Cui Zeqin

TIG Cladding + Laser Remelting of ZrAlNiCu Amorphous Coating

Abstract The present investigation focused on a new amorphous coating preparing technique which combined the advantages of both TIG arc and laser beam. After Zr 63.8 Ni 17.2 Al 11.4 Cu 7.6 powder bed was cladded on carbon steel surface by TIG arc, the coating was remelted using a CO 2 laser. The microstructure, the phase composition, the microhardness and the corrosion resistance of the present coating were analyzed. TIG arc helps the coating achieve a good bonding with substrate and a homogenous solidification. While laser beam contributes to a quick cooling rate to form an amorphous structure. The coating microstructure is complex, consisting of crystalline phase and amorphous phase. The XRD demonstrates a higher amorphous volume fraction of the present coating compared with traditional laser cladding. The present coating is 1330 MPa higher in microhardness, 0.07 V higher in corrosion potential and more than 10 times lower in corrosion current than traditional laser cladding.

Laser Surface Melting and Strengthening Magnesium Alloy far from Equilibrium

Abstract In order to obtain extremely rapid solidification structure far from equilibrium, the surface of AZ31B magnesium alloy was melted by CO2 laser, while the samples were extremely rapidly cooled in liquid nitrogen. The microstructure, the performance and the strengthening mechanism of the laser melted layer were investigated. The results show that grains of the melted layer are highly refined and the grain size is nearly uniform. The melted layer contains α-Mg and β-Mg17Al12, but β-Mg17Al12 which distributes along the grain boundary is few. Because of strengthening mechanisms of fine grains, super solid solution and dislocation, microhardness HV of the melted layer is up to 1400 MPa. Wear loss of the melted sample cooled in liquid nitrogen is about 50% less than that of the untreated sample and the melted sample cooled in air, and wear resistance of the melted layer is improved obviously. Impacting fracture morphology indicates that there is a trace of plastic deformation, thus, improving plasticity and ductility.