Investigation Of Laser Shock Processing On Microstructure And Corrosion Resistance Of AM50 Magnesium Alloy

Magnesium alloys with many excellent characteristics,have been widely used in aerospace,automotive,computer,electronic communications,military and other fields.However,in the damp environment,magnesium alloys are prone to electrochemical corrosion,in the case of load susceptible to stress corrosion,resulting in destructive accidents.Laser shock processing(LSP)is a new type of surface strengthening technology,which can improve the microstructure of the material,reduce or delay the nucleation and expansion of the crack,and improve the corrosion resistance of the metal material.Now,the effect of LSP on the corrosion resistance of magnesium alloys and the microstructure and properties of magnesium alloys along the depth lack system researches.Thus,the effect of LSP on the corrosion resistance and microstructure of AM50 magnesium alloy was studied in this paper.Some main conclusions and achievements have been obtained:(1)Three-dimensional analysis model was established by ABAQUS finite element simulation software to research the influence of two LSP paths on residual stress field distribution of AM50 magnesium alloy,compare and analyze the advantages and disadvantages of the two paths.The results showed that the magnitude and depth of the residual compressive stress of the top surface of the sample subjected to the double-sided alternate impacts were slightly smaller than the corresponding value of the top surface induced by double-side sequential impacts,while the bottom surface subjected to the double-sided alternate impacts were larger than the corresponding value induced by double-side sequential impacts.With the impact layers increasing,the difference of the magnitude and depth to residual compressive stress to the top surface and bottom surface treated by double-sided alternate impacts became smaller.However,the difference on the top surface and bottom surface treated by double-side sequence impacts became larger.(2)The effect of the LSP layers and concentration solutions on the stress corrosion resistance of AM50 magnesium alloy was investigated.In the concentration of 3.5% sodium chloride corrosion solution,compared with original samples,the tensile strength,the maximum strain and the fracture time of LSPed samples were obviously improved,which indicated that the stress corrosion resistance was improved.And with the layer of LSP increasing,the stress corrosion resistance was further improved.Whether the basal or LSPed sample,in the corrosion solution with three concentrations of 3.5%,7% and 14%,the stress corrosion resistance was decreased with the concentration of corrosion solution increasing.However,no matter the concentration of corrosion solution is,the stress corrosion resistance of the LSPed samples were obviously improved comparing with basal sample.(3)The effect of the LSP layers and concentration solutions on the electrochemical corrosion resistance of AM50 magnesium alloy was investigated.In the concentration of 3.5% NaCl corrosion solution,comparing with the basal sample,the electrochemical corrosion resistance of the LSPed sample had been improved obviously.With the increase of LSP layers,the electrochemical corrosion resistance was further improved,but the magnitude of improvement was reduced.In three concentrations of 3.5%,7% and 14% corrosive solution,with the concentration of corrosive solution increasing,whether the LSPed samples or the basal sample,the corrosion resistance was improved.However,compared with the basal sample,the corrosion resistance of the LSPed sample was obviously improved no matter how much the concentration of the solubility was.(4)The effect of LSP with different layers on the microstructure and properties of magnesium alloy in the depth direction of the magnesium alloy was studied: When the AM50 magnesium alloy was LSPed with one cover layer,the results showed that the micro-hardness of the surface increased by 19%,the residual compressive stress reached-225 MPa,and the grain size was refined to 10 ?m.Meanwhile,the depth of improvement micro-hardness region and the depth of residual compressive stress were fundamentally the same as the depth of grain refinement.When the impact layers was increased to 2,the micro-hardness,residual compressive stress and grain refinement were further improved,and the depth of the improvement areas were consistent while the magnitude of improvement is reduced.In summary,the research of this paper provided the theoretical and experimental basis for the influence of LSP on the corrosion resistance and microstructure of magnesium alloy.