稀土钇对铸态Mg-8Li-3Al-3Zn合金显微组织和力学性能的影响

镁锂(Mg-Li)合金是现今最轻的金属结构材料,在航空航天及交通运输等领域具有重大的应用价值.但铸造镁锂合金绝对强度低限制了其发展和应用.在Mg-Li二元合金中添加铝(Al)、锌(Zn)和稀土元素钇(Y)三种强化元素制备Mg-Li-Al-Zn-Y五元铸态镁锂合金来提高镁锂合金的力学性能.利用X射线衍射仪(XRD)、扫描...

Effect of Y on microstructure and mechanical properties of as-cast Mg-8Li-3Al-3Zn alloy

The magnesium-lithium alloy is the lightest metal structural material and has great application value in the fields of aerospace and transportation at present.However,the development and application of as-cast magnesium-lithium alloy are greatly limited because of the low absolute strength.Three strengthening elements of aluminum(Al),zinc(Zn)and rare-earth element yttrium(Y)were added to obtain the as-cast Mg-Li-Al-Zn-Y alloy.The purpose is to use alloying to enhance the mechanical properties of Mg-Li alloy.The phase composition,microstructure and mechanical properties of as-cast Mg-8Li-3Al-3Zn-xY(x=0,1)alloy were compared and analyzed by X-ray diffractometer(XRD),scanning electron microscope(SEM)and mechanical properties testing to reveal the reinforcement and fracture mechanism of rare-earth element Y on as-cast Mg-8Li-3Al-3Zn alloy.The results show that the microstructure of the as-cast Mg-8Li-3Al-3Zn alloy mainly consists of matrixα-Mg,AlLi and MgLi2Zn phases.With adding 1%Y(mass fraction),the AlLi phase disappears and a large amount of high-temperature hard phase Al2Y enrich at the primaryα-Mg grain boundary.Moreover,the microstructure is significantly refined.Comparing with Mg-8Li-3Al-3Zn alloy(134.40 MPa,96.46 MPa and 7.5%),the Mg-8Li-3Al-3Zn-1Y exhibits an optimum combination of tensile properties with the tensile strength,yield strength and elongation of 189.99 MPa,128.2 MPa and 7.8%,which are improved by about 41.4%,32.9%and 4%,respectively.The improvement of the mechanical properties is attributed to the secondary phase and grain refinement strengthening.By analyzing the fracture morphology,the fracture mode of as-cast alloy is changed from cleavage fracture to quasi-cleavage fracture.