deeper compressive residual stress depth and the bigger value of compressive stress can be obtained. Relative small shot diameter can induce higher surface compressive residual stress and maximum compressive residual stress. Relative big shot diameter can induce deeper compressive residual stress depth and maximum compressive residual stress depth. Increasing shot velocity can increase maximum compressive residual stress depth and compressive residual stress depth, but has little influence of surface compressive residual stress and maximum compressive residual stress. The homogeneous model simulated results show tensile residual stress exists in reinforcement and compressive residual stress exists in metal matrix as the yield strength and Young’s modules of SiCw are much higher than that of 6061 Al. This kind of residual stress distribution is benefit to surface mechanical property of SiCw/Al composite.Comparing with traditional shot peening, stress peening, variable warm peening and compound peeening can further improve the residual stress field and microstructure in order to promote the SiCw/Al composite mechanical property. Compound shot peening combines the positive effect of stress peening and variable warm peening, and has the most significant strengthening effect. The experimental results confirm that the higher the applied loadings and the temperature are, the more relaxation of residual stress is in SiCw/Al composite. The residual stress relaxation of peened SiCw/Al composite can be described by Zener-Wert-Avrami function. The residual stress relaxation activation energy is 135.1 kJ/mol and has close relationship with reinforcement property.The microstructure development of peened SiCw/Al was analyzed according to X-ray diffraction profiles method. The results show shot peening is an effective method to refine domain size, increase microstrain and dislocation density of surface layer. The initial surface texture is almost eliminated after shot peening treatment. According to the analysis of recovery and recrystallization behavior for peened SiCw/Al in different temperature conditions, the activation energy of the grain boundary migration, for the SiCw/Al and its monolithic alloy, are 250 and 232 kJ/mol, and their activation energy of microstrain relaxation are 226 and 217 kJ/mol, respectively. The movement of grain boundaries impeding by the reinforcements is the main reason why the recrystallization activation energy of the composite is higher than that of alloy.All shot peening treatment can increase the surface microhardness and residual stress filed intensity of plastic deformation layer for SiCw/Al composite. Meanwhile, microstructure of peened plastic deformation layer change towards the direction of surface mechanical property improvement. The precipitated phase Mg2 Si forms in the condition of certain temperature during shot peening process. The movement of dislocation is impeded by the pinning role of Mg2 Si, which can make the dislocation further multiplication and the dislocation movement impediment. The phenomenon can strengthen the improvement effect of material surface mechanical property.Stress strengthening and microstructure strengthening are the two kinds of strengthening mechanism of shot peening for SiCw/Al composite. Both of them play very important role in surface mechanical property improvement. The stress strengthening mechanism in nature is decreasing the actual loading level of material via surface compressive residual stress. The microstructure strengthening mechanism in nature is improving the material surface mechanical property via microstructure improvement. The reinforcements play an important role in these two kinds of strengthening effects and make the residual stress field and microstructure more stable in the condition of mechanical loading and temperature.