新型Al-5Ti-1B-7Sm细化变质剂对亚共晶Al-Si合金组织及性能的影响

发布时间：2018-05-08 12:07

  本文选题：ZL114合金 + Al-Ti-B-Sm　； 参考：《哈尔滨理工大学》2017年硕士论文

【摘要】：亚共晶Al-Si合金因强度高、密度小等优点而备受瞩目,但它在凝固过程中会出现粗大、易偏聚的初生α-Al相和片层状共晶硅组织,严重降低合金力学性能。细化变质是改善合金组织的重要方法,在工业生产中得到了广泛应用。本文以ZL114铝合金为研究对象,首先以1wt.%Al-5Ti-1B和变量稀土Sm对ZL114合金联合细化变质为基础,制备最优Al-5Ti-1B-XSm细化变质剂,然后采用Al-5Ti-1B-XSm细化变质剂研究细化变质时间和温度对ZL114合金组织及性能的影响规律并探讨其细化变质机理。首先,固定Al-5Ti-1B的加入量为1 wt.%,改变Sm的加入量探索最佳的Al-5Ti-1B-XSm细化变质剂。结果表明,随着Sm的加入量增加,α-Al相的二次枝晶臂间距和共晶硅的平均长径比先减小后增加,当Sm的加入量为0.07 wt.%时,α-Al相二次枝晶臂间距和共晶硅平均长径比最小,分别为11.24μm和2.53,抗拉强度和显微硬度最高,分别为225 MPa和63.2。根据原子守恒,自制的细化变质剂为Al-5Ti-1B-7Sm。Al-5Ti-1B-7Sm中第二相主要为Ti_2Al_(20)Sm和TiB_2,其中Ti B2分布弥散,无偏聚现象。采用1 wt.%Al-5Ti-1B-7Sm细化变质剂对ZL114合金细化变质的最佳工艺为720℃×60 min,此时α-Al相二次枝晶臂间距和共晶硅长径比最小,分别为9.28μm和1.84,显微硬度和抗拉强度最高,分别为70.4和265 MPa。拉伸断口附近出现韧窝,断裂面细化明显,断裂方式为韧性断裂。细化变质机理分析表明,Ti2Al20Sm与α-Al有8组可能匹配的取向关系,可作为α-Al异质形核质点,提高α-Al细化程度。合金经1 wt.%Al-5Ti-1B-7Sm细化变质后,初晶形核温度提高到609.7℃,且初晶凝固时间减少,初晶长大受到抑制;共晶形核温度为567.5℃、共晶凝固时间2.6 s,均较未变质合金有较大程度降低,形核核心减少、凝固时间的缩短是共晶硅转变为纤维状的主要原因。此外,共晶生长速度降低及粗糙型界面特征是共晶硅变质为纤维状的其他因素。
[Abstract]:Hypoeutectic Al-Si alloy has attracted much attention because of its high strength and low density. However, it will produce coarse and easily segregated primary 伪 -Al phase and lamellar eutectic silicon during solidification, which seriously reduces the mechanical properties of the alloy. Refined modification is an important method to improve the microstructure of alloys and has been widely used in industrial production. In this paper, ZL114 aluminum alloy was used as the research object. Firstly, based on the combined refinement and modification of ZL114 alloy by 1wt.%Al-5Ti-1B and variable rare earth Sm, the optimal Al-5Ti-1B-XSm refiner was prepared. Then the effect of modification time and temperature on the microstructure and properties of ZL114 alloy was studied by using Al-5Ti-1B-XSm refiner and the modification mechanism was discussed. Firstly, the amount of fixed Al-5Ti-1B is 1 wt. to change the amount of Sm to find the best Al-5Ti-1B-XSm refiner. The results show that the secondary dendritic arm spacing of 伪 -Al phase and the average aspect ratio of eutectic silicon decrease first and then increase with the increase of Sm content. When Sm is 0.07 wt.%, the distance between the secondary dendritic arms of 伪 -Al phase and the average length / diameter ratio of eutectic silicon is the smallest. The tensile strength and microhardness were the highest, which were #number0# MPa and 63.2 渭 m, respectively, with 11.24 渭 m and 2.53 渭 m, respectively. According to atomic conservation, the second phase in Al-5Ti-1B-7Sm.Al-5Ti-1B-7Sm is mainly Ti_2Al_(20)Sm and TiB-2, in which the distribution of TiB2 is dispersed and the phenomenon of unbiased aggregation is observed. The optimum process for refining and modifying ZL114 alloy with 1 wt.%Al-5Ti-1B-7Sm refining modifier is 720 鈩，

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