工业纯铝等通道球形转角挤压数值模拟与实验研究

Numerical simulation and experimental investigation of commercially pure aluminum during equal channel angular extrusion with spherical cavity

为提高传统ECAE工艺的挤压效率和变形效果,提出一种具有“球形分流”结构的新型等通道球形转角挤压工艺。采用DEFORM-3D有限元软件对工业纯铝ECAE-SC变形过程进行模拟,研究金属流动、挤压载荷、等效应变以及平均应力的分布及变化规律;在自行设计的ECAE-SC模具上成功实现工业纯铝室温单道次连续变形,对变形组织进行了EBSD分析和显微硬度测试。结果表明:ECAE-SC模具外角处球状圆弧的平滑过渡有效改善底部金属流动性,坯料经球形转角依次发生剪切、膨胀和挤压等3种不同形式的复合变形,挤压载荷表现出“急剧上升缓慢增加稳定变形”的变化趋势;1道次ECAE-SC变形后,坯料内部平均累积塑性应变高达3.07,沿长度方向形成1个近似平行四边形的稳定应变区,变形均匀性良好;工业纯铝坯料经室温1道次ECAE-SC变形后,外形完整、表面光滑、宏观无裂纹;材料内部形成大量细长的剪切变形带,晶粒破碎和细化现象明显,平均显微硬度大幅提高,由初始36.6HV增加至58.7HV。

In order to improve the extrusion efficiency and deformation quality of traditional ECAE process,a novel technique named equal channel angle extrusion with spherical cavity (ECAE-SC) was proposed,which has the characteristics of “spherical split-flow”.The finite element simulation of commercially pure aluminum during ECAE-SC process was carried out using DEFORM-3D software.The variation and distribution of metal flow,extrusion load,equivalent strain and mean stress during ECAE-SC process were investigated.Moreover,commercially pure aluminum was successfully processed after 1 pass of ECAE-SC at room temperature on the self-designed die with continuous deformation.The electron back scattered diffraction (EBSD) was used to evaluate the microstructure of commercially pure aluminum,and microhardness tests were conducted for the processed billet.The results show that the smooth transition of spherical arc on the outer corner of ECAE-SC die can effectively improve the metal flow at the bottom.During ECAE-SC process,the billet undergoes shear,expansion and extrusion with continuous deformation when it passes through the spherical corner,the load presents a characteristic of “sharp increase - slow increase - steady deformation”.The average equivalent strain reaches up to 3.07 after a single pass of ECAE-SC,a stable strain region approximately to a parallelogram forms along the length direction,with a reasonable level of strain uniformity.After 1 pass of ECAE-SC,the extruded billet is free of macro crack with intact shape and good surface quality,lots of shear bands are generated leading to the significant grain refinement and fragmentation.The average value of microhardness is drastically increased from 36.6 HV to 58.7 HV.