Research On The Multidirectional Forging Process And Superplasticity Of Mg-6.4Li-3.6Zn-0.37Al-0.36Y Alloy

Magnesium alloy is the lightest structural material in engineering application,and it is also known as the three light metal structure materials with aluminium alloy and titanium alloy.Magnesium alloy has high specific strength,high specific stiffness,good damping ability,good dimensional stability,good machinability,easy to recycle,etc.and it is known as "the green engineering metal structure material of the 21st century".Magnesium lithium alloy is the lightest metal structure material,with high specific strength,high specific stiffness,good electromagnetic shielding,good damping vibration and many advantages such as good machining performance in aviation,spaceflight,automobile,electronics and other fields has a broad application prospect.Metal superplastic forming in recent years has become more widely used in industrial production,the technology can be used for processing complex shape,large deformation of workpiece,but the superplastic requires initial microstructure has fine grain size,and multidirectional forging technology as a representative of severe plastic deformation process can be prepared with fine grain or ultrafine grain structure material.Therefore,the study on the multidirectional forging process and superplasticity of magnesium lithium alloy has an important role in improving the performance of magnesium lithium alloy and extending its application field.This paper analyses the multidirectional forging process and superplasticity of Mg-Li alloys,which based on the new dual phase Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy.At the same time,we research the micro structure and mechanical properties of the two kinds of Mg-Li alloy mentioned above.The main researches and conclusions are summarized as follows:(1)Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy processed by multidirectional forging under isothermal temperature conditions and obtained its 1st?3rd?6th?9th?12th pass forgings.The room temperature mechanical properties of 1st,3rd,6th,9th and 12th pass alloy was studied,the ultimate tensile strength of the Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy reachs the maximum after six passes multi-directional forging,and the elongation reachs the maximum after nine passes,it has the ultimate tensile strength of 208MPa and the elongation of 38.7%.(2)The multidirectional forging and rolling Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy has the ultimate tensile strength of 286MPa and the elongation of 31.8%;the annealed Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy of 523K×1h has the ultimate tensile strength of 217MPa and the elongation of 40.2%with two phase average bandwidth of 12.08 ?m.This result show that the properties of Mg-Li alloys can be improved by the plastic processing of multidirectional forging and rolling.(3)The multidirectional forging and rolling Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy along the rolling direction of 0 °,45 ° and 90° has the ultimate tensile strength of 286MPa,280MPa and 274MPa,the elongation shows a decreasing trend:31.8%,27.1%and 10.8%.That means rolling can improve rolling 0° direction tensile strength and elongation.(4)In order to study superplasticity of Mg-6.4Li-3.6Zn-0.37Al-0.36Y alloy,the high temperature tensile test was conducted at the temperature from 473K to 623K and the strain rate from 1.67×10^-4s^-1 to 1.67×10^-2s^-1,The maximum elongation obtained at the condition of 573K,1.67×10^-4s^-1 was 327.9%.Based on the true stress-strain curves,the influences of temperatures and strain rates on flow stress were studied.Finally,the evolutions of microstructures and cavities during superplasticity deformation were studied.(5)The constitutive equation of thermal deformation and superplastic deformation was built,besides the values of stress exponent(n),and deformation activation energy(Q) were calculated.