The microstructure, hardness, residual stress, and friction and wear properties of 25CrNi2MoV steel with different particle diameters during shot peening strengthening were studied. Studies have shown that a grain refinement layer appeared on the surface of the material after shot peening. The shot peening intensity increased with increasing particle diameter; a greater shot peening intensity corresponded to a greater surface hardness of the material, the maximum hardness was 592 HV_0.2, and the residual compressive stress on the material surface was 725 MPa. A shot peening finite element model was established to accurately predict the residual stresses in the samples after shot peening. The prediction errors were 1.4–7.9%. The finite element model indicates that the maximum residual stress occurs in the subsurface layer. After shot peening, the wear resistance of the sample significantly improved, and the amount of wear significantly decreased. Therefore, shot peening can significantly improve the mechanical properties and wear resistance of high-strength steel, which increases the service life of parts.

In this experiment, the T-joint of a 6082 aluminum alloy was welded by metal inert gas (MIG) welding and a fatigue test was carried out at room temperature. The mechanisms of generating pores and of fatigue fracture in welded joints are revealed in the case of incomplete penetration. There are two main types of pores: pores that are not welded and pores that are near the upper weld line of the weld. During welding, bubbles in the molten pool are adsorbed on the surface oxide film that is not penetrated, and cannot be floated to form pores; since it is a T-shaped welded joint, the molten pool is overhanged during welding, thereby forming pores near the fusion line. The fatigue strength of the welded joint based on the S–N curve at 10⁷ cycles is estimated to be 37.6 MPa, which can reliably be predicted in engineering applications. Fatigue tests show that fatigue cracks are all generated in the pores of the incomplete penetration, and it and the pores form a long precrack, which leads to large stress concentration, and the fracture occurs under a small applied load. Grain morphology around the pores also has a large effect on the fatigue properties of the T-weld joint. In the weld’s fatigue fracture, it was found that the crack stable-extension zone exhibited ductile-fracture characteristics, and the instantaneous fault zone is composed of a large number of tear-type dimples showing ductile fractures.

In this paper the MIG welding is used for high-speed train 6005-T6 aluminum alloy welding experiments. The microstructure, micro-hardness, tensile property and fatigue property of base metal and welded joint have been analyzed with optical microscopy (OM), micro-hardness machine, scanning electronic microscopy (SEM), tensile test machine and fatigue test machine, respectively. It was found that isometric crystals exist in the welds. The crystals in heat affected zone are bigger than base metal's. The width of the heat affected zone is 25mm. There is softening zone in the heat affected because of the redissolution and separating out of strengthening phase, and the minimum micro-hardness is 50HV. The tensile strength of welded joint is 191MPa up to 67% of the base metal, and the fracture is ductile fracture. Sheet and rod strengthening phases, fatigue strips and secondary cracks exist in base metal fatigue fracture that has cleavage fracture and ductile fracture characteristics. River pattern, secondary cracks, and brittle fatigue stripes exist in welded joint fatigue fracture that is cleavage fracture.

In order to further enhance the wear resistance of the camshaft surface, this study conducted shot peening reinforcement on CF53 steel. The research involves the analysis of microstructure, microhardness, and residual stress evolution. Additionally, a pin-on-disk friction and wear test machine was used to investigate the influence of shot peening on the friction-wear characteristics of CF53 steel. The results show that a certain depth of plastic deformation layer is formed on the surface after shot peening, accompanied by an increase in surface roughness. With the increase of shot peening pressure, the surface roughness, microhardness, and residual stress values of the samples correspondingly increase. Shot peening treatment significantly improves the friction-wear performance of CF53 steel, with a reduction of 22.5% and 54.6% in the friction coefficient and wear rate for SP3 and SP4 groups, respectively, compared to untreated samples. The wear mechanism of untreated samples is characterized by severe fatigue wear with prominent features of plowing grooves and cracks. In contrast, the wear mechanism of peened samples shifts to fatigue wear dominated by delamination.