In this study, an Inconel625-Ni60-Ni60/25%WC (Inconel625-Ni/WC) composite coating was fabricated on Cr12MoV steel by first-stage laser cladding, followed by second-stage laser remelting with various laser powers, and the better laser energy density of 25.0 J/mm² for laser remelting test was obtained by macroscopic morphology and microhardness analysis. The effects of laser remelting on the microstructure, microhardness, wear resistance, and impact resistance of the composite coating was systematically investigated by combining various characterization methods. The results showed that laser remelting did not cause the composite coating to produce new phases. The microstructure of the Ni/WC layer in the remelted composite coating was denser and finer, and the average grain size of the surface layer was reduced by 11.69%. The impact depth of laser remelting was about 2.0 mm. The average microhardness of the Ni/WC layer in the remelted composite coating increased by 5.9%, and the average wear rate of the surface was reduced by 50.12% compared with that before laser remelting. The wear surface of remelted composite coating exhibited abrasive wear, and the wear resistance was significantly improved. In addition, the impact toughness value of the remelted composite coating reached 5.15 J/cm², which increased by 87.96% compared with that before laser remelting. The impact resistance of the composite coating was further improved.

In this work, the purpose of the study was to explore the influence of laser shock peening (LSP) on the mechanical behavior and microstructural response of 40CrMo steel. The residual stress at depth direction and the microstructural evolution of 40CrMo steel specimens without and with LSP treatments were tested by residual stress tester and transmission electron microscopy (TEM). The microhardness at depth direction and the tensile properties at room temperature were measured. Moreover, the effects of LSP on the ability to resist wear of 40CrMo steel were analyzed, and the worn morphologies characteristics were observed by scanning electron microscope (SEM). The results demonstrated that LSP led to the surface residual stress convert from tensile stress to compressive stress, while the surface compressive residual stress tested parallel to the laser path of the specimen subjected to LSP reached −425 MPa. After the LSP process, the average surface microhardness reached 338 HV, which increased by 21.58% than that of the untreated sample. LSP could enhance the strength without losing plasticity significantly, while the average tensile strength reached 1165 MPa, and the fracture elongation reached 13.9%. After a friction and wear test, the mass loss of the sample after LSP treatment reduced by 27.5% compared to the original sample. The increase in dislocation density and the formation of deformation twins generated by LSP played a key role in enhancing the mechanical behavior of 40CrMo steel.

In this work, a welding solidification crack sensitivity test platform was established to study the effect of wire feeding speed (WFS) on solidification crack sensitivity during cold metal transfer (CMT) welding for AA6061 aluminum alloy. The test results show that as the WFS increased from 4 m/min to 5.5 m/min, the sensitivity of the solidification cracks also increased. With a further increase in the value of the WFS, the crack sensitivity decreased and eventually ceased to exist. A new perspective of the microstructure and crack propagation mechanics model was applied to understand the effect of WFS on solidification cracks. With the use of scanning electron microscopy (SEM) and a high-speed camera, it was found that as the WFS increased from 4 m/min to 5.5 m/min, the microstructure of the grain size changed from bigger to smaller, and the stability of the crystal microstructure was reduced. The crack propagation mechanics model was changed, which promotes crack propagation, increasing by 233%. When the WFS continued to increase beyond 5.5 m/min, the size of the crystal structure changed from small to big, the stability of the crystal microstructure was increased, the crack generation was suppressed, and the cracking rate was significantly reduced.

The automobile covering parts mold is a key piece of equipment in the automobile industry, and its drawbead is the core element that affects the life of the mold and the quality of the parts made. Due to the complex structure of the mold cavity for covering parts, there exist differences between material flow characteristics, load conditions, stress strain, failure forms and so on in the surface of different parts of its drawbead and the different directions of the same part of the drawbead, thus putting forward new requirements for material strengthening. For the differentiated lose efficacy forms of the dangerous end faces of the tension bars, this study carried out research into the effect of laser quenching–shock peening strengthening (LQ-LSP) on the organization, plastic deformation resistance and wear resistance of Cr12MoV steel. It was shown that the microhardness (722.30 HV) and residual stress (−383.84 MPa) of the specimens were further enhanced after laser quenching–shock peening composite strengthening. The residual austenite content of the specimen was reduced to 0.8%, and the eutectic carbide distribution morphology was improved. After three rounds of laser composite peening, the specimens had the smallest displacement of the nanoindentation load–depth curve, which exhibited the greatest nanohardness (20.0 Pa) and modulus of elasticity (565.25 Pa), while reducing the coefficient of friction (0.61) and surface roughness (0.152 Ra). The smooth and flat surface of the specimen with shallow and narrow plow grooves improved the resistance of Cr12MoV steel to plastic deformation and wear.