镁合金逆温度场等径角挤压的有限元模拟与实验分析

Finite Element Simulation and Experimental Analysis of Mg Alloy Processed by Inverse Temperature Field Equal Channel Angular Pressing

摘要:

为揭示模具温度对逆温度场等径角挤压（inverse temperature field-equal channel angular pressing，ITF-ECAP）加工镁合金坯料温度场与等效应力场的影响规律，建立了Mg-1.5Bi(wt%，B2)合金ITF-ECAP加工过程的热力耦合有限元分析模型，并结合实验研究对其在不同模具温度下的加工过程进行分析。结果表明：ITF-ECAP加工过程中坯料温度在模具通道转角处显著升高，有助于塑性变形的顺利进行，剧烈变形后温度逐步降低，可有效避免再结晶晶粒的粗化；坯料的应力集中区域主要分布在通道转角处与模具出口附近，且随着模具温度的升高而显著降低。验证实验发现在模具温度较低（200 ℃）时，一道次ITF-ECAP加工后B2合金坯料表面发生开裂，而模具温度为300 ℃时，B2合金经过四道次ITF-ECAP加工后表面光滑无裂纹。进一步微观组织表征发现，四道次ITF-ECAP加工的B2合金中形成了由细晶与超细晶构成的超-细混晶组织，显著提升了合金的强度与塑性。

Abstract:

To investigate the influence of mold temperature on the temperature field and equivalent stress field of Mg alloy processed by inverse temperature field equal channel angular pressing (ITF-ECAP), a thermal mechanical coupled finite element analysis model was established for ITF-ECAP processing of B2 alloy (Mg-1.5Bi, wt%). Combined with experimental research, the processing process of B2 alloy at different mold temperatures was analyzed. The results show that during the ITF-ECAP, the temperature of the billet significantly increases at the corner of the mold channel, which facilitates smooth plastic deformation. After severe deformation, the temperature gradually decreases, thereby inhibiting coarsening of recrystallized grains. The stress concentration of the billet mainly occurs at the corner of the channel and near the mold outlet, and it significantly decreases with the increase in mold temperature. The experiment verification finds that when the mold temperature is low (200 ℃), the surface cracking of B2 alloy billet occurs after one-pass ITF-ECAP processing. In contrast, the surface of B2 alloy can be ITF-ECAP processed for four passes without surface cracking when the mold temperature is set as 300 ℃. Further microstructural characterization reveals that a bimodal grain structure composed of fine and ultrafine grains is formed after four-pass ITF-ECAP deformation, leading to a simultaneous improvement in both strength and ductility.