Research On Heat Resistance And Strengthening Mechanism Of Mg-Gd-Y-Sm-Zr Alloys

Magnesium alloy has already widely used as structural materials under thecondition of low temperature. However, in order to meet the requirement by using athigher temperatures（above200℃）, rare earth magnesium alloyis developed and heatresistance is better. The magnesium alloy containing high gadolinium has become aresearch hotspot in recent years. In this paper, Mg-Gd-Y-Sm-Zr alloy is studied toimprove the microstructure and the elevated temperature mechanical properties bymeans of solid solution and aging.This paper integrated use various research methods of metallic material, mainlyincluding metallographic analysis, scanning electron microscopy with energydispersive X-ray analysis, X-ray diffraction analysis, tensile properties and elevatedtemperature creep test measures. The microstructure and mechanical properties ofexperimental alloys are observed and analyzed. The results show that themicrostructures of as-cast and aged alloys mainly consist of α-Mg matrix, Mg₅Gd andMg₂₄Y₅. As the temperature increases, the tensile strength of the alloy first increasesand then decreases, obtaining the maximum（313.5MPa） at250℃.The elongationincreases with increasing temperature. By means of solid solution strengthening,precipitation strengthening and fine grain strengthening, the mechanical properties ofMg-Gd-Y-Sm-Zr magnesium alloys under room and elevated temperature areimproved, and to improve the ductility of the alloy. The mechanical properties of Mg-Gd-Y-Sm-Zr alloys are excellent compared with WE54alloy.The tensile fracture morphology of Mg-Gd-Y-Sm-Zr alloys shows obviouscleavage platform at room temperature. The surface of tensile fracture appearsquantities of micro-void coalescence and tear ridges with the increasing temperature.The fracture trends of the alloys gradually transform from brittle fracture to ductilefracture. Through the theoretical calculation, calculation values of planar mismatch between α-Mg matrix phase and Mg₅Gd are extremely small. Mg₅Gd can be anexcellent heterogeneous nucleus in the range of effective nucleation which caneffectively refine grain sizes. The creep resistance of Mg-Gd-Y-Sm-Zr alloys is betterthan that of WE54alloy, which is a successful commercial application magnesiumalloy. The creep mechanisms of the series alloy at the range of200℃to300℃arecontrolled by dislocation climbing towards dislocation cross-slip. With the increase oftemperature and stress, creep activation energy of Mg-Gd-Y-Sm-Zr alloys is closer todiffusion activation energy of pure magnesium, which is about80kJ/mol.