(1. 蘭州理工大學 省部共建有色金屬先進加工與再利用國家重點實驗室，蘭州 730050；
2. 蘭州理工大學 有色金屬合金及加工教育部重點實驗室，蘭州 730050)
摘 要: 利用光鏡(OM)、掃描電鏡(SEM)、X射線衍射儀(XRD)研究了Mg-6Zn-3Al-xMn(x%=0%, 0.1%, 0.3%, 0.5%，質量分數(shù))合金的鑄態(tài)組織和在等溫熱處理過程中的非枝晶組織演變規(guī)律。結果表明：鑄態(tài)基體合金由α-Mg、Mg2Zn3、Mg7Zn3和Mg32(Al, Zn)49)相組成。添加Mn后，析出了AlMn和Al8Mn5相，且隨Mn含量的增加，晶粒逐漸得到細化。合金經580 ℃等溫保溫30 min后，獲得的非枝晶組織由初生α1-Mg顆粒和包裹在共晶組織中二次水淬凝固形成的α2-Mg顆粒及分布在初生顆粒間呈蜂窩狀的共晶相組成。隨著Mn含量增加，固相顆粒的平均尺寸和形狀因子呈先減小后增加的趨勢，組織中液相比例逐漸減少。當Mn含量(質量分數(shù))為0.1%時，可獲得近似球狀、細小圓整、均勻分布的固相顆粒。在等溫熱處理過程中，溶質擴散和界面張力對組織演變起主導作用。Zn和Al溶質原子在液相中的成分起伏是初生顆粒在分離和球化過程中產生頸縮的重要原因。
關鍵字: Mg-6Zn-3Al合金；Mn含量；等溫熱處理；組織演變；頸縮
（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
