Study On The Proparation And Properties Of Mg-Li-RE Alloys

The goal of the dissertation research is to obtain high-performance wrought Mg-Li alloys. The main research content is the effects of RE elements in Mg-Li alloys. The relationships among the composition, structure, deformation technology and properties of Mg-Li alloys are comprehensively researched. In this dissertation, the effects of Ce in Mg-Li binary alloy and in Mg-Li-Al ternary alloy, the effects of Y and Sn in Mg-Li-Al ternary alloy, the aging behavior and the electrochemical behavior during corrosion of Mg-Li-Al-Ce alloy were all researched.In the research about the effects of Ce in Mg-8.5Li alloys, the results show that, Ce exists in alloys in the form of Mg₁₂Ce which mainly locates at the grain boundary and phase boundary. Ce has refining effects on alloys, and it makes the amount aphase reduce and makes the amount ofβphase increase. With the increase of Ce content, the strength and hardness increase, while the elongation percentage decreases. The refinement and second-phase strengthen of Ce cause the improvement of mechanical properties. The mechanism for the refinement of Ce in Mg-8.5Li alloy is the constitutional supercool at the solid-liquid boundary and the formation of Mg₁₂Ce.Ce in the Mg-Li-Al alloy exists in the form of Al₂Ce. Adequate Ce content has the effects of refining and secondary-phase strengthening for alloys. The refining effect attributes to the congregation of Ce at grain boundaries and the formation of Al₂Ce.The effects of extrusion on the microstructure and mechanical properties of Mg-Li-Al-Ce alloys were also investigated. Extrusion process can improve the mechanical properties of Mg-Li-Al-Ce alloys. The dynamic recrystallization of Mg-8.5Li-3Al alloys takes place during extrusion process at 523K. In the research of the effects of rolling percentage on the microstructure and properties of Mg-8.5Li-1Al-1Ce, the dynamic recrystallization ofβphase happens during the rolling process. With the increase of rolling percentage, the grain size decreases and the mechanical properties improve.The effects of rolling on the texture of alloy show that, in the rolling process of Mg-8.5Li-1Al-1Ce alloys, besides the basal slip system, the prism and pyramidal slip systems are also activated inα(Mg) phase. Inβ(Li) phase, all the slip systems are evenly activated.The deformation behavior of Mg-5.5Li-3.0Al-1.2Zn-1.0Ce alloys shows that, when the extrusion temperature reaches 523K, the dynamic recrystallization takes place, and the fine equiaxed grains. After the extrusion plus rolling processes, many twin grains are found in microstructure. After the extrusion, the mechanical properties, including UTS, YS and elongation, of alloy are improved.Effects of deformation methods on the texture of Mg-5.5Li-3.0Al-1.2Zn-1.0Ce alloy were also researched. The results show that fibre texture exists in alloys after extrusion, and the basal face distributes preferrentially parallelling to extrusion direction. The prismatic plane (10(1|-)0) and the pyramidal plane (10(1|-)1) is equal to the extrusion direction. The deformation includes the prismatic slipping, pyramidal slipping and basal slipping. The extrusion plus rolling deformation process causes the more obvious (0002) basal face texture in alloys, and the deformation modes are mainly basal slipping and twinning.Y elements in Mg-8.5Li-3Al alloys bring about the refinement and spheroidization ofα(Mg) phase, and the intermetallics containing Y distribute evenly in the form of granular. The suitable Y content in Mg-Li-Al alloy has the effects of solid-solution strenghen, refinement strenghen and the second-phase strenghen. Sn has also the effects of refinement and spheroidization on theα(Mg) phase, and it is favorable for the dynamic recrystallization in the process of extrusion. Sn exists in the form of granular Mg₂Sn in Mg-Li-Al alloy at theα(Mg) boundary and in theβ(Li) phase. Mg₂Sn particles have the effects of refinement strength and second-phase strength.Then the aging behavior of Mg-Li-Al-Ce alloy was investigated. The results show that Ce content has obvious effects on the age-harden extension and aging dynamics. With the increase of Ce content, the aging hardness increases and the extention of over-aging soften decreases. During the aging process, MgLi₂Al is the age-harden phase. Phase transfermation and the decrease of amount of MgLi₂Al are the causes of over-age soften. Ce can hinder the over-age process in Mg-Li-Al alloys.Finally, the effects of Ce on the corrosion electrochemical behavior of Mg-8.5Li-3Al alloy were researched. Suitable Ce content improves the corrosion resistant property of Mg-8.5Li-3Al alloy. Ce can refine the microstructure of alloys and make the elements in alloys distribute evenly, and this causes the improvement of microstructure electrochemical uniformity. The mechanism of the electrochemical corrosion of Mg-Li alloys is different from other magnesium alloys. In Mg-Li alloys, the electrochemical corrosion mainly exists in the anode reaction.