多元稀土对半固态A356铝合金梯度细化的研究

摘要

基于稀土在铝合金中诱发共晶反应进而细化凝固组织的机制,设计了Gd-Nd-Y-Ce四元稀土复合细化剂,并辅以梯度保温措施,使半固态A356铝合金在保温阶段按照Al-RE共晶温度由高到低依次发生共晶反应,提高共晶产物的保存率,进而研究多元稀土对半固态A356铝合金凝固组织的梯度细化效果.结果表明:四元稀土按照正交试验设计的百分比添加量加入,在650℃浇注,并按照645℃/30 s-635℃/40 s-625℃/50 s-615℃/60 s进行梯度保温,615℃水淬脱模后,借助公式获得不同试样的细化特征参量.采用综合平衡法,对正交试验获得的极差R和试验指标Ki进行参数分析,获得四元稀土在优化方案下的最佳配比为:0.5％Gd+0.2％Nd+0.4％Y+0.2％Ce,试验验证此时A356铝合金初生相的平均等积圆直径为83.013μm,形状因子为0.817,细化效果最好.%Based on the mechanism of refining solidification structure resulted from eutectic reaction induced by rare earth in aluminum alloy, the Gd-Nd-Y-Ce quaternary rare earth composite refiner was designed, supplemented by gradient thermal insulation measures. Through making the semisolid A356 aluminum alloy in heat preservation phase in accordance with the Al-RE eutectic temperature from high to low successive eutectic reaction, to improve the survival of eutectic products was ensured. The effect of complex rare earth on semisolid A356 aluminum alloy solidification gradient refining was researched. The results show that the addition contents of quaternary rare earth were determined according to the orthogonal experiment design. Under the conditions of 650 ℃pouring temperature, and gradient thermal insulation according to the 645 ℃/30 s-635 ℃/40 s-625 ℃/50 s-615 ℃/60 s, and 615℃water quenching demould, the refining characteristic parameters of different samples were obtained through the formula. By comprehensive balance method, analysis of the extreme-difference R and test-index Ki of the orthogonal experiment parameters, the optimal proportion of the quaternary rare earth was found as follows: 0.5％Gd+0.2％Nd+0.4％Y+0.2％Ce. The primary phase A356 aluminum alloy of average equal-area diameter is 83.013μm, and the shape factor is 0.817, the refining effect is best.