(1. 华南理工大学 材料科学与工程学院，广州 510640;
2. 广州钢铁企业集团有限公司 有色金属研究所，广州 510340)
摘 要: 采用金相显微镜、SEM、EDS和差示扫描量热法(DSC)等手段研究混合稀土(RE)合金添加量对Ti-B-Sr联合细化变质的A356 铝合金显微组织结构的影响。结果表明：当稀土添加量为0.1%~0.3%(质量分数)时，随着稀土含量的增加，初晶晶胞尺寸、硅相尺寸、二次枝晶臂间距减小，硅相圆整度提高(长径比降低)；当稀土添加量为0.3%时，初始α(Al)相的平均枝晶胞尺寸为76 mm，二次枝晶间距为11.3 mm，Si相长径比为2.13；加入0.1%~0.3%的稀土降低了合金的共晶点温度和初晶a(Al)的形核温度，并减小组织熔化过程中共晶反应的放热量。
关键字: A356铝合金；稀土； 混合稀土；晶粒细化；变质处理； 微观组织
microstructures of A356 alloy
（1. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China;
2. Non-ferrous Metal Research Institute，Guangzhou Iron and Steel Enterprises Holding Co. Ltd., Guangzhou 510340, China）
Abstract:The effect of RE addition on the microstructures of A356 alloys refined and modified with Ti-B-Sr was investigated by optical microscopy, scanning electron microscopy, energy dispersive spectrometry and differential scanning calorimetry. With the increase of the RE mass fraction in the range of 0.1%−0.3%, the size of primary α(Al) cell, the size of silicon phase and the secondary dendrite arm spacing decrease, and the aspect ratio of silicon phase increases. When the mass fraction RE added is 0.3%, the average size of primary α(Al) cell, the secondary dendrite arm spacing and the aspect ratio of silicon phase are 76 μm, 11.3 μm and 2.13, respectively. 0.1%−0.3％ RE addition makes eutectic temperature and nucleation temperature of primary α(Al) fall down, and lowers the eutectic reaction releasing heat.
Key words: A356 Al alloy; rare earth; mischmetal; grain refining; modification; microstructure
