Interfacial Microstructure In Joining Of Arc Sprayed Al-Zn Coating To AZ91D By Solid-liquid Compound Casting

Owing to the light weight,high strength and stiffness,good elastic modulus and shock absorption characteristics,magnesium and its alloys have been extensively applied in the automotive and aerospace industries,national defense military project,and 3C fields.However,they are easy subjected to sufficient corrosion,which serious limit them wider and further development.Arc spraying technology is one of the effective methods to improve the corrosion resistance of magnesium and magnesium alloy.In this paper,three different content Al-Zn pseudo alloy coatings was deposited on the surface of AZ91 D by arc spraying with Al-Zn twin-wire.In order to improve the bonding strength between coating and matrix,this paper tries to achieve the metallurgical bonding between Al-Zn pseudo alloy coating and AZ91 D substrate through the solid-liquid composite casting technology makes the arc spraying with the compound casting,at first,the mold surface was deposited a layer of Al-Zn pseudo alloy coating by arc spraying technology and then the molten magnesium was cast into the mold with Al-Zn pseudo alloy coating,so as to realize the combination of coating and substrate.This process can not only make AZ91 D surface with a layer of corrosion resistance of Al-Zn pseudo alloy coatings,but also changed the traditional arc spraying technology of combination way between substrate and coating,made the magnesium substrate and Al-Zn become metallurgical combination and formed the Mg-Al-Zn metal compounds between Al-Zn pseudo alloy coatings and magnesium matrix,which improve the wear resistance and corrosion resistance.A scanning electron microscopy,an energy dispersive spectroscopy,and X-ray diffraction were used to analyze the microstructure of the Al-Zn pseudo alloy coating and the Al-Zn/AZ91 D interface,analysis of traditional arc spraying Al-Zn pseudo alloy coating structure,and corrosion resistance of the coating were analyzed and studied.The main conclusions are as follows:(1)Al-Zn pseudo alloy coatings with different contents were deposited on the surface of AZ91 D magnesium alloy by Al wire and Zn wire with different diameters.The surface of AZ91 D magnesium alloy were sandblasted before arc spraying,the arc spraying deposition of Al-Zn coating and AZ91 D magnesium alloy pseudo alloy substrate achieve good mechanical anchor in the interface because the surface roughness increases.There without obvious voids and cracks between Al-54 Zn,Al-73 Zn and Al-86 Zn pseudo alloy coating and AZ91 D interface,and the microstructures were uniform.(2)By controlling the process parameters of arc spraying,the porosity of Al-54 Zn,Al-73 Zn and Al-86 Zn pseudo alloy coatings was very low,which were 3.9%,1.5%,and 1.3%,respectively.With the increase of Zn content,Al-Zn pseudo alloy coating porosity is lower,this is because the Zn low melting point,melting in arc heat under Zn have good filling performance,in the solidification front superimposed on coating has been deposited.(3)Through the analysis of the chemical element composition of the layered structure,it is found that the Al-54 Zn,Al-73 Zn and Al-86 Zn pseudo alloy coating are composed of a layer of Al rich phase and Zn rich phase alternating stacking.(4)The electrochemical performance test in 3.5% NaCl solution show that the corrosion potential of Al-54 Zn,Al-73 Zn and Al-86 Zn three kinds of pseudo alloy coating are higher than AZ91 D magnesium alloy substrate were-1.117 V,-1.126 V,-1.083 V.With the increase of Al content in the Al-Zn pseudo alloy coating,the corrosion resistance of the coating was also improved.The corrosion current density of the three kinds of pseudo alloy coatings was reduced by an order of magnitude compared with that of the AZ91 D substrate.(5)Through the solid-liquid composite casting process was successfully prepared Al-54Zn/AZ91 D and Al-73Zn/AZ91 D composite castings,the method not only makes the coating and substrate interface formed intermetallic compound transition layer for Al-Zn pseudo alloy coating with AZ91 D magnesium alloy metallurgy combination,but also keeps the advantages of wear resistance and corrosion resistance of coatings.(6)Al-54Zn/AZ91 D solid-liquid composite interface due to the diffusion of Mg element was formed in three different intermetallic compound layers,the layer(I region)adjacent to AZ91 D substrate was mainly composed of ?-Mg+Mg17(Al,Zn)12+?-Mg21(Al,Zn)17.The layer(III region)which was close to the Al-54 Zn pseudo alloy coating mainly consisted of ?-Al+ Al2Mg3Zn3.The intermediate layer(II region)was mainly consists of a single phase ?-Mg32(Al,Zn)49.(7)Al-73Zn/AZ91 D interface is composed of ?-Mg+Mg17(Al,Zn)12+?-Mg21(Al,Zn)17 in diffusion region,there are dozens of micrometer single phase structure?-Mg32(Al,Zn)49 near the edge of Al-73 Zn pseudo alloy coating.(8)The microhardness of the Al-54Zn/AZ91 D and Al-73Zn/AZ91 D interface diffusion region were significantly higher than that of AZ91 D magnesium substrate and Al-54 Zn and Al-73 Zn pseudo alloy coating.The layer I of Al-54Zn/AZ91 D have the same organization composition with the Al-73Zn/AZ91 D interface organization,but the hardness is less than the diffusion organization hardness of Al-73Zn/AZ91 D,this is because the Al-54Zn/AZ91 D diffusion layer I have more content of ?-Mg than Al-73Zn/AZ91 D interface organization.