Mg-Zn基合金中非周期性析出相的原子尺度

Atomic-scale investigation of the aperiodic precipitates in the Mg-Zn based alloys

时效析出相的结构是主导合金强度提升的关键,因此从原子尺度认识析出相的结构出发,有助于更好地设计新合金.使用球差校正的高角环形暗场扫描透射电镜(HAADF-STEM)结合选区电子衍射(SAED)技术系统表征了峰时效Mg-Zn(-Al)系合金中的非周期性析出相结构.研究结果表明,Mg-8Zn二元合金等温时效析出的棒状相是由72°菱形和72°等边六边形结构单元在(0001)α面上沿5个方向拼砌形成的,具有带Laves晶体特征的纳米畴结构.Al的添加可以显著改变Mg-Zn合金的时效析出行为,Mg-8Zn-4Al合金中析出了两种非周期性结构:一种是由36°菱形、72°菱形和72°等边六边形等结构单元自适应组装形成的块状析出相,其伪10次轴完全平行于[0001]α方向;还有一种是菱形的三维二十面体准晶相,其5次轴完全平行于[0001]α方向.这些原子尺度的相结构信息不仅可以增进人们对凝聚态物质结构的认识,还可为设计高强度的ZK,AZ系列镁合金提供理论依据.

The atomic configuration of aging precipitates is the key to improving the strength of alloys,and understanding the atomic structural details of precipitates would help to better design high-strength alloys.Here,the atomic configurations of aperiodic precipitates in peak-aged Mg-Zn(-Al)series alloys are systematically investigated employing aberration-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)combined with selected area electron diffraction(SAED)techniques.The results show that the rod-like phase precipitated by isothermal aging in the Mg-8Zn binary alloy are multidomain structures with Laves characteristics,which are assembled by the 72°rhombus structures and 72°equilateral hexagon structures in the(0001)_αbasal plane.Additionally,it is found that the aging precipitation behaviors of the Mg-8Zn alloy can be significantly altered with the addition of Al,and two kinds of aperiodic precipitates formed in the Mg-8Zn-4Al binary alloy have thus been confirmed.One is a bulk precipitate phase formed by the self-adaptive assembly of structural units assembled by 36°rhombus,72°rhombus,and 72°equilateral hexagon,whose pseudo 10-fold axes are fully parallel to the[0001]_αzone axis.Another one is also a rhombus-shaped three-dimensional icosahedral quasicrystal phase,whose 5-fold axis is completely parallel to the[0001]_α.This atomistic information of aperiodic precipitates in the Mg-Zn(-Al)series alloys not only leads to new insights into the structure and formation mechanism in the condensed matters but also provides theoretical guidance for the design of high-strength ZK and AZ series Mg alloys.