【作者】 陈磊；

【导师】 涂赣峰； 高波；

【作者基本信息】 东北大学 ， 有色金属冶金， 2008， 硕士

【摘要】 稀土能否变质初晶硅一直存在着争论,本课题针对这一问题进行了研究,采用常规铸造工艺方法制备实验材料,研究单一稀土Nd对不同硅含量的过共晶铝硅合金的变质作用,讨论了稀土加入量对Al-17.5Si、Al-25Si和A390合金的变质效果。并研究了挤压处理,热处理等手段对A390-0.3wt%Nd合金的组织及力学性能的影响。借助X衍射仪、扫描电子显微镜、电子万能试验机和高速高温摩擦磨损实验机等分析测试手段,研究了稀土变质机理,热处理及挤压处理对材料的微观组织结构的影响和材料的性能,并探讨了合金微观组织和力学性能之间关系,为研制新型过共晶铝硅合金提供了一种新的途径。研究表明,稀土Nd能够同时变质共晶硅和初晶硅；Nd对初晶硅的变质可用成分过冷理论和吸附理论两种作用机制的共同作用来解释。稀土Nd对Al-17.5Si、Al-25Si二元合金的变质表明,Al-17.5Si中的初晶硅呈现板状,变质后没有形态上的变化,但是平均尺寸分别由34.73μm下降到23.39μm,经过0.3%稀土Nd变质的合金抗拉强度和屈服强度分别为240MPa和130MPa,分别提高了11.6%和1.5%,磨损量下降了51.1%。Al-25Si合金由变质前的星状与不规则形态转变为多面体的板块状；平均直径从94.06μm下降到50μm以下；经过0.3%稀土Nd变质的合金抗拉强度和屈服强度分别为117.5MPa和94MPa；分别提高了22.1%和9.5%；磨损量下降了66.7%,摩擦系数显著降低；热处理能够使共晶硅粒化。对A390变质作用的研究表明,稀土Nd对A390合金变质作用不明显,主要是由于Cu2NdSi相的生成,削弱了Nd的合金变质作用；热处理试验研究表明,使共晶硅粒化,钝化初晶硅；经过挤压形变处理后A390的变质合金塑性显著提高,延伸率由0.5%提高到13.25%。本课题的特色在于首次提出了稀土对不同形态硅变质效果的差异,采用单一稀土Nd作为变质剂,是对过共晶铝硅合金变质机理的必要补充,为研制高性能过共晶铝硅合金结构材料和耐磨材料提供了一定的理论依据。更多还原

【Abstract】 The paper investigated the modification effect of rare earth to the primary silicon of hypereutectic Al-Si alloy. Experiment materials were prepared by routine cast process and the modification effect to hypereutectic Al-Si alloys with different Si content were investigated. In this paper Al-17.5Si、Al-25Si alloy and A390 hypereutectic aluminum silicon alloys were selected to investigate the effect of RE Nd addition,heat treatment and extruding processing on microstructure and mechanical of these alloys by XRD, SEM and mechanical properties test. The relations between microstructure and mechanical properties and modifcation mechanism were discussed and presented a new way to fabricate high performance hypereutectic Al-Si alloy.The experiment results show that pure Nd (0.3wt%) can refine both eutectic silicon and primary silicon in binary hypereutectic Al-Si alloy. The modification mechanism of primary silicon can be explained reasonably by undercooling theory and adsorbing theory simultaneously. There is no obviously change in morphology of primary silicon in Al-17.5Si alloy after modification, but after Nd modification treatment the average size reduced from 34.73μm to 23.39μm, mechanical properties of tensile and yield strength reach 240MPa and 130MPa increased 11.6% and 1.5% respectively; the abrasive wear and tear rate of the modified alloy reduced 51.1%. The morphology of primary silicon Al-25Si alloy change from star-sharped and irregular to plated sharp after modification, and the average size reduced from 94.06μm to 50μm. The tensile and yield strength of Al-25Si modified alloy reach 117.5MPa and 94MPa and were improved 22.1% and 9.5% respectively, the wear rate of the modified alloy reduced 66.7% and the coefficient of friction reduced obviously. The morphology of eutectic silicon particles in Al-25Si-0.3wt%Nd alloy granulate after heat treatment. The experiment results show that the addition of rare earth Nd has little modification effect on primary silicon phases in A390 alloy, as expected for the formation of the compounds of Cu2NdSi reduced modification effect of rare earths, after heart treatment the eutectic silicon spheroidized in A390, the plastic property of A390 alloy improved dramatically and elongation percentage increased from 0.5% to 13.25%.It is the first time to propose that modification effect of Nd element on varying morphology primary silicon is different. the results supplied a new way to develop high mechanical properites hypereutectic Al-Si alloy.更多还原