The LPSO Phase Evolution And Properties Of Rare Earth Magnesium Alloy After Hot Torsional Deformation

Compared with the hot compression and stretching,the material has no obvious shape changeto achieve a large strain during the thermal torsion simulation test.The influence of friction of the deformation can be avoided then ithas the wellshape stability.No matter what kind of strengthening method,the influence of second phases of alloy to its mechanical cannot be ignored.LPSO phase,as a new type of reinforced phase,since it was discovered became more and getting attention because of its special structure and excellent performance.In this paper,the Mg-13Gd-4Y-2Zn-0.5Zr magnesium alloy deformed by hot torsion using Gleeeble-3500 thermal simulation machine at different temperatures and different strain rates.The experimental temperature were 350?,400?,450? and 480?,the strain rates were 0.001s-1?0.01s-1?0.1s-1 and 1 s-1.Form the stress-strain curves,at the same strain rate,the lower the temperature,the less time was required to reach the peak stress and the faster of speed.But the corresponding peak stress and the steady flow stress were higher than others.At the same temperature,the peak stress increases with the increase of strain rate.The increase rate of peak stress was constant at 400? and 480?.The deformation constitutive relationship wasestablished.The test results of XRD show that the alloys at different torsional deformation parameters have the same phase: ?-Mg,Mg12 ZnY phase(LPSO phase)and Mg3Zn3Y2 phase.The two forms of LPSO phase were bright lumps and gray lamellar.After the deformation,the diffraction peaks of the second phase were substantially unchanged,which indicates that the volume fraction of these phases is almost constant with different torsional parameters,and that the second phase has high thermal stability.Most of the grains after torsion were refined as the temperature increases.At the lower temperature,the evolution of the second phase(LPSO phase)was mainly kinked,and the kink was starting from the grain boundary.At the elevated temperature,the evolution of the LPSO phase was mainly broken and decomposition.And the phenomenon of broken and decomposition were more obvious when the higher of the temperature.When the value of the strain rate was high,the evolution of LPSO phase took place mainly kinded.There were little amount of dynamic recrystallization phenomenon at high temperature.When the value of the strain rate was low,there were sufficient times for deformation.The LPSO Phase was produced from grain boundary and then grown into the grain.Twisted stripe were distribution along the ?-Mg grain.At the elevated temperature and low strain rate,the LPSO phase broken decomposition and deformation were more obvious.And the grain size after dynamic recrystallization was finer.The grain size was 32?mat 450?and =0.01s-1.In addition,the second phase was broken and dynamic recrystallization more and more obvious with the increase of strainafter torsion.Compared with the hardness values of Mg-13Gd-4Y-2Zn-0.5Zr magnesium alloy after homogenized,the hardness values after torsional deformation were increased with the increase of the radius.The hardness value showed an increasing trend with the increase of the strain rate.The increase of hardness values were corresponding obvious besides of hardness values at =0.01s-1.Especially,when the strain rate is 0.01s-1,the hardness value,taking into the efficiency and performance,are corresponding ideal.In contrast to the effect of strain rate,the effect of temperature on hardness is that the hardness value decreases with the increase of temperature.At 350?,400? and 450?,the hardness values were almost the same at the same strain rate.But it is not ideal at 480?.