Aging Behavior And Corrosion Property Of Nanocrystalline Magnesium Alloy Prepared By Rotary Swaging

In this work,nanocrystalline WE43 and AZ80 commercial magnesium alloy samples were prepared by rotary forging.The aging behavior and corrosion property of the two alloys were studied respectively by X-ray diffraction analysis,scanning electron microscopy,transmission electron microscopy and other characterization methods,combined with Vickers hardness test,tensile property test and electrochemical test.The main conclusions are as follows:(1)The WE43 swaged nanocrystalline sample exhibited accelerated age-hardening than extruded coarse-grain sample at the initial stage of aging.After aging at 175℃ for 60 h,the nanocrystalline alloy exhibited the best mechanical property with ultimate tensile strength about 516 MPa,yield strength about 477 MPa and elongation to failure about 8.5%,which is much better than WE43 alloys prepared by other methods.When aging at 175℃,no precipitates were formed,and the segregation of rare earth elements at grain boundary was the main reason for the strength improvement.When aging at 225℃,precipitates were form along grain boundary.Compare with aging at 175℃,grain boundary segregation was weaker,grains grew up slightly,and the effect of aging strengthening also decreased.(2)After aging at 150℃ to 200℃,the swaged nanocrystalline AZ80 sample softened and its strength also decreased,as a result of static recovery and grain growth.After aging at 175℃ for 24 h,the yield strength,tensile strength and fracture elongation reached 336 MPa,415 MPa and15.8%,respectively.The aging behavior of the swaged nanocrystalline sample is significantly different from that of the extruded coarse-grain sample.Both continuous and discontinuous precipitation occurred in the extruded coarse-grain sample.However,continuous precipitation mainly occurred in the swaged nanocrystalline sample,and a large number of uniform spherical continuous precipitates were precipitated after aging at175℃.(3)In the process of soaking in 0.9 %Na Cl solution,the surface film of WE43 magnesium alloy remains stable after formation and has a good protective effect.Compared with coarse-grain sample,the surface film of nanocrystalline sample has a stronger and more durable protective effect,showing better corrosion resistance.It was found that during the corrosion process of WE43 magnesium alloy,the grain boundary acted as a corrosion barrier and hindered the corrosion expansion,and the surface film remained stable during the corrosion process,which resulted in a better protection effect.(4)In the process of soaking in 0.9 %Na Cl solution,the surface film of AZ80 magnesium alloy sample is extremely unstable and exhibited poor protection effect.Compared with coarse-grain sample,the surface film of nanocrystalline sample shows no protection effect and exhibits worse corrosion resistance.It was found that during the corrosion process of AZ80 magnesium alloy,the corrosion pits first appeared along the grain boundary,which accelerated the corrosion of the surrounding matrix as a high energy point.As a result,and the surface film was damaged extensively,losing its due protection.