电场辅助镁锂合金超塑变形行为及其在微型热管成形中的应用

Electric field assisted superplastic deformation behavior of Mg⁃Li alloy and its application in micro heat pipe forming

通过等通道转角挤压工艺制备了不同晶粒尺寸的LZ91镁锂合金,当挤压道次超过8道次后,晶粒尺寸基本不再细化。为了探究电场作用下LZ91镁锂合金的超塑变形行为,设计并制造了电场辅助超塑单向拉伸实验平台,提出了一种“递减式”恒压通电方案,开展了不同电压、初始应变速率和晶粒尺寸下的电场辅助单向拉伸实验。实验结果表明,随着电压的增大,电流的焦耳热效应增大,LZ91镁锂合金的真应力-真应变曲线逐渐呈现出稳态流变特征。所有电压下原始镁锂合金的伸长率差异不明显,最大差异仅为16%。相比于低电压时,在高电压下初始应变速率对LZ91镁锂合金超塑变形行为的影响更加显著。电场对细晶LZ91镁锂合金超塑变形行为影响较大,主要体现在降低超塑变形温度和提高伸长率。在获得电场作用下LZ91镁锂合金超塑性能的基础上,通过DEFORM-3D仿真软件对LZ91镁锂合金微型热管挤压成形工艺进行了设计与仿真,长度为5 mm的坯料仿真得到的微型热管长度为40 mm,微沟槽深度为0.25 mm,等效应变分布均匀,为微型热管电场辅助成形工艺提供了有益探索。

LZ91 Mg⁃Li alloys with different grain sizes were prepared by equal channel angular extrusion process.When the extrusion passes exceeded 8 passes,the grain size was basically no longer refined.In order to investigate the superplastic deformation behavior of LZ91 Mg⁃Li alloy under the action of electric field,an electric field assisted superplastic uniaxial tensile experiment platform was designed and manufactured.A“decreasing”constant voltage electrification scheme was proposed,and electric field assisted uniaxial tensile experi⁃ments were carried out under different voltages,initial strain rates and grain sizes.The experimental results show that as the voltage in⁃creases,the Joule heating effect of the current increases,and the true stress⁃true strain curves of LZ91 Mg⁃Li alloy gradually present steady state rheological characteristic.The difference in elongation of initial Mg⁃Li alloy at all voltages is not obvious,with the maximum difference of only 16%.Compared with low voltage,the effect of initial strain rate on the superplastic deformation behavior of LZ91 Mg⁃Li alloy is more significant at high voltage.The electric field has a great influence on the superplastic deformation behavior of the fine⁃grained LZ91 Mg⁃Li alloy,which is mainly reflected in reducing the superplastic deformation temperature and increasing the elongation.On the basis of obtaining the superplastic properties of LZ91 Mg⁃Li alloy under the action of electric field,the extrusion forming process of LZ91 Mg⁃Li alloy micro heat pipe was designed and simulated by DEFORM⁃3D simulation software.The length of the micro heat pipe obtained by simulating the billet with length of 5 mm is 40 mm,the microghole depth is 0.25 mm,and the effective strain distribution is uniform,which provides beneficial exploration for electric field assisted forming process of micro heat pipe.