等通道球形转角挤压过程中工业纯铝的微观组织演变与力学性能

Microstructure Evolution and Mechanical Properties of Commercially Pure Aluminum during the process of Equal Channel Angular Extrusion with Spherical Cavity(ECAE-SC)

摘要:

突破传统ECAP变形全过程通道等截面思路，提出一种耦合剪切应变和正应变于一体的新型等通道球形转角挤压（Equal channel angular extrusion with spherical cavity，ECAE-SC）工艺。在自行研制的模具上对工业纯铝进行室温单道次ECAE-SC挤压实验，采用OM、EBSD和TEM等技术手段，研究了ECAE-SC变形过程中工业纯铝微观组织的演变规律，并测试了变形后试样的显微硬度。结果表明，在ECAE-SC工艺剧烈简单剪切变形诱导下，工业纯铝仅需1道次挤压变形即可获得等轴、细小、均匀的超细晶组织，平均晶粒尺寸约为400 nm；工业纯铝室温ECAE-SC变形以位错滑移为主并伴有不完全连续动态再结晶，其微观组织经历了剪切带→位错胞→小角度亚晶→大角度等轴晶粒这一动态演化过程。1道次ECAE-SC变形后，工业纯铝组织以{110}<001>高斯织构为主，同时存在部分{111}<112>铜型织构；材料显微硬度值大幅提升，由初始28.94 HV提高到56.53 HV，增幅高达95.33%，且分布均匀性良好。

Abstract:

A new process named equal channel angular extrusion with spherical cavity (ECAE-SC) is proposed based on the idea of breaking through the equal channel during the whole process of traditional ECAP, which combines positive strain with shear strain. On the self-designed ECAE-SC die, the continuous, efficient and compound severe plastic deformation of commercially pure aluminum was realized in a single pass of ECAE-SC at room temperature. Microstructure evolution of commercially pure aluminum during ECAE-SC process was observed and analyzed by optical microscopy (OM), EBSD and TEM. Moreover, microhardness of the processed materials at different deformation regions was tested. The results show that under the severe plastic deformation induced by simple shear, the equiaxed ultrafine grains with average grain size of 400 nm can be obtained by only one pass of ECAE-SC. The deformation mechanism of ECAE-SC at room temperature is dominated by dislocation slip accompanied with incomplete continuous dynamic recrystallization, and the grain refinement process mainly includes the generation of shear bands, the formation of cellular substructures, the appearance of subgrains with low angle boundaries (LABs) and the formation of equiaxed ultrafine grains with large angle boundaries (HABs). After one pass of ECAE-SC, the main texture of commercially pure aluminum is Gauss texture {110} < 001 >, while some {111} < 112 > copper texture exists. The microhardness of the processed materials on the cross section increases significantly, and the average value increases from 28.94 HV to 56.53 HV, with an increase of 95.33%. Meanwhile, a more uniform hardness distribution is obtained.