Mg-gd-y - Zr Magnesium Alloys, Performance Research

Mg-8.0%Gd-3%Y-0.5%Zr(1#),Mg-10%Y-3.0%Y—0.5%Zr(2#), Mg-12%Gd-3.0%Y-0.5%Zr(3#),were prepared.High temperature compression experiment of two alloys were performed on deformation simulation test machine.The true stress-strain behaviors of the experimental alloys were investigated with various strain rates at different deformation temperatures.The relationship of true stress,strain rate and temperature during the plastic deformation was studied.The microstructure of the experimental alloys was observed by optical microscopy(OM),X-ray diffraction analysis(XRD),transmission electron microscopy(TEM) and scanning electron microscopy(SEM). The high temperature tensile properties of the alloys were studied respectively in different temperature.The results indicate that:1) Two different kinds are presented on the true stress-strain behaviors of the experimental alloys.At a low temperature,the work hardening plays a main role on the plastic deformation of the alloys. At intermediate temperature,both of the work hardening and dynamic recovery may cause such phenomena.The effects of such two mechanisms keep balance so that the flow stress keeps a steady value. At high temperature,the flow stress increases to a maximum value at first and then decreases to attain a steady state finally.Such flow behavior is characteristic for hot working accompanied by dynamic recrystallization.2) It is found that the stress-strain was affected obviously by the strain rates and deformation temperature.The peak flow stress was larger with the increasing of the strain rates at the same temperature, and was smaller with the deformation temperature at the same strain rates.3) Deformation of the investigated alloys is very difficult at below 300℃because of the work hardening.In this temperature range,the specimen breaks at different degree.Only in above 350℃temperature range,dynamic recovery and dynamic recrystallization can act so that it is propitious to deformation of the investigated alloy. 4) SEM microstructure analysis of the experimental alloys revealed that:in our experimental alloys,the element Gd and Y mainly exists in grain boundaries.The containing RE phase is Mg₅Gd and Mg₂₄Y₅ through XRD analysis.5) After extrusion deformation and T6,the high temperature ultimate tensile properties of the experimental alloys were as follows: the ultimate tensile strength and elongation of 1# alloy were 320MPa, 8.9%;268MPa,15.4%;192MPa,27.6%respectively in 150℃,250℃, 300℃;the ultimate tensile strength and elongation of 2# alloy were 345MPa,7.3%;283MPa,12.1%;245MPa,25.4%respectively in 150℃,250℃,300℃;the ultimate tensile strength and elongation of 3# alloy were 420Mpa,6.6%;320MPa,11.3%;252MPa,23.4% respectively in 150℃,250℃,300℃;The values of the tensile properties indicate that the experimental alloys have good combination properties of temperature.6) The precipitates did not change in the process of high temperature extruding at 300℃in 3# alloy,were stillβ′phase.Deformation resistance reduced because of the distribution ofβ′phase pre-stretch mesh gradually into the direction parallel to the deformation of the strip distribution,so the ultimate tensile properties of the experimental alloys decreased quickly.Both the strength and heat-resistant declined because of the precipitate phases melting partly in the process of high-temperature stretch.