ECAP变形对Mg2Si增强耐热镁合金组织及性能的影响

为了提高镁合金的耐热性能,在Mg-Zn合金中加入Si,形成Mg-Zn-Si镁合金.采用ECAP工艺在变形温度为573 K和挤压路径为Bc条件下对Mg-Zn-Si镁合金进行不同道次的变形.运用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段对变形后的Mg-Zn-Si镁合金进行了组织表征,对变形后的合金进行了室温拉伸和高温蠕变等力学性能测试.结果表明:随着挤压道次增加,α-Mg基体、Mg Zn相及Mg2Si相均得到细化且分布趋于均匀.1道次挤压后部分基体α-Mg细化,4道次挤压后α-Mg的尺寸减小为5~10μm,且晶粒大小趋于均匀;2道次挤压后Mg2Si相枝晶在原位置破碎为颗粒状,6、8道次挤压后Mg_2Si相呈弥散分布.4道次挤压后合金的屈服强度和抗拉强度均提高120%,伸长率提高353%;8道次挤压后合金的抗拉强度和伸长率与4道次相比变化不大,但屈服强度进一步提高了19%.随着挤压道次增加,高温抗蠕变性能提高,8道次后高温稳态蠕变速率降低5倍.Mg2Si相细化机理为受剪切而机械碎断.

Effect of ECAP on microstructure and properties of Mg-Zn-Si heat-resistant magnesium alloy

In order to improve the heat resistance of magnesium alloy, Si is added to the Mg-Zn alloy to form Mg-Zn-Si magnesium alloy. The ECAP deformation of Mg-Zn-Si magnesium alloy was carried out under different conditions of deformation temperature of 573 K and extrusion path of Bc. The microstructure of the ECAPed Mg-Zn-Si magnesium alloy was examined by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy ( SEM) and transmission electron microscopy ( TEM) . The mechanical properties of the ECAPed alloys were detected by room temperature tensile and high temperature creep tests. Results show that all the average sizes of theα-Mg phase, Mg-Zn phase and Mg2 Si phase are reduced and their distribution become uniform with increasing the extrusion passes. After 1-pass ECAP, part of the α-Mg matrix is refined. The grain size of the α-Mg phase is decreased to 5~10μm and tends to be well-distributed after 4-pass ECAP . The Mg2Si dendrites are crushed into granular shape after 2 pass ECAP, and dispersed after 6 and 8 pass ECAP. The yield strength and the ultimate tensile strength of the 4 pass ECAPed alloy increase by 120%, and its elongation increases by 353%; Compared with the 4 pass ECAPed alloy, the ultimate tensile strength and the elongation of the 8 pass ECAPed alloy almost remain unchanged, whereas its yield strength further increase by 19%. With increasing the ECAP passes, the high temperature creep resistance of the alloy is improved. The steady-state creep rate at high temperature of the 8 pass ECAP sample is 5 times lower than that of the as-cast sample. The refinement of Mg2Si phases can be attributed to the mechanical crushing induced by shear deformation.