(南昌航空大學 輕合金加工科學與技術國防重點學科實驗室，南昌 330063)
摘 要: 采用銅模噴鑄與真空感應熔煉相結合，研究了Y含量(質(zhì)量分數(shù))對快冷Mg-6Al合金非平衡凝固組織及力學壓縮性能的影響。通過稀土相結構及形貌分析對合金晶粒細化規(guī)律進行闡述。結果表明：銅模噴鑄Mg-6Al合金組織顯著細化，平均晶粒尺寸由鑄態(tài)時的200 μm降低到24.5 μm，同時初生α-Mg相形貌從粗大不規(guī)則花瓣狀向細小等軸枝晶轉(zhuǎn)變。隨Y含量增加，快冷Mg-6Al合金組織出現(xiàn)先細化后粗化趨勢，其中添加1%Y時合金中形成方塊狀或棒狀Mg24Y5相，能夠促進異質(zhì)形核，細化效果最佳，平均晶粒尺寸僅13 μm，相應壓縮強度高達404 MPa。當Y含量過多時，快冷Mg-6Al-1.25Y合金中Mg24Y5相易發(fā)生團聚，從而弱化組織細化效果。
關鍵字: 稀土；鎂合金；快速凝固；組織細化；異質(zhì)形核
（National Defence Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:Effects of Y content on microstructure evolution and compression strength of rapidly cooled Mg-6Al alloy were investigated by injection casting into copper mould under the protection of vacuum induction melting. Both the structure and morphology of RE-rich phase were identified to reveal the refinement mechanism. The results show that the microstructure of rapidly cooled Mg-6Al alloy is significantly finer than that of the as-cast state, as indicated by the reduction of average grain size from 200 μm to 24.5 μm. Moreover, the grain morphology varies from coarse irregular petal to fine equiaxed dendrite. With the increase of Y content, the microstructure of rapidly cooled Mg-6Al alloy appears to be refined firstly and then coarsened. Square block or rod-shape Mg24Y5 phase forms in the ingot with the addition of 1%Y, which promotes heterogeneous nucleation of primary phase and is beneficial to grain refinement. Consequently, the minimum average grain size is merely 13 μm and the corresponding compression strength reaches 404 MPa. As for the sample with higher Y content, apparent agglomeration of Mg24Y5 phase occurs in Mg-6Al-1.25Y alloy, which weakens the grain refinement of rapid cooled alloy.
Key words: rare earth; magnesium alloy; rapid solidifcation; microstructure refinement; heterogeneous nucleation
