采用液淬方法对Al-11.80Cu-24.22Mg(质量分数, %)三元包共晶合金在不同温度下淬火, 而后, 对其相组成和凝固组织进行了研究, 对凝固组织的演化规律以及凝固机制进行了分析. 实验结果表明, 该合金凝固过程中确实发生了三元包共晶反应, 初生相为S相 (Al2CuMg), 包共晶组织为α-Al相和T相(Al6CuMg4)组成, 最终凝固组织由残余初生S相、包共晶组织 (α-Al+T)、两相共晶(α-Al+T)及三相共晶(α-Al+T+β)组成; 虽然包共晶组织中和两相共晶中含有相同的相, 即α-(Al)相和T相, 但二者的组织形态不同, 包共晶组织呈“条带状”, 而两相共晶呈规则的 “蛛网状”和“球状”. 此外, 三元包共晶反应时, 包共晶组织依附于初生S相的周围生长, 随着冷却速率的增加, 三元包共晶反应变慢甚至被抑制, 致使初生S相剩余而滞留在基体中.
In the field of condensed matter physics and materials science, it is of great importance to investigate the microstructures, properties and solidification regularities of liquid metals. In the last few decades, the theories of solidification of binary alloys, such as dendritic growth and eutectic growths have been built. Great progress has also been made on the study of monetectic and peritectic alloys. But a solidification theory on ternary quasiperitectic alloys has not been established up to now. The study of the solidification process of quasiperitectic alloys will provide a basic work for solidification theories of ternary alloys.
The master alloy of Al-11.8Cu-24.22Mg was prepared from pure Al (99.99%), pure Mg (99.99%) and Al-54.2Cu in a resistance furnace under CO2 and SF6 (volume proportion is 40∶1) atmosphere. The melted alloy (840-850℃) was pouring into different quenching graphite crucibles at the same time, and the cooling curves were recorded by a sixteen channels temperature recorder. The graphite crucible was quenched into cold--water immediately for rapid cooling at the preplanned quenching temperature. After the experiment, the microstructures of the sample were analyzed by SEM, with EDS analysis.
The experiment result indicates that the primary phase is identified as S (Al2CuMg) and the quasiperitectic phases are α-Al and T (Al6CuMg4). The solidification microstructure is composed of remnant primary phase, quasiperitectic phases, binary eutectic and ternary eutectic. Although the quasiperitectic phases and binary eutectic are composed of the same phases (α-Al+T(Al6CuMg4)), their structures are different. The former structure presents strip form and the later present dendritic form. The ternary eutectic reaction is suppressed and the remnant primary S phase is reserved in the matrix with non-equilibrating crystallization.
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