Laser Cladding Of Cu-Zr-Al Alloy Coating On The Magnesium Alloy

Magnesium alloys are considered as "ideal engineering materical for 21th century due to low density, high specific strength and rigidity, as well as good machining property, dimensional stability, and shock absorption. However, the application of Mg alloys is limited because of high sensitivity to oxidation, low corrosion resisitance and bad mechanical property. In this paper, Cu-Zr-Al alloy coatings were prepared by laser cladding improve mechanical and chemical properties of Mg alloy.The Cu-Zr-Al alloy system was designed by means of cluster line criterion. The mother alloy of Cu58.1Zr35.9Al6 with the high GFA was prepared by copper mold vacuum arc furnace, and milled into powders with the size of 200 mesh by ball grinder, which were selected as laser clad materials. The Cu-Zr-Al alloy coatings on the surface of AZ91HP were prepared by broad-beam and spot-beam laser claddings, respectively. The microstructure and properties of the coatings, as well as the influence of processing parameters on them, were investigated by modern micro-analysis techniques and perfermence analysis facility.The experimental results show that the coatings prepared by broad-beam laser cladding broad-beam consisted of ZrCu, CusZr3, Cu10Zr7 , Cu51Zr14 , and a-Mg phases, of which the reticulation-like ZrCu phase continuously distributes around grey zone constituted by the Cu8Zr3, Cu10Zr7, and Cu51Zr14 phases. The bonding type between the clad and heat effected zones is non-flatness combination. The heat affected zone was composed of dendrite α-Mg+ Mg17Al12 eutectic, and the grow direction of the eutectic is closely related to.temperature gradient and convection of melting pool. The hardness, Young's modulus, wearing resistance, and erosion resistance of the coatings were higher because of the enhancement of multi -intermetallic compounds.Compared with the coatings obtained by broad-beam laser cladding, the microstructure of the coatings prepared by spot-beam laser cladding obviously changes because of extremely higher heating and cooling rates. XRD analysis shows that the spot-beam laser clad layers consisted of amorphous, Cu8Zr3, and Cu10Zr7 phases, of which the content of the amorphous phase increases with scanning velocity, and the maximum is about 60%. The grain size is 15~60nm by means of calculation. The coatings have no contrast morphology under the corroding of 5%HNO3 +5%HC1 +3%HF. The bonding type between the clad and heat effected zones is non-flatness combination. The microstructure of heat affected zone is closelyconnected with scanning velocity. When scanning velocity was less than the critical value, the heat affected zone is composed of dendrite a-Mg+ MgnAln eutectic. When the scanning velocity was above it, the microstructure is equiaxed a-Mg solid solution. The hardness, Young's modulus, wear resistance, and corrosion resistance of coatings are higher due to the recombination action of amorphous and intermetallic compounds.