Influence Of Hot Deformation On Microstructures And Mechanical Properties Of Mg-Li-Al-zn Alloys

Magnesium alloys have lots of advantages, such as low density, high specific strength, excellent capacity of radiation. So they are widely applied in aerospace, transportation and electronics industries. Added by Li element, magnesium alloys get more lower density. It makes magnesium alloys have more advantages in the the lightweight development of aerospace, transportation and electronics industries.In this paper, the influence of heat treatment and hot deformation on Mg-12Li-2Al-1Zn alloy has been investigated. Furthermore, the hot deformation behavior of Mg-8Li-2Al-1Zn alloy was investigated by using hot compressive tests on a Gleeble-1500D thermal simulation test machine at523~723K and at the strain rates of0.01~10s-1. Meanwhile, The relationship among temperature, strain rate and flow stress was analyzed. The constitutive equation was established, and the hot process map of Mg-8Li-2Al-1Zn alloy was also calculated. This work can obtain the best hot deformation parameters, and provide the basis for the establishment of hot deformation process, such as extrusion, forging and rolling.Mg-12Li-2Al-1Zn alloy was the single β-phase alloy. In the processing of forging and rolling, Mg-12Li-2Al-1Zn alloy introduced dynamic recrystallization and grains refined. Mechanical properties were improved because as-cast defects disappeared and grains refined. To roll by30%,50%and70%deformation extent, the ultimate tensile strength is176,185and198MPa, the elongation is50%,41%and38%, respectively.The influence of solid solution and aging treatments on microstructure and mechanical property of Mg-12Li-2Al-1Zn was discussed. The results showed that Mg-12Li-2Al-1Zn alloy presented age hardening effet at50℃for1h. The highest microhardness value reaches111HV0.1, the tension strength is281MPa and the elongation is13%. XRD analysis result shows that the MgLi2Al phase appears and disperses in the gain which improves the strength of the Mg-Li alloy when the alloy is aged at50℃for1h. Overaging phenomenon happens quickly when the Mg-Li alloy is aged at the range of50~150℃. After solid solution and aging treatment, the fracture mode of the alloy translates from ductile fracture to brittle fracture, and finally to ductile fracture.Mg-8Li-2Al-1Zn alloy was composed of α-Mg and β-Li. The stress-strain curves of the alloy show the characteristics of dynamic recrystallization. The flow stress of Mg-8Li-2Al-1Zn alloy decreases with the increase of deformation temperature and the decrease of strain rate. Dynamic recovery and dynamic recrystallization are verified by the evolution of microstructure. The constitutive relation of Mg-8Li-2Al-1Zn alloy can be well described by hyperbolic-sine-type equation and Z parameter．The average values of the exponent n and the activation energy Q are4.62and139.35kJ/mol respectively. According to the established processing map, we find that the optimum parameters for hot working of the alloy are in the domains of523~573K and0.1~1s-1.