| Mg-Li alloy, as the ultra-light alloy, currently is the lightest metal structural material. It not only has low density, high specific strength and specific stiffness, but also has good machinability and damping performance and recyclable etc. properties. Mg-Li alloy is increasingly widely used in the aerospace, transportation, communications, electronics, military and other requiring lightweight components areas, and is the most favourite to be the important lightweight, high strength, environmentally friendly materials in 21st century. Although the Mg-Li alloy with excellent performances have attractived many domestic and foreign scholars and a lot of researches on it have been carried out, there are still some drawbacks such as low strength and poor corrosion resistance existed, which restricts its further development and application. In this thesis, as the strength of the Mg-Li alloy is relatively low, select the Mg-Li-Al-Zn alloy as the based alloy, and add Ce-rich mischmetal (RE) and Ce element in the Mg-5Li-3Al-2Zn alloy. The influences of RE and Ce elements on the microstructure and tensile properties of Mg-5Li-3Al-2Zn have been studied.In this paper, Mg-Li alloy was prepared by vacuum melting furnace under the ambient of pure argon, and processed by extrusion deformation. Using optical microscopy (OM), scanning electron microscopy (SEM), energy spectrum analysis (EDS), X-ray diffraction and tensile and other measures to study the effects of RE and Ce elements on microstructure and tensile properties of as cast and extruded Mg-5Li-3 Al-2Zn alloy. The solution treatment was also conductived to study its effect on the microstructure and tensile properties of Mg-5Li-3Al-2Zn-xRE.The results show that:â‘ The Mg-5Li-3Al-2Zn alloy mainly composes of a-Mg and AlLi phases, after adding RE and Ce elements respectively, the Al2RE/AI3RE phases and Al2Ce/Al3Ce phases form and distribute in the matrix grain boundaries and intra grains, and the amount of the increases gradually with the addition of RE and Ce elements.â‘¡The additions of RE and Ce elements can improve the tensile strength of the as cast Mg-5Li-3Al-2Zn alloy, but about its microstructure, besides generating compounds, the additions of RE and Ce elements have no obvious effect of grain refinement; tensile results show that LAZ532-1.5REå'ŒLAZ532-1.0 Ce alloys present excellect properties respectively. â‘¢The dynamic recrystallization occurrs during the extrusion process and resultes in the formation of fine grains in alloys, the tensile properties of alloys are substantially improved. Mg-5Li-3Al-2Zn-0.5RE presents the best tansile properties, the tensile strength and elongation are as high as 294.1MPaå'Œ26.64%; The grain size of extruded alloy varies obviously with different RE additions.â‘£After solution treatment, due to the amount of the solute atoms in matrix increases, the tensil properties of cast alloys are significantly improved, wheras the tensile properties of extruded alloy decline owing to the grain growth.The analysis suggestes that RE and Ce elements can generate Al-RE/Al-Ce compounds with the aluminum element in alloys. An appropriate amount of Al-RE/Al-Ce compounds can play the better dispersion strengthening effect. However, The excess formation of Al-RE/Al-Ce compounds not only consumes Al elements in the alloy resulting in the reduction of the solid solution strengthening effect, but also prones to arise the aggregation of compounds which does not benefit to the tensile mechanical properties of the alloy. Solution treatment can increase solute atoms in the matrix and improve the tensile properties of as cast alloy owing to the better solid solution strengthening effect, but the solution treatment deteriorates the tensile properties of extruded alloys as the result of the grain growth. The addition of RE can also change the fracture mechanism of the alloy and make the fracture pattern of the alloy transit from the brittle fracture to the brittle and ductile mixed fracture. |
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