Micro-alloying And Deformation Mechanism Research Of AZ80Magnesium Alloy

The microstructure and properties of AZ80magnesium alloy with micro-alloying and deformation were investigated in this paper. Taking into account of the cost, the AZ80-RE magnesium alloys were prepared by adding Gd、Y and Nd as the micro-alloying elements. Grain refinement by mechanical stirring obtains uniform distribution of RE strengthening phase. And through some thermoplastic deformation processes, we finally acquire high performance magnesium alloys. The effects of RE on the microstructures and mechanical properties of both the as-cast and deformed AZ80alloys were studied. The research conclusions are as follows:(1) The results show that the appropriate rare earth elements can improve the microstuctures of as-cast AZ80magnesium alloy, the dendrite morphology reduced and the lamellar phase consisted by a-Mg and Mg17Al12appeared along the grain boundaries. AbRE phase as irregular blocks distribute in grains or at the grain boundaries, part of segregation. Compared with different addition methods, while adding mix of Gd and Nd, the mechanical properties are highly improved. When the addition is0.5%RE, the tensile strength and yield strength are better, but the elongation decrease.(2) According to the Miedema model, the calculated enthalpy of formation between Al and RE is greater than the Mg and RE, so RE and Al will combine to generate new phase rather than Mg and RE. Through the impact of RE on the aging process of the AZ80magnesium alloy, it has benefit for AZ80when adding the heavy and light RE mixed together.(3) Mechanical stirring prompt the Al2RE phase to be small and distribute homogenously. The particle size almost below5μm. Changing the stirring temperature, it proves that under640℃stirring, Mg17Al12phase scatter like ball shape and off-network, Al2RE particles are small and evenly distributed. The mechanical properties are also increased. By low-temperature mechanical stirring, we deduce that RE phase forms in advance when stirring under640℃, at that time, RE particles are small and evenly distributed by the force of stirring. When the temperature reach660℃or more higher, the RE phase forms at the final solidification process, so their size is much larger and part of it has segeration. (4) The microstructure of AZ80magnesium alloy after extrusion has pronounced fibrous tissue. AZ80precipitate a lot of Mg17Al12phase, but with the increase of RE content. Mg17Al12precipitates reduce and the grain size increases. Excessive RE phase weakens the effect of dynamic recrystallization. The highest tensile strength is345MPa when adding0.5%RE. With the increase of the RE content, the strength decline, but the elongation gradually increases. When adding2%RE acquires highest elongation that is12.2%which is40.2%more than AZ80. RE can improve the ductility of AZ80alloy.(5) The microstructure of rolled AZ80-RE alloys are relatively compact, Mg17Al12precipitates a lot and the grain size is small, the increase in RE content do not reduce the Mg17Al12phase’s precipitation, there are a lot of twins in the alloy. When adding0.5%RE, the alloy have highest tensile strength and elongation, that are385MPa and5.3%, respectively. The tensile strength is25MPa more than AZ80, it has a better comprehensive property.