LZ91镁锂合金板材的超塑性气胀成形研究

Study on Superplastic Gas Bulging Forming of LZ91 Mg-Li alloy sheet

摘要:

本文利用热拉伸实验、气胀成形实验、金相分析和扫描电镜观察，研究LZ91镁锂合金板材的超塑性、气胀成形性能及其组织结构。结果表明:在热拉伸变形温度为573 K、应变速率为0.001 s-1时，其伸长率可达343.7 %，应变速率敏感指数为0.697，轧制态的LZ91合金板材表现出优良的超塑性；在胀形温度573 K，胀形气压0.06 MPa条件下，板材成形高度为51.14 mm，高径比达1.279，说明该镁锂合金板材具有良好的超塑性成形潜力；在热拉伸变形和超塑性气胀成形过程中，均有动态再结晶现象产生，可有效提高该合金的塑性成形能力；在拉伸断口和胀形件破裂处断口均存在典型的超塑性空洞形貌特征，说明两者的主要变形机制均为晶界滑移，且合金超塑性失效的主要原因是空洞的长大和连接。

Abstract:

The superplasticity, gas bulging forming properties and microstructure of LZ91 Mg-Li alloy sheet were studied by hot tensile test, gas bulging forming experiment, metallographic analysis and scanning electron microscope observation. The results show that the rolled LZ91 alloy sheet exhibits excellent superplasticity: the elongation is up to 343.7% and the strain rate sensitivity index is 0.697 when the hot tensile temperature is 573 K and the strain rate is 0.001 s-1. Under the conditions of bulging temperature of 573 K and bulging pressure of 0.06 MPa, the sheet forming height is 51.14 mm and the height-diameter ratio is 1.279, which indicates that the Mg-Li alloy sheet has good superplastic forming potential. Dynamic recrystallization occurs in both hot tensile and superplastic gas bulging forming, it can effectively improve the plastic forming ability of the alloy. The typical superplastic cavities morphology at both tensile fracture and bulging fracture shows that the main deformation mechanism is grain boundary slip, and the main cause of superplastic failure is the growth and connection of the cavity.