The Laser Surface Cladding Of AZ91D Magnesium Alloy With Al+Al₂O₃ Powders

In this article, we have carried out laser cladding experiments of Al with different weight percentage of Al₂O₃ composite powders on the surface of AZ91D magnesium alloy substrate through a 3kW crosscurrent type of CO₂ laser apparatus. A proper material system and laser cladding parameters were ascertained by the comparison of analyses basing on the microscopic and macroscopic qualities of different cladding layers. By the means of OM, SEM, XRD EDS, etc. different layers' phase constitution and microstructure were observed and analyzed, the mechanism of Al₂O₃ enforcement was also expatiated: Through a kind of disc-pin tribological wear experiment machine, we carried out tribological wear riments on the surface of AZ91D and Al₂O₃ with different weight percentage of composite coatings, tribological wear mechanism was also discussed basing on tribological wear configuration of variant wear experiment samples. Experiments of laser cladding samples, and the erosion mechanism were discussed too. In the end, we made some useful discussion of different cladding layers' corrosion behavior by the way of loss curves.Laser cladding parameters have great effect on microstructure, macro-configuration and the capability of the cladding layers. Under the cladding parameters of P=1.5kW,ν= 800mm/min, D=3mm, we obtained cladding coatings with good surface quality, fine microstructure, low dilution, high microhardness and good metallurgical combination interface with AZ91D substrate.The microstructure analysis results showed that, from the surface of the cladding specimen to the substrate, there are three distinct areas: the cladding area, the bonding area and the heat-affected area in the substrate. The different solidification character parameters it takes on different microstructure in the cladding layers. The typical microstructure was the typical extension growth on the plane basis at the bottom of the layers, cellular crystals near the bonding area, dendrite crystal in the middle of the cladding layers and fine equi-axed crystals on the top of the layers.Laser cladding layers mainly consists of Mg,Al12Mg17,Al₂O₃, The new hard phase which composing of Al₂O₃ and self-confusion alloy element enhanced the cladding layers along with the vehemence solid solution intensification and the remaining stress.Tribological wear experiments result shows the wear capability of Al+Al₂O₃ is 3 times as high as that of the AZ91D substrate. Coatings' corrosion current density is far less than that of the AZ91D substrate, which manifests the corrosion velocity of AZ91D far lower than that of the Al₂O₃ coatings.