采用光学显微镜(OM),场发射扫描电镜(SEM),透射电镜(TEM),X射线衍射分析(XRD)和高温拉伸试验等研究了稀土Nd元素对ECAP态Mg-15Al合金显微组织及高温力学性能的影响.实验结果表明:随着Nd含量的增加,Mg-15Al-xNd合金平均晶粒尺寸逐渐减小,当Nd含量达到1.5％和4％时,组织中分别出现针状Al11Nd3和不规则块状Al2Nd相.经ECAP挤压四道次后,基体平均晶粒尺寸2～3 μm,β-Mg17Al12相显著细化且呈弥散分布状态.稀土Nd元素可以有效改善ECAP态Mg-15Al合金的高温力学性能,当Nd含量为1.5％时,合金在200℃时的屈服强度和抗拉强度由未加Nd时的116 MPa和139 MPa分别提高到148 MPa和172 MPa.ECAP挤压过程中被碎化的高熔点Al-Nd相在高温下对晶界有较强的钉扎作用,表现出显著的细晶强化和弥散强化效果.
The effects of rare earth element Nd on microstructure and elevated temperature mechanical properties of ECAPed Mg-15Al-xNd alloys were studied by means of optical microscope (OM),field emission scanning electron microscopy (SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD) and tensile testing at elevated temperature.The results indicate that the average grain size of the Mg-15Al-xNd alloys decreases with the addition of Nd,and needle-like Al11Nd3 phases and irregular shaped Al2Nd phases appear when Nd content reaches 1.5％ and 4％,respectively.After ECAP for four passes,the average grain size is reduced to about 2-3 μm and the β-Mg17Al12 phase is significantly refined.The elevated temperature mechanical properties of the ECAPed Mg-15Al-xNd alloys can be improved effectively with the addition of Nd.When tensile testing at 200 ℃,the yield strength and ultimate tensile strength of the ECAPed Mg-15Al alloy are 116 MPa and 139 MPa,however,the values are increased to 148 MPa and 172 MPa for the ECAPed Mg-15Al-1.5Nd alloy,respectively.The grain refinement strengthening and dispersion strengthening are main mechanisms for the improvement of the properties of the Mg-15Al-l.5Nd alloy after the ECAP processing which benefits from the pinning effect of the refined dystectic Al-Nd phases on grain boundaries.
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