Study On Structure, Properties And Heat Treatment Process Of Extruded Magnesium-Lithium Alloy

This paper designs Mg-9Li-0.2Zn-0.2Si and Mg-12Li-2Al-2Zn-0.8RE two newmultivariate Mg-Li alloys, basing on the study of microstructure and properties ofthese two cast alloy, the paper has a further study on the effect of hot extrusion andheat treatment on the microstructure and properties in order to improve themechanical properties of Mg-Li alloy by plastic deformation and heat treatmentprocess.The results showed that: Mg-9Li-0.2Zn-0.2Si cast alloy is mainly composed ofβ-Li, α-Mg and polygonal precipitates Mg2Si,Mg-12Li-2Al-2Zn-0.8RE cast alloy ismainly composed of β-Li, Al0.9Li34.3Mg64.5Zn0.3, Al2Ce and AlCe four phase whereβ-Li as the matrix phase. After hot extrusion, dynamic recrystallization occurs in thematrix phase β-Li in Mg-9Li-0.2Zn-0.2Si alloy and show as uniformly distributedfine equiaxed grains, α-Mg is unevenly stretched in the extrusion direction, and castprecipitation phases are distributed in the grain boundary phase in the extrusiondirection. The strength increases from94.4MPa of the cast alloy to114.6MPa, Duringextrusion process, in Mg-12Li-2Al-2Zn-0.8RE alloy dynamic recrystallization occurson the β-phase forming equiaxed grain, dynamic recrystallization of β-Li makes castprecipitates at the grain boundaries more evenly distributed, while extrusion promotesthe precipitation of new phase MgZn; The tensile strength of the extruded alloyincreases from the cast alloy’s142.7MPa to178.1MPa.While Mg-9Li-0.2Zn-0.2Si is undergoing the process of370℃×6h solidsolution+150℃×8h aging treatment, precipitates disperses in the β-phase matrixafter the alloy has been aging for8h and hardness along peaks; The optimum agingtime for the alloy is150℃×8h. When soluting at380℃,AlCe and MgZn phasespresentes in the extruded are almost completely solid soluted, and the correspondingalloy reaches the highest hardness. During380×6h solution+150℃×16h treatmentAlCe phase re-precipitate and the alloy precipitate a new phase Mg12Ce; when aging32h the new phase AlLi precipitates; The hardness of corresponding alloyfluctuates,it increases first and then reduces. When aging for16h, the hardness of the alloy peaks at71.2HBW. By undergoing extruding and380×6h solid solution+150℃×16h aging process, the tensile strength and elongation of Mg-12Li-2Al-2Zn-0.8RE alloy respectively reaches206.5Mpa and34.6%, which are improved by45%and180%compared with the cast and has good mechanical properties.