(1. 南昌大學(xué) 材料科學(xué)與工程學(xué)院，南昌 330031；2. 南昌大學(xué) 機(jī)電工程學(xué)院，南昌 330031)
摘 要: 研究LSPSF工藝條件下Al-20%(質(zhì)量分?jǐn)?shù))Cu合金的初生α(Al)的形貌演變，結(jié)合微觀組織模擬技術(shù)和M-S界面形態(tài)穩(wěn)定性理論，分析過冷熔體中球晶組織快速形成的基本規(guī)律。結(jié)果表明：合金熔體中自由晶數(shù)目和漿料冷卻速度共同決定初生固相的尺寸和形態(tài)；最早(凝固發(fā)生3 s內(nèi))觀察到的初生α(Al)呈細(xì)小球形，并在整個(gè)演變過程中始終保持球形不變，沒有枝晶組織出現(xiàn)；晶粒周圍溶質(zhì)擴(kuò)散層的疊加可明顯降低固−液界面前沿的濃度梯度，提高固−液界面的穩(wěn)定性；均勻化晶粒周圍溶質(zhì)分布，抑制晶粒的擇優(yōu)生長(zhǎng)，促進(jìn)初生α(Al)保持球形；由溶質(zhì)擴(kuò)散層的疊加和界面能引起的抑制和粗化效應(yīng)可促使失穩(wěn)的等軸晶粗化成球晶。
關(guān)鍵字: 半固態(tài)成形；凝固；晶體生長(zhǎng)；界面穩(wěn)定性；微觀組織模擬
（1. School of Materials Science and Engineering, Nanchang University, Nanchang 330031, China;2. School of Mechanical and Electronic Engineering, Nanchang University, Nanchang 330031, China）
Abstract:The microstructure evolution of Al-20%(mass fraction)Cu alloy under LSPSF (Low superheat pouring with a shear field) conditions was investigated. The quick formation mechanism of spherical particles in an undercooled melt was discussed by microstructure simulation technique and M-S interface stability theory. The results show that the morphology of primary α(Al) is determined by both the number of free crystals and the cooling intensity of melt. The first observable primary α(Al) of Al-20%Cu alloy is spherical shape, and grows spherically in subsequently lower cooling. The overlapping diffusion fields from adjacent growing crystals can induce a stabilizing effect on the morphological instability at the solid-liquid interface and promote the globular growth of primary α(Al). Restraining and coarsening caused by overlapping diffusion fields and Gibbs-Thomson effect are main dynamic conditions that promote the morphology transition of instabilized crystal from equiaxed shape into spherical shape.
Key words: semi-solid metal processing; solidification; crystal growth; interface stability; microstructure simulation
