Study On Technology And Process Of High Entropy Alloy Coating On Magnesium Surface Prepared By Friction Stir

Magnesium alloy has high specific strength,good machinability and excellent anti-magnetic interference performance,and it is widely used in aerospace,transportation,electronic technology and other industries.However,the shortcomings of low hardness,poor wear resistance,and corrosion resistance limit the further development of magnesium alloys.The high entropy alloy has excellent abrasion resistance and corrosion resistance,which can make up for the shortcomings of magnesium alloy.In this paper,it was come up with that a high entropy alloy coating is prepared on the surface of magnesium by friction stir processing,which took the influence of process parameters on the microstructure and properties of the prepared cladding materials as the research focus.The cross section,surface microstructure and element distribution of high entropy alloy coating material on the surface of magnesium were discussed in detail.At the same time,the mechanical properties and corrosion resistance were studied,which provided experimental basis and theoretical guidance for the preparation of high entropy magnesium surface alloy coating with wear and corrosion resistance.In this paper,Al Co Cr Fe Ni_2.1 high entropy alloy with good mechanical properties and corrosion resistance was selected as the coating material,and the high entropy alloy coating on the surface of magnesium was prepared by friction stir processing.According to the macroscopic morphology and interfacial structure,the pressure of the surface of magnesium high entropy alloy coating was determined to be 0.4 mm.On this basis,The microstructure and properties of the surface of magnesium high entropy alloy coatings prepared at different rotation speeds and processing speeds were studied by using XRD,OM,SEM+EDS,friction wear testing machine and electrochemical workstation and other equipment.Firstly,the rotation velocity had an important effect on the macroscopic forming and microstructure of high entropy alloy coating material on the surface of magnesium.When the processing speed was 100 mm/min and the rotation speed was 1500 rpm,the surface forming of the coating material was better and the defects were less and the length of the diffusion layer was 7.4μm.When the processing speed increased to 150mm/min,the thickness of the diffusion layer also increased to 10.0μm.The width of the diffusion layer widened with the increase of the machining speed.Part of the magnesium elements was transferred transition to the high entropy alloy coating,and the diffusion of the high entropy alloy element was not obvious.The distribution of FCC phase and B2 phase in high entropy alloy coating was uniform,and there was a small amount of circular aggregation of B2 phase.Secondly,the properties of high entropy alloy coating materials on the surface of magnesium under different process parameters were studied.When the processing speed was 100 mm/min and the rotation speed was 1500 rpm,the shear force and bonding strength of the cladding interface were the maximum.The surface hardness of high entropy alloy coating material on the surface of magnesium was increased by26%～31%compared with that of cast high entropy alloy,and by 7 times compared with that of magnesium alloy.The hardness analysis of cross section showed that the hardness of high entropy alloy coating was much higher than that of magnesium matrix,and the hardness of magnesium alloy near the coating increased slightly.The high entropy alloy coatings had high wear resistance,and the friction coefficients were all in the range of 0.50～0.65,while the friction coefficients of magnesium alloys were0.3045.It was found that the wear marks of magnesium alloy had obvious deep grooves and stratification,and the wear marks were relatively straight,showing obvious bonding wear.The width of the wear marks on the surface of the coating changed obviously,mainly shallow grooves,friction wear type was abrasive wear,and the resistance to friction wear was good.The corrosion resistance of high entropy alloy coating material on the surface of magnesium was greatly improved compared with magnesium alloy substrate.Under the processing speed of 100 mm/min and rotation speed of 1500 rpm,the coating material increased the corrosion potential of magnesium alloy from-1.25964 V to-0.3648 V,and the maximum phase Angle reached 70°,which was much larger than the phase Angle of the magnesium matrix of 25°.Fitting circuit results showed that the passive film circuit resistance increased to 340.4Ω·cm²,while magnesium alloy was only 43.04Ω·cm².The corrosion morphology shows that the surface corrosion of magnesium alloy was more serious,while the corrosion of high entropy alloy was concentrated in B2 phase,and the overall corrosion trace was less.The mechanical property and corrosion resistance of high entropy alloy coating on magnesium alloy surface was analyzed.It was concluded that the mechanical property and corrosion resistance of magnesium matrix surface can be significantly improved by preparing Al Co Cr Fe Ni_2.1 high entropy alloy coating on magnesium alloy surface.Finally,ABAQUS software was used to simulate the temperature field of high entropy alloy coating on the surface of magnesium prepared by friction stir processing.It was found that the peak temperature was lower than the melting point of high entropy alloy.It was also observed that the peak temperature did not appear in the center of the mixing head,but around the mixing head.By comparing the cross sections of the cladding layers under different rotation speeds,it was found that the peak temperature increased with the increase of rotation speed.At the same time,the high temperature area was concentrated near the mixing head,and with the increase of distance from the center,the temperature gradually decreased until it reached the room temperature.