(東北大學 材料與冶金學院，沈陽 110004)
摘 要: 利用連續(xù)流變成形實驗機制備斷面為5 mm×50 mm的Mg-3Sn-1Mn鎂合金型材，研究輥靴型腔中的合金組織及其形成機理。結果表明：合金熔體首先在軋輥和靴子表面異質形核。當軋輥表面比較粗糙時，合金在軋輥表面異質形核能力較強，利于枝晶的形成；在軋輥剪切/冷卻作用下，枝晶發(fā)生破碎形成自由晶，枝晶破碎主要由枝晶臂剪切斷裂機制和枝晶臂熔斷機制引起；自由晶在生長過程中，由于合金熔體內部的層流剪切作用，自由晶進一步被破碎，晶粒周圍溶質分布趨于均勻，其散熱擇優(yōu)方向也不明顯，沿各個方向生長機會均等，晶粒以球狀晶或等軸晶形式長大。
關鍵字: 鎂合金；連續(xù)流變成形；半固態(tài)；組織；機理
during continuous rheo-forming process
（School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China）
Abstract:Mg-3Sn-1Mn alloy profiles with cross-section size of 5 mm×50 mm were prepared by the continuous rheo-forming process, and the microstructures and formation mechanisms of the alloy in the roll-shoe gap were investigated. The results show that the heterogeneous nucleation of the alloy occurs firstly on the surface of roll-shoe. When the roll surface is rough, the heterogeneous nucleation capability of the alloy is stronger on the roll surface, which is favorable to the formation of dendrites. The dendrites are broken up to form free grains under the action of cooling/shearing of the roll. The dendrite fragmentation is caused by the shearing fracture mechanism of dendritic arms and the blowing-out mechanism of dendritic arms. During the growing process of free grains, because of laminar shearing caused by the roll, the free grains are broken up further, the solute distribution around free grains is homogenous, the preferred orientation of heat dissipation is not obvious, the growing chances of grains are equal in all directions, and the grains grow in golobular or equiaxed form.
Key words: magnesium alloy; continuous rheo-forming; semisolid; microstructure; mechanism
