Research On Microstructure,Properties And Superplasticity Of Mg-2.65Li-7.05Al-2.08Zn-0.15Y Alloy

Magnesium-lithium alloy is the lowest density metal structural material,which has the advantages of good conductivity,heat conduction,ductility and so on.It is widely used in aerospace,military industry,electronic products and other fields.The strength of Conventional Magnesium-lithium alloy is low,and the strength can be effectively improved by adding Al element.Multi-directional forging is a kind of high efficient plastic deformation process for the preparation of fine-grained materials.In this paper,Mg-2.65Li-7.05Al-2.08Zn-0.15Y alloy plate was prepared by multidirectional forging and hot rolling.The microstructure,mechanical properties and Superplasticity of the samples in different states were analyzed and discussed.The main research contents and results are as follows:(1)The multi-directional forging with nine passes at stepwise decreasing temperature conditions was carried out.With the increase of the number of multidirectional forging passes,the grains is gradually refined,both the strength and the hardness are gradually increased before the sixth pass.The average grain size is 5.66?m of the sixth pass,and the strength is 278 MPa,the hardness is 80.6 HV.After the ninth pass,the strength and hardness is decreased.(2)The strength of the hot rolled sample is 295 MPa,the hardness is 82.3hv,and the strength of the annealed sample is 271.5 MPa.The grain boundary strengthening mechanism is the main strengthening mechanism of the hot rolled sample.XRD and TEM analysis show that Mg17(Al,Zn)12 particles and high density dislocations are distributed in the alloy.(3)High temperature tensile tests of Mg-2.65Li-7.05Al-2.08Zn-0.15Y alloy under different deformation conditions of deformation temperatures of-543?633 K and strain rates of 1.67×10-4?1.67×10-2 s-1 were carried out.When the deformation temperature is 573 K and the strain rate is 1.67×10-4 s-1,the maximum elongation is 290%.During high temperature deformation.dynamic recrystallization and cavity nucleation and growth take place.Dense fibrous cavities can effectively improve the elongation.(4)The thermal deformation constitutive equation of modified Arrhenius and Zerilli-Armstrong modified of Mg-2.65Li-7.05Al-2.08Zn-0.1 5Y alloy were constructed.The constitutive equation of superplastic deformation mechanism is established.The stress exponent n=3 and the activation energy Q=125 kJ/mol of superplastic deformation.