Study On The Mechanical Properties And The Microstructure Of Typical Magnesium Alloy At Elevated Temperature

Continuous casting process is simple process, short production cycle, saving energy, low cost and high efficiency. Using continuous casting process , the thin cast-ing strip of magnesium alloy can obtain the desired microstructure and good mechanical properties.But the crack was easily produced in continuous casting process.It is very important to set reasonable parameters.Based on the typical magnesium alloy tensile and compression tests during high temperature,This paper studied the mechanical behavior of magnesium alloys, microstructure evolution and fracture morphology into the other,to provide the theoretical basis for processing technology of magnesium alloy。The high temperature deformation behaviors of AZ31,AZ61and AZ80 extruded rod were studied by using Gleeble-1500D thermal simulator.The result showed that the elastic modulus and strain hardening exponent of magnesium alloys decreased.the strength and plasticity of magnesium alloys decreased until 0 with temperature increasing, the flow stress of magnesium alloys decreased at lower deformation rate, a slightly increased in elongation. It can be obtained that the zero ductility temperature and zero strength temperature of magnesium alloys according to the temperature elongation curves and the temperature- tensile strength curves.The analysis of tensile fracture surfaces of magnesium alloys revealed that deformation temperature and strain rate had been a major impact on the evolution of microstcture.During relatively low temperature, dynamic recrystallization was very obvious and grain was small and uniform. During high temperature defongmation, grains grew and the second phase molted. In the same temperatue and lower deforma- tion rate, dynamic recrystallization was more obvious and the gain was refined.Through the analysis of magnesium alloy tensile fracture surface,it showed that the fracture morphology mainly was ductile fracture with ductility nests in relatively low temperature. As temperature increased,the fracture morphology mainly was quasi- cleavage fracture with torn edge.In high temperature, the fracture morphology mainly was intergranular brittle fracture.The analysis of SEM,EDS and XRD showed that Mg17Al12 precipitated on fracture surface and precipitation increased with tempe-rature increasing,especially in grain boundary.In the same temperature and higher deformation rate, Mg17Al12 precipitation increased. As Mg17Al12 molten,micro-cracks produced, connected along grain boundaries,and fractured.The high temperature compressive study of AZ31 magnesium alloys congtinuous sheet by Gleeble 1500D showed that steady flow stress reduced from 36.5MPa at 15% deformation to 31MPa at 35% with the deformation increasing during 450℃.during the same deformation, the maximum of steady flow stress was 42.6MPa in 10°,the minmum was 30MPa in 0°.It was relatively small changes in flow stress during 500℃in different directions and deformations.The average of steady flow stress was about 35MPa during 450℃,27.5MPa during 500℃.The microstructure of AZ31 magnesium was consist of dynamic recrystallization grain and large grain .With deformation increasing,the dynamic recrystallization was more fully, wider area, recrystallization grain refinement,the size reduced from the 5μm to 3μm.As the temperature elevating, dynamic recrystallization was more fully.