半固態(tài)組織的形成
(1. 蘭州理工大學(xué) 甘肅省有色金屬新材料省部共建國家重點實驗室，蘭州 730050；
2. 蘭州理工大學(xué) 有色金屬合金省部共建教育部重點實驗室，蘭州 730050)
摘 要: 半固態(tài)漿料的固相顆粒尺寸、形態(tài)和分布主要取決于熔化過程中液相的形成與演化過程。采用添加0.5%富鈰混合稀土來改善AZ91D鎂合金的鑄態(tài)組織，研究在半固態(tài)等溫?zé)崽幚碇械慕M織演變以及非枝晶組織制備與控制的機理。結(jié)果表明：稀土合金化處理可促進初生相在等溫?zé)崽幚磉^程中由枝晶向粒狀晶的轉(zhuǎn)變，可獲得更加細(xì)小、均勻的球狀固相顆粒，并且其粗化速度較慢。半固態(tài)等溫?zé)崽幚磉^程中，整個系統(tǒng)處于熔化和結(jié)晶的動態(tài)平衡，鑄態(tài)組織中枝晶根部高溶質(zhì)濃度區(qū)或系統(tǒng)的溫度、濃度起伏是固相顆粒內(nèi)液相形成的內(nèi)在和外在條件。
關(guān)鍵字: 鎂合金；稀土；半固態(tài)；組織演變
semi-solid microstructural evolution of AZ91D alloy
（1. State Key Laboratory of Gansu Advanced Non-ferrous Metal Materials,
Lanzhou University of Technology, Lanzhou 730050, China;
2. Key Laboratory of Non-ferrous Metal Alloys, Ministry of Education,Lanzhou University of Technology, Lanzhou 730050, China）
Abstract:The size, shape and distribution of solid phase particle in semi-solid slurry lie mainly on the formation and evolution of liquid phase during remelting of the alloy. As-cast microstructure of AZ91D alloy was improved with rare earth (RE) 0.5% addition. The microstructural evolution was studied during semi-solid isothermal treatment, and the mechanism of fabrication and controlling of non-dendritic microstructure was discussed. The results indicate that the transformation from the primary phase to spheroid particle is accelerated, and the fine and symmetrical spheroid grains are gained by rare earth (RE) alloying during semi-solid isothermal treatment of magnesium alloy AZ91D. It is proposed that the microstructure in specimen is in dynamic equilibrium state of melting and crystallizing during semi-solid isothermal treatment. The high solute concentration area at dendrite root of the as-cast alloy, or the temperature/ composition fluctuations is the internal or external conditions of liquid formation in solid particle.
Key words: magnesium alloy; rare earth; semi-solid state; microstructural evolution
