孪晶种类对镁合金板材室温塑性性能的影响

菜单

摘要：变形镁合金以其优异的性能而倍受关注，但因室温塑性较低而限制了其在工业中的广泛应用。纯镁及镁合金为 HCP 结构，孪生是镁合金室温塑性变形中重要的变形方式。开展镁合金孪生变形的研究，对提高和改善镁合金塑性变形具有重要意义。本文主要研究了表面纹理轧制、弯曲轧制、异速比等工艺对AZ31镁合金板材孪晶及室温塑性的影响，并借助光学显微镜和万能试验机进行了显微组织和力学性能的分析，对比了AZ31镁合金轧材孪晶的种类、数量对室温力学性能的影响，由此分析孪生在塑性变形过程中的作用。主要研究内容和结果如下：

（1）通过表面纹理轧制，发现压下量对镁合金的孪晶和力学性能有明显的影响。对比两种压下量表面纹理轧制后的镁合金板材单向拉伸和金相试验，结果表明：AZ31镁合金在辊温差25℃时，采用大压下量的轧制方式所获得的轧制板材的延伸率最高为9.68%，屈服强度和抗拉强度分别为172MPa和270MPa。与小压下量的轧制方式获得轧件的性能相比较，其室温延伸率明显提高，孪晶的形态主要是拉伸孪晶并且有少量的压缩孪晶，而其他压下量的轧制方式得到的轧件的孪晶为拉伸孪晶，因此，压缩孪晶对于它对位错滑移有阻碍作用。42347

（2）通过弯曲轧制，发现不同弯曲方式对AZ31镁合金轧材的孪晶和力学性能有明显的影响。反复弯轧的延伸率为8.47%，屈服强度和抗拉强度分别为155MPa和295MPa，而弯轧+平轧延伸率达到15.6%，同时材料的抗拉强度达到330MPa。前者的孪晶的数量较少并且形态多为拉伸孪晶，而后者材料的上下表面处有少量细晶层，这是因为在晶界处和孪晶内晶粒细化所致，因此弯+平轧制工艺能明显提高镁合金的延伸率。

（3）通过异速比轧制，发现异速比对AZ31镁合金轧材的孪晶和力学性能有明显的影响。对比不同异速比发现异速比在1:1.25时能明显提高镁合金材料的延伸率且降低屈服强度，其延伸率为24.09%，屈服强度和抗拉强度分别为114MPa和275MPa，所得板材中孪晶比同步轧制中要少得多，主要为拉伸孪晶，这是因为异步轧制时滑移系更容易启动，孪生不容易发生，因此异步轧制能够在一定程度上改善镁合金的塑性变形能力。这对镁合金的应用范围的扩大，有着极其重要的意义。42347

由于轧制板材存在很大的应力因素，本文采用了多种方法也未能完成EBSD观察，希望在未来能够在此有所突破。

毕业论文关键词：镁合金；孪生；轧制

Effect of twinning kind of sheet plastic properties of magnesium alloys at room temperature

Abstract：wrought magnesium alloy for its outstanding performance and attracting much attention, but the low temperature ductility and limit its wide application in industry. Pure magnesium and magnesium alloy for the HCP structure, magnesium alloy twin room temperature plastic deformation important variant. Research magnesium alloy twin deformation, is important to enhance and improve the magnesium alloy plastic deformation. This paper studies the effects of surface texture of plastic rolling, rolling curved, iso-ratio and other technology for AZ31 magnesium alloy sheet twins and room temperature, and with an optical microscope and a universal testing machine analyzed the microstructure and mechanical properties, Compare the types of AZ31 magnesium alloy rolled twinning, the impact on the number of mechanical properties at room temperature, thereby analyze the role of twins in the plastic deformation process. The main contents and results are as follows:

(1) by rolling surface texture, we found a significant reduction on twinning and mechanical properties of magnesium alloys. Magnesium alloy sheet-way comparison of the two reduction rolling surface texture after stretching and metallurgical test results showed that: AZ31 magnesium alloy roll temperature difference 25 ℃, the use of large rolling reduction of rolling method obtained elongation sheet made up to 9.68%, the yield strength and tensile strength were 172MPa and 270MPa. And a small reduction in the rolling way to get rolling performance compared to significantly increase its elongation at room temperature, the main form of twinning is twinning and drawing a small amount of compression of twins and other reduction rolling twinning rolling way to get stretched twins, therefore, for its compression twins hinder dislocation slip effect.