【作者】 方东；

【导师】 范晓明；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 Al-Si-Mg三元合金是在Al-Si系二元合金的基础上适当降低含硅量而添加少量镁而成,加入Mg可形成Mg2Si相,能显著提高合金的时效强化能力,改善力学性能。ZA17SiMg铝合金成分简单、容易熔炼,具有良好铸造性能、气密性、焊接性能和加工性能,因此,应用广泛。铁是铝硅合金中最主要的杂质元素,硬而脆的针状Fe相会大幅降低铝硅合金的力学性能,因此,改善Fe相形貌成为降低其危害性的重要技术途径。RE及单一Ce作为变质剂,能够细化共晶硅和a-A1晶粒,但其对高铁铝硅合金中针状铁相的变质作用的相关报道较少。此外,Sr也能细化共晶硅,改善铁相形貌。关于RE+Sr复合变质的研究虽有报道,但对其变质效果的观点却并不一致。本文以高铁ZA17SiMg为基体,通过加入Ce、RE及RE+Sr制备试样,并采用光学显微镜(OM)、X射线衍射仪(XRD)、电子探针(EPMA)和INSTRON5882电子万能材料试验机等现代测试手段,研究了Ce, RE及RE+Sr复合变质对高铁铝硅合金的微观组织和力学性能的影响,分析了添加元素对合金中Fe相的改善作用机制和对α-Al枝晶及共晶硅相变质作用的机制。所得到的主要结论如下：(1)适量的Ce对高铁铝硅合金中的针状Fe相有较明显的抑制作用。Ce的加入能够有效的改善铸态高铁铝硅合金共晶硅的形貌,使其由粗大的片状转变为细小的短针状,同时α-Al晶粒也得到细化。RE及RE+Sr复合对针状Fe相、共晶硅、a-Al晶粒变质效果与Ce类似。(2)过量的Ce、RE及RE+Sr加入后,高铁铝硅合金中易形成大量针状、板块状的稀土金属间化合物,产生过变质现象。(3)适量Ce、RE及RE+Sr可以改善高铁铝硅合金的力学性能,T6热处理使合金的抗拉强度提高。在本试验条件下,合金中加入0.4%Ce、0.36%RE和0.36%RE+0.12%Sr时,对应的铸态抗拉强度达到最大值,分别为146MPa、148MPa和168MPa。经过T6热处理后,其对应的抗拉强度分别为217MPa、211MPa和213MPa。结果表明,在铸态下RE+Sr的复合变质效果要好于单一Ce或RE；T6处理后,三种变质处理的变质效果相差不大。更多还原

【Abstract】 Based on the Al-Si system binary alloy, Al-Si-Mg ternary alloy is generated by lowing silicon content and adding a small amount of magnesium.Mg2Si phase formed by adding Mg can significantly enhance the aging strengthening capacity and improve the mechanical properties. The ZA17SiMg alloy is widely used because of its simple composition, easy melting, good castability, airtightness, weldability and machinability.Iron is the most common impurity in Al-Si alloys, and the fragile iron intermetallic phase platelets deteriorate the mechanical properties significantly. So the key to eliminating the harmful effect is that the morphology of iron phase could be transformed. RE or single Ce as modifier, can refine eutectic silicon andα-Al grains. However, there were less reports about the effect of RE and Ce on Al-Si alloys with high Fe content. In addition, Sr can also refine eutectic silicon and improve the morphology of iron phase. There were some studies about the RE+Sr compound modification, but the views of its modification effect was not consistent.In this paper, the effects and mechanism of Ce、RE and RE+Sr addition on microstructures and properties of Al-Si alloy with high Fe content were studied by using modern analysis and test facilities such as optical microscopy (OM), X-ray diffraction (XRD), electron probe microanalyzer (EPMA). The mechanism of addition elements and their interaction on iron phase were analyzed, and some results having been obtained in this dissertation are as follows:Firstly, the defined amount of Ce in Al-Si alloy has significant inhibition effects on needle-like iron phase. The addition of Ce can effectively improve the morphology of eutectic silicon in as cast Al-Si alloys with high Fe content, and transformed it from coarse flake phase into fine and short needle phase. In the meantime, a-Al grains can also be refined. RE and RE+Sr compound modification effects on needle-like Fe phase, eutectic silicon and a-Al grains are analogous to Ce.Secondly, it is easy to form massive needle-like, plate-like RE compounds, and produce the excessive modification phenomenon with the addition of excess Ce, RE or RE+Sr.Thirdly, defined amount of Ce, RE and RE+Sr can improve mechanical properties of Al-Si alloys with high Fe content, and T6 heat treatment improves the tensile strength of the alloys. In the experiment, when adding 0.4%Ce,0.36%RE and 0.36%RE+0.12%Sr into the alloys, the corresponding tensile strength can reach the maximum, which are separately 146Mpa,148MPa and 168MPa. After T6 heat treatment, the corresponding tensile strength becomes 217Mpa,211Mpa and 213Mpa respectively. It is clear that the complex modification effects of RE+Sr in the as cast is better than Ce or RE, however, their effects of the three kinds of modification are little difference in T6 heat treatment.更多还原