(東北大學(xué) 材料與冶金學(xué)院， 沈陽 110004)
摘 要: 采用SCR(shearing-cooling-roll)技術(shù)制備了A2017半固態(tài)合金， 對(duì)合金液在不同溫度下進(jìn)行澆注，且對(duì)輥-靴型腔中合金組織的演化過程進(jìn)行了跟蹤，分析了SCR過程中凝固形核的熱力學(xué)條件以及層流剪切特性。結(jié)果表明： 隨著合金液澆注溫度的降低， 坯料內(nèi)部組織從粗大的枝晶或菊花晶轉(zhuǎn)化為細(xì)小的近球形晶。 合金液首先在軋輥和靴子表面結(jié)晶形核， 在液流沖擊及剪切的作用下，晶核從型壁上脫落進(jìn)入殘余液相形成游離晶； 隨著輥-靴型腔內(nèi)合金固相率的增加，游離晶在以枝晶方式生長(zhǎng)過程中受到層流剪切作用， 二次枝晶臂斷裂破碎形成自由晶； 自由晶在層流剪切作用下進(jìn)一步發(fā)生碰撞和摩擦， 最后逐漸趨于球形或橢球形。
關(guān)鍵字: 材料合成與加工工藝； 半固態(tài)； 剪切與冷卻； A2017合金； 組織演化
produced by SCR process
LI Ying-long， CAO Fu-rong
（School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China）
Abstract: SCR(shearing-cooling-roll) process was adopted to manufacture A2017 semi-solid alloys. Molten alloy was poured at different temperatures. The microstructural evolution of the alloy in the roll-shoe gap was studied. The thermodynamics of nucleation and the laminar shear of molten alloy were analyzed. The results show that microstructures are transformed from dendritic or rosette-shaped to fine net-globular as decreasing pouring temperature of molten alloy. Nuclei form at the surface of roll-shoe firstly and then these nuclei are broken and enter the liquid region to form free nuclei under the impact of liquid flow and laminar shearing and grow into dendrites. Under the laminar shearing caused by the roller, the arms of the original dendrites are then broken and distributed dispersedly into residual alloy liquid and form free grains. Free grains move and grow freely continuously and are ground under the laminar shearing and cooling then become spherical or ellipsoidal.
Key words: synthesizing and process technology； semi-solid； shearing and cooling； A2017 alloy； microstructure evolution
