Microstructure And Properties Of DC-PMIG Cladding Al-Si Composite Layer On AZ91D Magnesium Alloy

Magnesium is part of the most abundant mineral resources in the world,with abundant reserves in the earth's crust.Magnesium alloys are known as “21st Century Green Engineering Materials” because of its advantages such as low density,good plasticity,easy processing and recycling etc.However,the poor corrosion resistance and low hardness of magnesium alloys restrict their performance advantages.DC pulsed metal inert-gas welding(DC-PMIG)is a relatively mature method,which is easy to apply in large-scale mechanized production.Using the technology to improve the properties of magnesium alloys is significant for expanding the application range of magnesium alloys.ER4043 alloy welding wire was used as the cladding material,and DC-PMIG was used to prepare the Al-Si composite layer on the surface of AZ91 D magnesium alloy.Simufact.welding software was used to simulate the thermal process of cladding,and the temperature field in the cladding process with different heat input was simulated.Based on this,the heat input and process parameters were selected and optimized.The results show that numerical simulation scheme 1~3,that is,the heat input of surfacing welding is 875 ~1281 J/cm,the cladding layer is well bonded to the matrix and the dilution rate is low.The heat input range obtained by numerical simulation is further optimized to set different procedure parameters for testing and obtained samples with different heat input.The microstructure and phase composition of the samples was observed and analyzed by optical microscopy,scanning electron microscopy,and x-ray diffractometry.The microhardness and corrosion resistance of the samples was measured by microhardness tester and electrochemical workstation.The results show that the surface forming and porosity with different heat input samples is different.The main components in the cladding layer are ?-Al solid solution,Al-Si eutectic and Mg2 Si.There is transition zone between matrix and cladding layer,the heat input directly affects the thickness of the transition zone.There are many kinds of intermetallic compounds in the transition zone,which are mainly Al12Mg17,Al3Mg2 and Mg2 Si.The microhardness ofsamples with different heat input has been improved compared with the matrix(50~70 HV0.1).The polarization curves and data analysis obtained by electrochemical corrosion experiments show that the self-corrosion potential of the matrix is-1467 m V,which is lower than the self-corrosion potential of the cladding layer with different heat input.With increasing the heat input,the self-corrosion current density of the cladding layer increases,and the corrosion resistance deteriorates.It is concluded that a millimeter-thick Al-Si composite layer with good surface forming can be prepared on the surface of a magnesium alloy within a certain range of heat input by the DC-PMIG.Among them,lower heat input is beneficial to reduce the porosity,reduce the thickness of the transition zone,reduce the self-corrosion current density of the cladding layer and thus improve its corrosion resistance.Therefore,the optimal heat input is 1062 J/cm,i.e.current 59 A,voltage 18 V,and moving speed 10mm/s.