Laser Remanufacturing of ZM6 Rare Earth Heat Resistant Mg Alloy in an Ultra-low O2 Content Atmosphere and the Resultant Physical and Mechanical Properties
W-B. Ren, S-Y. Fang, P. Wu and Y-J. Wang
The ZM6 Mg alloy gearbox is difficult to remanufacture by laser cladding due to excessive element burning, powder deflagration and loose structure. The homogeneous alloy layer process and method by laser cladding in ultra-low O2 content offer both great economic and environmental benefits, and are proposed in this paper. The results reveal that there are no internal defects such as loose or gas hole in the laser remanufacturing zone, the microstructure fineness density of the remanufacturing zone is close to that of the original ZM6 Mg alloy substrate, the contents of Mg, Zr, Nd, Zn and other major elements remain basically consistent with that in the substrate. The layer and substrate are mainly composed of equiaxed crystalline grains, which are obviously finer than those of the substrate; furthermore, the precipitated granular or microspherical intragranular and intergranular strengthening phases, mainly composed of α-Mg and β-Mg12Nd phase composition, are more uniformly dispersed. The heat affected zone (HAZ) is not obviously coarsened. The microhardness from top layer to interface ranges from 56.4 to 63.2 HV0.1, higher than that of the other parts of the substrate. The maximum bending load borne by the layer is between 152 and 167 N, with bending strength ranging from 205 to 220 MPa and coefficient of friction (COF) from 0.26 to 0.42. Relevant mechanical properties meet the remanufacturing standards (GB/T 40737-2021).
Keywords: Fibre laser, ZM6 Mg alloy, O2, gearbox, remanufacturing, laser cladding, microstructure, microhardness, bending strength, coefficient of friction (COF), heat affected zone (HAZ)