Surface Modifications Of Mg-Gd-Y-Zr Alloys By Pulsed Electron Beams

This paper has investigated the effect of High Current Pulsed Electron Beams onsurface microstructures and properties of two Mg-RE alloys,GW83K(Mg-8%Gd-3%Y-0.5%Zr)and GW103K(Mg-10%Gd-3%Y-0.5%Zr).The main research contents are as followed:(1).The morphologies of these two Mg alloy treated by HCPEB becomes undulated and lots of craters and slip bands were formed,which is observed by using OM,EDS and SEM techniques.This is due to the drastic temperature variation at the top surface during the HCPEB treatment,which gives rise to the surface melting or evaporating and results in the formation of Mg droplets and craters at the surface.Besides,such a drastic temperature variation induces thermal stresses at the surface and results in surface plastic deformation and thereby causes the formation of slip bands on the treated surface.(2).Modified layers were formed when these two Mg alloys were treated by pulsed electron beam irradiations and the depth of the modified layers increases with the increase of pulses number,which is revealed by cross-section SEM observations.Grains within the modified layers were refined and large scale?-Mg₅(Gd,Y)precipitates were dissolved into substrate,which results in the increased Gd and Y contents within the modified layers.(3).XRD results show that the diffraction peaks of the?-Mg of these two Mg alloys shift after HCPEB treatments,which suggests a lattice distortion of?-Mg.This is due to the dissolution of Gd and Y elements into the?-Mg matrix and the formation of residual stresses in thetreated layer after the HCPEB treatment.(4).TEM observations demonstrate that the HCPEB treatment can refine the size of?-Mg₅(Gd,Y)and leads to the formation of nano?-Mg₅(Gd,Y)particles less than 10 nm.These nano precipitates are distributed along the grain boundaries and can inhibit the grain growth of Mg during the HCPEB treatment.(5).Cross section hardness profiles of the treated samples show that the hardness of the treated surfaces were strengthened after HCPEB treatment due to the refinement of?-Mg grains and?-Mg₅(Gd,Y)particles and the formation of residual stresses at the treated layers.(6).Electrochemical measurements demonstrate that both of the two Mg alloys treated by 5 pulses shows the best corrosion resistance.This is mainly attributed to the dissolution of Gd and Y into the melted surface layer,which help the formation of a protective oxide film on the HCPEB treated surface,leading to the improved corrosion resistance.