(1. 北京有色金屬研究總院，北京 100088;
2. 北京科技大學(xué) 新金屬材料國家重點實驗室，北京 100083;
3. Brunel University, Uxbridge, Middlesex UB8 3PH, UK)
摘 要: 采用雙螺旋流變鑄造技術(shù)制備鎂合金AZ61鑄錠，并與常規(guī)鑄造組織進(jìn)行對比。常規(guī)鑄造得到粗大的樹枝晶，而流變鑄造得到細(xì)小的球狀晶，平均晶粒尺寸約40 μm。采用常規(guī)熱擠壓工藝和流變擠壓工藝分別擠壓出直徑22 mm的棒材，分析比較流變擠壓與常規(guī)熱擠壓過程中，擠壓力大小和擠壓速率的關(guān)系，觀察不同工藝下得到的微觀組織。結(jié)果表明，常規(guī)擠壓為動態(tài)再結(jié)晶組織，晶粒形狀和大小與擠壓溫度和速度密切相關(guān)；流變擠壓中漿料在通過擠壓模時凝固，得到平均晶粒尺寸約8 μm的鑄態(tài)組織，其原因是大量二次形核的核心得以存留并長大。
關(guān)鍵字: 鎂合金；流變鑄造；流變擠壓；二次形核
（1. General Research Institute for Nonferrous Metals, Beijing 100088, China;
2. State Key Laboratory for Advanced Metals and Materials, University of Science and
Technology Beijing,Beijing 100083, China;
3. Brunel University, Uxbridge, Middlesex UB8 3PH, UK）
Abstract:The microstructure of AZ61 Mg alloy made by the methods of normal cast and twin-screw rheo-cast was investigated. The grains are coarse dendrite in normal cast billet, while they are tiny ground grains in rheo-cast billet with the average grain size of about 40 μm. The d 22 mm rods were fabricated by hot extrusion and rheo-extrusion separately, the microstructure of these rods and the relationship between the extrusion force and velocity were researched. The result shows that dynamic recrystallization happens in the hot extrusion, the shape and size of the grains are determined by the extrusion temperature and velocity. In the process of rheo-extrusion, slurry solidification occurs and the tiny ground grains form in the extrusion mould with the average grain size of about 8 μm. The reason of grain refinement is that lots of nucleus formed in the secondary nucleation get survived and grow up.
Key words: magnesium alloy; rheo-cast; rheo-extrusion; secondary nucleation
