微量Er在高强Al-Zn-Mg-Cu合金中的存在形式及其“遗传效应”

Existence Form of Trace Er in Al-Zn-Mg-Cu Alloy and Its "Genetic Effect"

采用铁模铸造制备Al-Zn-Mg-Cu及Al-Zn-Mg-Cu-0.15%Er两种合金铸锭。利用光学显微镜(OM)、扫描电镜(SEM)及能谱分析(EDS)、差热分析(DSC)、透射电镜(TEM)、X射线衍射分析(XRD)和室温拉伸等方法研究了Er元素在Al-Zn-Mg-Cu合金铸态组织、均匀化态组织、变形组织以及时效态组织中的存在形式、作用机理以及其对合金室温拉伸性能的影响。结果表明:微量Er元素对Al-Zn-Mg-Cu合金铸态组织有一定细化作用,但这种作用较为有限。Er在合金中主要以三元Al8Cu4Er相的形式存在,该相在合金凝固过程中形成并偏聚在晶界附近,常出现在共晶网状结构之间。此外,还有少量的Er生成了细小Al3Er粒子。Al8Cu4Er相熔点约为573.8°C,为难溶硬脆第二相,在合金变形过程中易破碎从而会导致裂纹萌生或成为粒子诱发再结晶形核的核心,最终会对合金的综合力学性能产生不利的影响。

Two kinds of alloys Al-Zn-Mg-Cu and Al-Zn-Mg-Cu-0.15%Er were prepared by steel mould casting.The existence form of Er in the as-cast,homogenized,deformed and aged microstructures of the Al-Zn-Mg-Cu alloy were investigated by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),differential scanning calorimetry(DSC),transmission electron microscopy(TEM)and X-ray diffractometry(XRD).In addition,the effect of Er on the tensile properties of the alloy at room temperature was also discussed.The results show that trace element Er can refine the as-cast microstructure of Al-Zn-Mg-Cu alloy to a certain extent,but this refinement is limited.Er exists in the alloy mainly in the form of a ternary Al8Cu4 Er phase,which forms during the solidification and segregates at the grain boundaries,and which often occurs between eutectic networks.Al8Cu4 Er has a high melting point and poor plasticity and is therefore easily crushed during the thermal deformation of the alloy.Al8Cu4 Er fragments may cause cracks and may also induce recrystallization nucleation,which will eventually have an adverse effect on the comprehensive properties of the alloy.