Study On Tensile Deformation Behavior Of Extruded AZ80+0.4%Ce Magnesium Alloy At Elevated Temperature

In this paper,the tensile behavior of extruded AZ80+0.4%Ce magnesium alloy along the extrusion direction was studied by INSTRON 3382 universal material stretching machine,and the constitutive equation was established.The thermal processing map of strain of 0.15 was drawn and the safety zone and the destabilizing zone were discussed.The microstructure and fracture mechanism of the hot deformed specimen were analyzed by ZIESS PL-A662 optical microscope and SU5000 scanning electron microscope.The main conclusions as follows:(1)During the hot tensile deformation of extruded AZ80+0.4%Ce magnesium alloy,the increase of temperature makes work hardening weaken but is helpful to the occurrence of dynamic recrystallization but the increase of strain rate makes work hardening enhanced but is not conducive to the full dynamic recrystallization,Therefore,the increase of temperature or the decrease of strain rate can make the peak stress reduced.(2)According to the Arrhenius constitutive model,the constitutive equation is established,which can be used to describe the relationship between flow stress,temperature and strain rate during hot tensile deformation of extruded AZ80+0.4%Ce magnesium alloy.The value of deformation activation energy Q is 190.169KJ/mol and the constitutive equation of thermal tensile stress is:(3)The high power dissipation area of the safety zone appears in the range of deformation temperature of 380-420℃ and strain rate of 0.01-0.0005s-1,which is the best deformation zone for magnesium alloys.When the magnesium alloy is deformed under the deformation condition of this area,microstructure of magnesium alloy can be refined.Because the dynamic recrystallization is not easy to occur,the plastic processing is difficult to carry out in the flow instability zone.(4)When the AZ80+0.4%Ce magnesium alloy is thermally stretched,the effect of strain rate on dynamic recrystallization mode is that at 340℃ the twin recrystallization occurs at high strain rate and rotate the dynamic recrystallization occurs at low strain rate.(5)During the deformation of AZ80+0.4%Ce magnesium alloy,there are a variety of cracks,such as void-like,twisted along the twins,as well as microporous aggregation type cracks.Their formation mechanism is different,But they generally appear in the easily deformed fine grain area.(6)With the decrease of strain rate,the fracture mechanism of the alloy is changed from brittle-ductile fracture to ductile fracture at 300℃.When the strain rate is constant,with the increase of deformation temperature,the fracture characteristics of the fracture are becoming more and more obvious.The study of the microstructure of the fracture shows that because of the absence of recrystallized grains the serious stress concentration in the twin boundaries and grain boundaries leads to the specimen is generally cracked along the twin or grain boundary but it is easy to crack in the fine dynamic recrystallization grain region in the event of dynamic recrystallization.(7)During the thermal tensile deformation of AZ80+0.4%Ce magnesium alloy,β phase appears at 300℃ and 340℃.The stress concentration can provide more energy for the precipitation of β phase,so β phase is easy to precipitate in the place where the stress concentration is generated.