【作者】 吴国华； 张亮； 胡钊华； 丁文江；

【Author】 WU Guo-hua;ZHANG Liang;HU Zhao-hua;DING Wen-Jiang;National Engineering Research Center of Light Alloys Net Forming, Shanghai Jiao Tong University;

【机构】 上海交通大学材料学院轻合金精密成型国家工程研究中心；

【摘要】 过共晶Al-Si合金,尤其是高硅铝合金,是发展高强耐磨耐高温铝合金的重要方向之一。但是,Si含量的提高导致合金析出粗大的初生硅,严重割裂基体并显著降低力学性能,极大地阻碍了该系列合金的应用推广。因此,开发一种能够有效细化初生硅尺寸、改善合金性能的工艺方法是很有必要的。现有的流变压铸研究集中在低Si含量的共晶、亚共晶Al-Si合金上,关于过共晶Al-Si合金的研究基本处于空白。过共晶Al-Si合金,尤其是高硅铝合金的流变压铸成形研究,有望实现初生硅细化的目标,同时克服常规液态铸造下的缺点,获得优良的微观组织和力学性能,并为过共晶Al-Si合金半固态流变成形技术的开发和应用提供理论指导和实践依据。本文以Al-15Si-4Cu-0.5Mg和Al-20Si合金为研究对象,系统研究了机械旋转滚筒制浆工艺对流变浆料组织的影响;研究了RE (La、Ce)变质和流变加工复合处理对流变浆料微观组织的影响。采用优化的最佳流变制浆工艺和复合制浆工艺对Al-15Si-4Cu-0.5Mg和Al-20Si合金进行流变压铸成形,研究其微观组织和力学行为,探讨其强化机理。通过研究不同滚筒转速和浇注温度下Al-15Si-4Cu-0.5Mg和Al-20Si合金添加RE (La, Ce)前后流变浆料的组织演变,探明了机械搅拌制浆和复合制浆的影响规律。阐明了稀土变质和流变加工复合处理对初生硅生长的影响。机械滚筒引起的激冷效应可以有效提高初生硅颗粒的形核率,其高速转动引起熔体的强对流促使更多的稀土元素被吸附到初生硅<112>方向的生长前沿,提高"杂质诱发孪晶"效率;另一方面,在温度均匀的环境下,均匀分布的稀土元素以稀土化合物的形式包围、甚至紧贴着初生硅析出,进一步阻碍其生长,起到细化作用。将优化的Al-15Si-4Cu-0.5Mg合金流变制浆工艺成功用于车用空调压缩缸体的生产,制备的产品质量优良、可热处理,其耐压性能远远高于高压铸造,表明过共晶Al-Si合金流变加工工艺具有巨大的工业应用价值。更多还原

【Abstract】 Hypereutectic Al-Si alloy, especially high Si Al-Si alloy, are important directions in the development of high strength, wear resistance and high temperature resistance Al alloy. However, the coarse primary Si particles will be obtained as the Si content increased, which severely worsen the mechanical property and limit its widely application. Therefore, it is necessary to develop a new processing technique that can effectively refine the primary Si and increase the mechanical property of hypereutectic Al-Si alloy. To date, researches about rheo-diecasting of Al-Si alloy mainly focus on eutectic and hypoeutectic Al-Si alloys, references on hypereutectic Al-Sialloy are rare. Researches on hypereutectic Al-Si alloy, especially high Si content Al-Si alloy, are of great prospects in refinement of primary Si, overcoming the defects of liquid casting, achieving excellent microstructure and mechanical property, and providing theoretical guides and experimental datum for the development of rheo-diecasting technique of hypereutectic Al-Si alloys.The present work systematically investigated the effects of processing parameters of the Mechanical rotational barrel(MRB) and the combined treatment of RE modification and rheo-processing of MRB(CTRMR) on the microstructures of the semisolid slurry of Al-15 Si-4 Cu-0.5 Mg and Al-20 Si alloys. Then, adopted the optimized rheo-processing parameters to rheo-diecast the Al-15 Si-4 Cu-0.5 Mg and Al-20 Si alloys and investigated their microstructures and mechanical properties. Similarly, adopted the optimized the combined treatment of RE modification and rheo-processing of MRB parameters to rheo-diecast the Al-15 Si-4 Cu-0.5 Mg and Al-20 Si alloys and investigated their microstructures, mechanical properties and strengthening mechanism. In order to investigated the rules that MRB processing parameters work on semisolid slurry, the slurry microstructural evolution of the Al-15 Si-4 Cu-0.5 Mg and Al-20 Si alloy under different rotational speeds and pouring temperature were studied. Meanwhile, the rules of the combined treatment of RE modification and rheo-processing of MRB that affected the semisolid slurry, the slurry microstructural evolution of the Al-15 Si-4 Cu-0.5 Mg and Al-20 Si alloy with 0.5 wt% RE(La, Ce) under different rotational speeds and pouring temperature were studied. The present work illuminated the effects of CTRMR on the growth of primary Si. The chilling effects effectively increased the nucleation rate of the primary Si, and the strong melt convection generated by MRB made more La and Ce atoms absorbed onto the Si growth front along the <112> directions, which greatly improved the impurity induced twinning effect. The La and Ce elements became more homogeneous by rheo-processing, which during solidifying period surround or stick to the primary Si and hinder its further coarsening. The optimized slurry preparation parameter was successfully used to rheo-diecast the compressive cylinder for automobile air conditioner of Al-15 Si-4 Cu-0.5 Mg alloy. The products were excellent in quality and could be heat treated, with much higher compressive ability than conventional high pressure die casting products, which show that the rheo-processing technology of hypereutectic Al-Si alloy is of great values to be applied to the industry production.更多还原