Research Of Dynamic Recrystallization In Hot Torsion Deformation Progress Of Mg-Gd-Y-Zn-Zr Alloy

Mg-13Gd-4Y-2Zn-0.5Zr alloy,like other Rare Earth heat-resistant magnesium alloy,also have all the unique advantages.At present,the research of rare earth heat resistant alloy is mainly through the hot compression deformation,but its microstructure and properties evolution in the process of torsion deformation is rarely studied.The thermal simulation experiment(hot torsion)was conducted on Mg-13Gd-4Y-2Zn-0.5Zr alloy using Gleeble-3500 to study the high-temperature mechanical behavior and thermal map was established.The effects of different deformation conditionson including temperature,strain rate and strain on microstructure evolution and mechanical properties were analyzed.Simultaneously,the phenomenon of dynamic recrystallization during hot torsion deformation was researched and predicted,and the critical strain of DRX was established and verified by the microstructure evolution.Then the kinetics model and different DRX mechanisms under differnent temperature were analyzed.The influence of deformation degree,deformation temperature and strain rate on the Vickers microhardness was analyzed by measuring the microhardness of the specimen from the center to the edge.The equivalent stress-strain curves of Mg-13Gd-4Y-2Zn-0.5Zr alloy which had been homogenized showed the representative rheological characteristics od DRX.The peak of equivalent stress decreased with the increase of temperature and the decrease of strain rate.Based on the equivalent stress-strain curves,the thermal map was established,and the optimum deformation condition is determined,namely 440?~480?,0.001s-1~0.01s-1.However,at 350?,1s-1,the crack was produced,which is not conducive to deform.The relationship between the critical strain and Z parameters of DRX at the edge of Mg-13Gd-4Y-2Zn-0.5Zr magnesium alloy during torsional deformation was ?=3.76593×10-3 Z0.08412.And the dynamic recrystallization occured when the strain of the alloy was the critical strain.The kinetics model of DRX was:It was found that the deformation temperature played an important role in the mechanism of dynamic recrystallization,and the strain rate and deformation degree had important influence on the dynamic recrystallization volume fraction.The continuous dynamic recrystallization(CDRX)was the mainly DRX mechanism at 400?,when temperature increased to 450? and 480?,the grain boundary arch and serrate grain boundary appeared,and the dynamic recrystallization was dominated by discontinuous dynamic recrystallization(DDRX).The fraction of DRX increased with the increase of the temperature and the distance from center as well as the decrease of strain rate.Dynamic recrystallization grain size increased with the increase of the temperature,but first decreased and the increased with the increase of the strain rate.The Vickers microhardness after hot torsion were higher than that of homogenization,and the Vickers microhardness increased with the increase of distance from center.The Vickers microhardness of Mg-13Gd-4Y-2Zn-0.5Zr alloy after hot torsion decreased with the increase of the temperature and the decrease of strain rate.When the strain rate was 0.01s-1,there is little difference between the Vickers microhardness values in the temperature range of350?~450 ?;and when the temperature was 450?,the Vickers microhardness performed bigger under 0.01s-1 than that of other strain rates.