(1. 兰州理工大学 省部共建有色金属先进加工与再利用国家重点实验室，兰州 730050；
2. 兰州理工大学 有色金属合金及加工教育部重点实验室，兰州 730050)
摘 要: 利用光镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)研究了Mg-6Zn-3Al-xMn(x%=0%, 0.1%, 0.3%, 0.5%，质量分数)合金的铸态组织和在等温热处理过程中的非枝晶组织演变规律。结果表明：铸态基体合金由α-Mg、Mg2Zn3、Mg7Zn3和Mg32(Al, Zn)49)相组成。添加Mn后，析出了AlMn和Al8Mn5相，且随Mn含量的增加，晶粒逐渐得到细化。合金经580 ℃等温保温30 min后，获得的非枝晶组织由初生α1-Mg颗粒和包裹在共晶组织中二次水淬凝固形成的α2-Mg颗粒及分布在初生颗粒间呈蜂窝状的共晶相组成。随着Mn含量增加，固相颗粒的平均尺寸和形状因子呈先减小后增加的趋势，组织中液相比例逐渐减少。当Mn含量(质量分数)为0.1%时，可获得近似球状、细小圆整、均匀分布的固相颗粒。在等温热处理过程中，溶质扩散和界面张力对组织演变起主导作用。Zn和Al溶质原子在液相中的成分起伏是初生颗粒在分离和球化过程中产生颈缩的重要原因。
关键字: Mg-6Zn-3Al合金；Mn含量；等温热处理；组织演变；颈缩
（1. State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Non-ferrous Metal Alloys and Processing, Ministry of Education, Lanzhou University of Technology, Lanzhou 730050, China）
Abstract:The as-cast microstructure and non-dendritic microstructure evolution of Mg-6Zn-3Al alloys with varied Mn content (0%, 0.1%, 0.3% and 0.5%, in mass fraction) under isothermal heat treatment process were investigated with an OM, SEM and XRD, respectively. The results indicate that the as-cast Mn-free alloy is composed of α-Mg, Mg2Zn3, Mg7Zn3 and Mg32(Al, Zn)49 phases. When the minor Mn is added to the based alloy after, resulting in the creation of AlMn and Al8Mn5 phases, meanwhile, the grains are gradually refined with the Mn content increasing. The alloys are isothermally treated at 580 ℃ for 30 min, the obtained non-dendritic microstructures are comprised of primary α1-Mg particles and α2-Mg particles existed in eutectic microstructures which form in secondary quenching solidification process as well as eutectic phases with alveolate morphologies distributed between the primary solid particles. With the increase of Mn content, the average size and shape factor of solid phase particles decrease first and then increase, the volume fraction of liquid phase decreases continuously. When the content of Mn is 0.1%, the similarly spherical, finer and roundness as well as uniform distribution solid phase particles are obtained. The solute diffusion and interfacial tension play a leading role in the microstructural evolution during isothermal heat treatment. The component fluctuation of Zn and Al solute atoms in liquid phase is an important reason for the generation of necking in the process of separation and spheroidization of primary particles.
Key words: Mg-6Zn-3Al alloy; Mn addition; isothermal heat treatment; microstructural evolution; necking
