Al-7Si-Mg合金凝固过程形核模型建立及枝晶生长过程数值模拟  

NUCLEATION MODEL AND DENDRITE GROWTH SIMULATION IN SOLIDIFICATON PROCESS OF Al-7Si-Mg ALLOY

作　　者：陈瑞[1] 许庆彦[1] 吴勤芳 郭会廷 柳百成[1] 

机构地区：[1]清华大学材料学院先进成形制造教育部重点实验室,北京100084 [2]明志科技有限公司,苏州215006

出　　处：《金属学报》2015年第6期733-744,共12页Acta Metallurgica Sinica

基　　金：国家重点基础研究发展计划项目2011CB706801;国家自然科学基金项目51374137和51171089;国家科技重大专项项目2012ZX04012-011和2011ZX04014-052资助~~

摘　　要：针对铝合金砂型铸造较低冷速特点,通过实测和分析不同凝固条件下的冷却曲线,建立了适用于铝合金形核密度随最大形核过冷度呈指数性变化的形核函数.通过与Pandat软件热力学、动力学、平衡相图数据库相耦合,并利用空间坐标变化等算法,建立了适用于三元铝合金二维、三维枝晶生长的CA模型.在该模型中,同时考虑了溶质扩散、成分过冷、曲率过冷、晶体择优取向以及不同组元之间相互作用等重要因素的影响.利用建立的形核和生长模型,模拟了Al-7Si-0.36Mg合金在不同凝固条件下的二维枝晶演化及形貌特征,描述了溶质组元的分布特征以及定量地预测了二次枝晶臂间距的变化,并与实验结果进行了对比.三维枝晶的模拟结果有效反映了枝晶空间结构复杂性和多样性,并与实验结果吻合良好.Due to the extensive applications in automotive and aerospace industries of A1-7Si-Mg casting al- loys, its tmderstanding of the dendrite microstructural formation is of great importance to control the desirable mi- crostructure and thereby to modify the performance of castings. In this work, through analyzing the measured cool- ing curves in different cooling conditions of A1-7Si-0.36Mg ternary alloy during sand casting, a theoretical nucle- ation model correlated maximum nucleation undercooling with the nucleation density is proposed. Besides, a 2D and 3D cellular automaton （CA） model allowing for the quantitatively predicting dendrite growth of ternary alloys is presented. This model introduces a new tracking neighboring rule algorithm to eliminate the effect of mesh de- pendency on dendrite growth. The thermodynamic and kinetic data needed in the simulations is obtained by cou-pling with Pandat software package in combination with thermodynamic/kinetic/equilibrium phase diagram calculation databases. This model has also taken account the multi-component diffusion, constitutional undercooling, cur-vature undercooling, dendrite preferential growth angles as well as the effect of interactions between the alloying elements etc. This model is applied to quantitatively simulate the dendrite growth with various crystallographic ori- entations of AI-7Si-0.36Mg ternary alloy in 2D and 3D during polycrystalline solidification, and the predicted sec- ondary dendrite arm spacing （SDAS） shows a reasonable agreement with the experimental results. The experimen- tal observed complicated and diverse dendrite microstructure occurring in solidification process can be well repro- duced by this 3D-CA model which has considered the effects of various preferred growth orientations, the interac- tions of adjacent dendrites as well as the influence of S/L interface anisotropies. The simulated results effectively demonstrated the abilities of this model in prediction of dendrite microstructure in ternary alloys.

关 键 词：三元铝合金 形核模型 元胞自动机 枝晶生长 二次枝晶臂间距 

分 类 号：TG114.4[金属学及工艺—物理冶金]