Microstructures Evolution And Mechanical Properties Of 2A66 Aluminium-lithium Alloy Subjected To Repetitive Upsetting And Extrusion

Al-Li alloy is considered as one of the most potential structural materials for space and aerial applications, because of its low density, high specific strength, high specific stiffness, high elastic modulus and excellent fatigue resistance. Repetitive upsetting and extrusion was conducted on 2A66 Al-Li alloy in the present study. It aimed at refining the grains, homogenizing the microstructures, disintegrating the textures and improving the mechanical anisotropy of 2A66 Al-Li alloy to promote its applications in aerospace field. Optical microscopy (OM), electron back-scatter diffraction (EBSD), scan electron microscopy (SEM), transmission electron microscopy (TEM), hardness testing and room temperature tensile testing were performed to investigate the microstructure characteristics and mechanical properties of 2A66 Al-Li alloy subjected to different deformation rate and extracted from different region of the same sample (The effective strain for each RUE pass was 1.708). Additionally, the grain refinement mechanism and toughening mechanism were explored. The main conclusions were drawn as follow:The RUE processing was effectively refining the grains of 2A66 Al-Li alloy, following by high fraction of high angel grain boundaries (HAGBs). The average grain size was reduced from as-extruded?140?m to ?4?m after 3 RUE passes. The grains of the as-extruded 2A66 Al-Li alloy were mainly surrounded by low angel grain boundaries (LAGBs) below 5°. The fraction of HAGBs increased from as-extruded 47.28% to 86.37%8 after 3 RUE passes. The grain refinement mechanism of 2A66 Al-Li alloy during RUE processing was a compound mechanism of discontinuous dynamic recrystallization and continuous dynamic recrystallization. With increasing strains, the discontinuous dynamic recrystallization became weak.The RUE processing had great influence in the texture of 2A66 Al-Li alloy. The intensity of texture significantly reduced from 97.743 to 21.486 after 3 passes of RUE processing. The component of texture also changed after RUE processing. The dominant textures of as-extruded 2A66 Al-Li alloy were{112}<111>+{11O}<111> texture. After 3 RUE passes, the main textures were{001}<100>+{112}<111> texture.There was little difference in the grain morphology and grain size of 3 passes RUE processed 2A66 Al-Li alloy at different regions. The grains at surface were a little smaller than those at the center. The standard deviation of grain size reduced from original 4.81 to about 1 after 3 RUE passes. The difference of the textures was great. The textures at center were dominant by CubeRD texture//<001> orientation. The textures of the region (a 0.5r distance from the center) were dominant by cube texture and texture//<111> orientation. The textures at surface were dominant by shear texture //<011> orientation.The ductility was greatly improved with modest decrease in tensile strength and yield strength after RUE processing. The elongation to failure of as-extruded 2A66 Al-Li alloy was 18.2%. After 3 RUE passes, the elongation to failure increased to 34.2%. The modification of mechanical properties of 2A66 Al-Li alloy were the combined effect of dislocation, texture and the second phase. The reduction in strength was attributed to the modification of configuration and density of dislocation, the textures converting to favorable orientation, and the reduction of ?' phase. The improvement of ductility was attributed to the grain refinement, the modification of density and the fragment and redistribution of the second phases leading to more homogeneous deformation, the increase of HAGBs favoring to grain boundaries sliding.