(1. 南昌航空大學(xué) 江西省金屬材料微結(jié)構(gòu)調(diào)控重點(diǎn)實(shí)驗(yàn)室，南昌 330063；
2. 南昌航空大學(xué) 輕合金加工科學(xué)與技術(shù)國(guó)防重點(diǎn)學(xué)科實(shí)驗(yàn)室，南昌 330063)
摘 要: 采用真空感應(yīng)熔煉與階梯銅模噴鑄相結(jié)合，制備出微米/納米SiC參與下快冷鎂合金，研究SiC尺寸對(duì)非平衡凝固鎂合金異質(zhì)形核及組織細(xì)化的影響。結(jié)果表明：冷速的提高與SiC的添加共同促進(jìn)鎂合金的復(fù)合細(xì)化，其中銅模噴鑄條件下微米SiC的細(xì)化效果更佳。當(dāng)銅模內(nèi)徑di=4 mm，添加2%的微米SiC(質(zhì)量分?jǐn)?shù))后快冷鎂合金平均晶粒尺寸減小到5 μm以內(nèi)。經(jīng)(400 ℃, 2 h)等溫固溶處理后，快冷合金晶界處的離異共晶β-Mg17Al12相消失，初生α-Mg晶粒由細(xì)小薔薇狀向多邊形組織發(fā)生轉(zhuǎn)變。通過(guò)枝晶生長(zhǎng)與溶質(zhì)截留模型的理論計(jì)算，銅模噴鑄條件下獲得的過(guò)冷度范圍為67~80 K，所對(duì)應(yīng)的臨界形核半徑為0.115~0.116 μm，因此，更有利于微米SiC對(duì)鎂合金的組織細(xì)化。
關(guān)鍵字: 非平衡凝固；異質(zhì)形核；枝晶生長(zhǎng)；組織細(xì)化；鎂合金
（1. Key Laboratory for Microstructural Control of Metallic Materials of Jiangxi Province, Nanchang Hangkong University, Nanchang 330063, China;
2. National Defence Key Discipline Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University, Nanchang 330063, China）
Abstract:With the combination of vacuum induction melting and spray casting by step copper mould, rapid cooled magnesium alloys containing micro/nano SiC were fabricated, and then the influence of particle size of SiC on heterogeneous nucleation and microstructure refinement was investigated. The results show that both the increase of cooling rate and the addition of SiC promote grain refinement of magnesium alloy, whereas, the effect of SiC with micron size is better than that with nano under spray casting condition. As for the copper mould with inner diameter di=4 mm, the addition of 2% micron SiC generates the reduction of average grain size within 5 μm. After solid solution treatment at 400 ℃ for 2 h, the grain morphology of primary α-Mg phase transits from fine rosette to polygon, accompanied by the disappearance of divorced eutectic β-Mg17Al12 phase at grain boundary. According to the theoretical calculation of dendrite growth and solute trapping model, the obtained undercooling range for spray casting is 67-80 K，which corresponds to the critical nucleation radius with 0.115-0.116 μm. Consequently, SiC particle with micron size is advantageous for microstructure refinement.
Key words: non-equilibrium solidification; heterogeneous nucleation; dendrite growth; microstructure refinement; magnesium alloy
