Combined-extrusion techniques for fabricating yield-symmetric ZK61 magnesium alloys rods focusing on texture influence on their mechanical responses

摘要

Three combined-extrusion techniques of second extrusion, die upsetting and extrusion, and cyclic extrusion and compression were used to fabricate three typical {0002} basal textures of fiber texture, dispersed texture and inclined texture, respectively, in the fine-grained ZK61 magnesium alloy. The tension-compression asymmetries were compared and the texture influence on asymmetry mechanical response was well evaluated using a Sem-ianalytical Sachs model that followed Schmid law and highlighted the importance of slip/twining activity in tension-compression asymmetry. It was found that in strong fiber-textured materials, solely refining grains could not obviously improve the tension-compression asymmetry. However, basal texture dispersed/inclined was conducive to activation of basal slip in tension and impeding of twining in compression, leading to gentler strain hardening and low tension-compression asymmetry. The uniaxial symmetry managed to be kept in cyclic loading under low strain amplitude, with the cyclic maximum stresses in accordance with uniaxial yield values. Sym-metric high-strength ZK61 magnesium alloys with tensile and compressive yield stresses (1.0 % offset) over 300 MPa were achieved by basal texture dispersion feasibly controlled by die upsetting extrusion technique.