Research On Microstructure And Mechanical Properties Of Mg-Li-Al-Mn Alloy

Mg-Li alloy is a large category of magnesium alloys,which has the advantages of good plasticity,but also has disadvantages such as insufficient strength of ordinary Mg-Li alloys.At the same time,there are also weaknesses such as the strength of ordinary Mg-Li alloys are not high enough.This article focuses on the related research on improving the properties of Mg-Li alloys through alloying and extrusion deformation,including the design and preparation of single-phase Mg-4Li-3Al-x Mn（x=0,0.3,0.5）and dual-phase Mg-8Li-1Mn-x Al（x=0,1）alloy,the alloy sample is extruded,and the microstructure of the alloy is characterized and analyzed by a metallurgical microscope,a scanning electron microscope（equipped with an EBSD probe）,etc.,testing and analyzing the tensile properties of the alloy at room temperature,and exploring the composition-process-Organization-Performance internal connection etc.The specific work and research results are as follows:（1）The Mg-4Li-3Al-x Mn（x=0,0.3,0.5）alloy was prepared by the melting method and annealed at 250℃*4h to obtain the as-cast alloy samples and study the microstructure and properties.The results show that the phase composition of the as-cast Mg-4Li-3Al alloy mainly consists ofα-Mg and Li Mg Al₂.With the addition of trace Mn elements,Al₈Mn₅ phase appears in the alloy,and the second phase is mainly distributed on the grain boundary;Mg-4Li-The tensile strengths of 3Al,Mg-4Li-3Al-0.3Mn,and Mg-4Li-3Al-0.5Mn alloys are 178MPa,139MPa and 155MPa,respectively,and the elongations are 8.8%,5.9%and 5.7%,respectively.There are some coarse precipitated phase particles in the room temperature tensile fracture morphology of adding trace Mn element.During the stretching process,these coarse precipitated phase particles cause stress concentration and become the source of cracks,which is not conducive to improving the plasticity and strength of the alloy.（2）The extruded samples of Mg-4Li-3Al-x Mn（x=0,0.3,0.5）alloy were prepared by hot extrusion process（extrusion temperature:300℃,extrusion ratio:25:1）,and the microstructure was studied.performance.The results show that the alloy grain size is significantly reduced after extrusion;the average grain size of the extruded Mg-4Li-3Al,Mg-4Li-3Al-0.3Mn,and Mg-4Li-3Al-0.5Mn alloys are 12.2μm,respectively,2.8μm and 3.6μm;the three alloys formed a typical magnesium alloy extrusion texture after hot extrusion,with the base plane parallel to the ED direction;among the three extruded alloys,Mg-4Li-3Al-0.3Mn alloy The mechanical properties are the best,with a tensile strength of 331MPa and an elongation of 16.1%.The main reason is that the fine-grain strengthening plays the most important role,and the second is that there is an unrecrystallized area（～27.12%）in the microstructure of the alloy during the hot extrusion process,and the grain basal plane（0001）of this area is parallel.In the ED direction,when the room temperature stretch is carried out along the ED direction,the Schmidt factor of the base slip（0001）<11-20>is almost equal to 0,and the slip is difficult to start.（3）The Mg-8Li-1Mn-x Al（x=0,1）alloy was prepared by the smelting method and annealed at 250℃*4h to obtain the as-cast alloy samples,and then subjected to the hot extrusion process（extrusion temperature:260℃）,Extrusion ratio:25:1).The Mg-8Li-1Mn alloy is mainly composed ofα-Mg,β-Li and Mn particles.By adding Al to the alloy,two second phases,Al₈Mn₅ and Li Mg Al₂,appear in the alloy.The tensile strengths of Mg-8Li-1Mn and Mg-8Li-1Mn-1Al alloys are 156MPa and 199MPa,respectively,and the elongation is 19.2%and 11.3%respectively.The tensile strength of the extruded Mg-8Li-1Mn-1Al alloy containing Al is 43MPa higher than that of the extruded Mg-8Li-1Mn alloy,mainly due to the strengthening effect of the second phase particles.（4）The extruded samples of Mg-8Li-1Mn-1Al alloy were prepared by hot extrusion process（extrusion temperature:260℃,220℃,extrusion ratio:25:1）.The tensile strength of the Mg-8Li-1Mn-1Al alloy extruded at 260℃and 220℃is 199MPa and 219MPa,and the elongation rate is 11.3%and 9.0%,respectively.The tensile strength of the alloy when the extrusion temperature is 220°C is 20MPa higher than that when it is extruded at 260°C,and the elongation does not decrease significantly.The main reason is that work hardening during the low temperature extrusion process is more conducive to improving the strength of the alloy.