Investigation On High Strength Ultra-light Magnesium-Lithium Alloy

Magnesium-lithium alloys are widely used in the military defense,civilian products and other fields because of its light weight,high strength and high stiffness and other characteristics.However,magnesium-lithium alloys have low corrosion-resistant and mechanical properties,which greatly limits its practical application in the field of industry.Therefore,a certain process to increase their strength under the premise of low density of magnesium-lithium alloys has became one of the focuses of magnesium-lithium alloy.In this paper,the Mg-5Li-3Al-2Zn-0.2Y(?-phase),Mg-8Li-3Al-2Zn-0.2Y(?and ? phases)and Mg-11Li-3Al-2Zn-0.2Y(?-phase)alloys are designed.The effects of rolling temperature and heat treatment on the microstructure and mechanical properties were studied.On this basis,in order to obtain better mechanical properties,the aluminum content is increased to 5wt.%and the effect the extrusion and heat treatment process on microstructure and mechanical properties of Mg-xLi-5Al-2Zn-0.2Y(x=5wt.%,8wt.%,11wt.%)alloy were investigated.Meanwhile the effect of aluminum content on the solution of AlLi phase and mechanical properties was discussesed.At the same time,the effects of the addition amount of Al-Ti-B refiner on the microstructure and mechanical properties of Mg-xLi-5Al-2Zn alloy were studied.The main conclusions of the research are as follows:(1)The microstructure of Mg-xLi-3Al-2Zn-0.2Y alloy is mainly composed of a phase and a small amount of AlLi phase,Al₂Y phase and MgAlLi₂ phase after rolling.With the increase of Li content,the a phase decreases gradually,and precipitated ? phase and the amount increased gradually with the increase of Li content.The microstructure of the alloy containing 8wt.%Li was mainly composed of a and ? dual phase,the microstructure of the alloy containing lithium 11wt.%Li was mainly composed of ? single phase;(2)After rolling,the grains elongated into strips along the rolling direction,and occurred dynamic recrystallization.The tensile strength of Mg-5Li-3Al-2Zn-0.2Y and Mg-8Li-3Al-2Zn-0.2Y alloys gradually decreased with the increase of the rolling temperature.However,the tensile strength of the Mg-11Li-3Al-2Zn0.2Y alloy first increases and then decreases with the rolling temperature.(3)Static recrystallization was occurred during the heat treatment of Mg-8Li-3Al-2Zn-0.2Y alloy.When the rolling temperature was 300?,it was completely transformed into equiaxed grains.The tensile strength and yield strength increased with the increase of heat treatment temperature but the elongation decreased.The highest tensile strength was 229.1MPa an elongation was 12.7%.Mg-11Li-3Al-2Zn-0.2Y alloy appeared abnormal grain growth at the heat treatment temperature of 250?.The tensile strength increased with the increase of the heat treatment temperature,the tensile strength was up to 250MPa and the elongation was 5.6%.Mg-111i-3Al-2Zn-0.2Y has better mechanical properties.(4)The dynamic recrystallization of the alloy was occurred with the increase of extrusion temperature.The tensile strength increased gradually with the increase of extrusion temperature of Mg-8Li-5Al-2Zn-0.2Y alloy and Mg-11Li-5 Al-2Zn-0.2Y.The mechanical properties of Mg-5Li-5Al-2Zn-0.2Y alloy were not affected by the extrusion temperature.The optimal extrusion temperature was 200?.The tensile strength and yield strength was increased with the increase of annealing temperature in the Mg-8Li-5Al-2Zn-0.2Y and Mg-11Li-5Al-2Zn-0.2Y alloys.At 300?,the mechanical properties of the alloys are the best.The tensile strength of Mg-8Li-5Al-2Zn-0.2Y was 235.1MPa,the elongation was 24.4%.The tensile strength of Mg-11Li-5Al-2Zn-0.2Y alloy was 329.2MPa and the elongation was 5.3%.(5)The as-cast microstructure of Mg-xLi-5Al-2Zn(x=5wt.%,8wt.%,11wt.%)alloy was significantly refined after the refiner Al-Ti-B was appropriately added.The as-cast microstructure was not refined the 1.0wt.%Al-Ti-B was added.The microstructure of the alloy was slightly refined after extrusion and the mechanical properties of the alloy were improved,but the magnitude was not large.