Research On The Plastic Deform Behavior Of Ultra-fine Grained Magnesium Alloy Prepared By Friction Stir Processing

AZ31 magnesium is one of the most widely used deformation magnesium alloy.It is significant to research on the plastic deformation behavior of ultra-fine grained magnesium,which can expand the application of magnesium.In this study,the ultra-fine grained AZ31 magnesium was prepared by friction stir processing(FSP).The nano-hardness and behavior were analyzed by nanoindention machine.The super-plasticity was studied with different temperatures at varied rates.The main conclusions were as follows:In nanoindentation test,the loading curves of FSP zones had better fit than that of basal metal(BM),which was related to the microstructure homogeneity.The maximum depth of BM was higher than those of FSP zones.Meanwhile,the maximum depth of BM,Stir zone(SZ),thermo-mechanical affected zone in advance side(TMAZ-AS)and thermo-mechanical affected zone in retreating side(TMAZ-RS)were 1244.9 nm,1156.6 nm,1148.3 nm and 1142.8 nm,respectively.The AZ31 magnesium exhibited indentation size effect with the decrease of loading,and the nanohardness at 5 m N was higher than other loadings.For the FSP specimens,the young’s modulus was constant with the change of load,while that of BM decreased with the loading increased.The estimation of compressive yield for BM and SZ zone was 0.595 GPa and 0.551 GPa.The strain hardening exponent of BM and SZ zone was 0.340 GPa and 0.406 GPa,and it fitted in with Tabor’s indentation theory.The microstructure of FSP AZ31 magnesium alloy was stable at high temperature and exhibited good super-plasticity at different temperatures and strains.At the different temperature,the elongation at the rate of 3×10-3 s-1,1×10-3 s-1 were higher than that of 1×10-2 s-1 and 3×10-4 s-1.At different rates,the elongation was better,when the temperature was 400 ℃.At the strain rate of 3×10-4 s-1 and 450℃,the elongation was 1090.8%.The main deformation mechanism was grain boundary slip(GBS),which resulted in the exhibition of holes.The fracture of tensile specimens resulted from the holes.