ECAP变形对Mg_2Si增强耐热镁合金组织及性能的影响

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

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.

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 the α-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 ~ 10 μm and tends to be well-distributed after 4-pass ECAP.The Mg2 Si 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 by19%. With increasing the ECAP passes,the high temperature creep resistance of the alloy is improved. The steadystate 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.