Effect Of Friction Stir Processing On The Microstructure And Properties Of AZ31Magnesium Alloy

Friction stir processing(FSP) is a novel severe plastic deformation(SPD) technique andhas been successfully used in preparing metallic materials with fine-grained structure．Frictionstir processing was applied to AZ31magnesium alloy．The tensile properties were measuredthrough the tensile test and the microstructure and micro-fracture mechanism of the AZ31alloy were analyzed before and after processing．Separated Hopkinson Pressure Bar(SHPB)was used to perform on the compressed test of the AZ31magnesium alloy before and afterFSP．Through these means we can get the effect of FSP on the properties，microstructure，micro-fracture mechanism and dynamic properties of the alloy．The main results have beenobtained as follows：The whole processing area was composed of stired zone(SZ)，thermo-mechanicallyaffected zone(TMAZ)，heat affected zone(HAZ) and base material(BM)．Fine equiaxedgrains were obtained in SZ，and the average grain size increased with theincreasing in rotation speed and decreasing in advancing speed．The FSPed AZ31magnesium alloy experienced dynamic recrystallization when theadvancing speed was200mm/min and400mm/min and the rotation speed was less than1000rpm．The resultant microstructure was fine equiaxial grains with the average size less than7μm．Comparing with the alloy matrix，the strain strengthening effect of FSPed AZ31magnesium alloy was enhanced significantly and the plasticity was increased but the yieldstrength was decreased．The FSPed AZ31magnesium alloy obtained the best comprehensivemechanical properties when the advancing speed was400mm/min and the rotation speed was600rpm．Comparing with the alloy matrix， the dynamic yield strength of FSPed AZ31magnesium alloy increased in varying degrees，The FSPed AZ31magnesium alloy obtainedthe best shock deformation ability when the advancing speed was400mm/min and therotation speed was600rpm．The friction stir processing can induce the production of dislocation which obstacled the dislocation motion and refine the grain size.The results show that the gain size seemed to be the dominant factor on the shockdeformation ability of AZ31magnesium alloy，and the FSPed AZ31alloy is not sensitive tothe change of strain rate．...