Abnormally enhanced diamagnetism of Al-Zn-Mg alloys

We measured temperature and time dependences of magnetization of Al-1.0%Zn-4.2%Mg (ZM14), Al-2.6%Zn-3.2%Mg (ZM33), and Al-4.1%Zn-1.1%Mg (ZM41) (at.%) alloys after various periods of natural aging and peak-aged heat treatments. Abnormally enhanced diamagnetic contributions on the magnetization were observed for the as-quenched Al-Zn-Mg alloys for the first time. The enhanced diamagnetism observed in ZM33 and ZM41 were found to largely alter in natural aging, while that of ZM14 little changed. Since zero-field muSR is quite sensitive to the local magnetism, we would like to study electronic structure (local diamagnetism) of Zn-vacancy pairs/Zn-Mg-vacancy clusters. The results provide important information for industry to understand the complex precipitation phenomena of Al-Zn-Mg alloys and thus improve mechanical properties.

本研究测定了Al-1.0%Zn-4.2%Mg（ZM14）、Al-2.6%Zn-3.2%Mg（ZM33）及Al-4.1%Zn-1.1%Mg（ZM41）三种原子百分比（at.%）合金在不同自然时效时长与峰时效热处理后的磁化强度随温度与时间的变化关系。本研究首次在淬火态Al-Zn-Mg合金中观测到其磁化强度出现异常增强的抗磁贡献。研究发现，ZM33与ZM41中观测到的增强抗磁性在自然时效过程中会发生显著改变，而ZM14的增强抗磁性则几乎无变化。鉴于零场μ子自旋弛豫（zero-field muSR）对局部磁性具有极高敏感性，本研究拟探究Zn-空位对/Zn-Mg-空位团簇的电子结构（局部抗磁性）。上述研究结果可为工业界深入理解Al-Zn-Mg合金复杂的析出现象提供关键信息，进而助力其力学性能的优化与提升。