Al-23Si-4.5Fe-3Cu-lMg合金转棒诱导形核法半固态浆料制备及压铸成形

发布时间：2018-01-15 18:39

  本文关键词：Al-23Si-4.5Fe-3Cu-lMg合金转棒诱导形核法半固态浆料制备及压铸成形　出处：《昆明理工大学》2015年硕士论文　论文类型：学位论文

  更多相关文章： 转棒诱导形核法 Al-23Si-4.5Fe-3Cu-1Mg合金 初生Si 富Fe相 流变压铸

【摘要】：Fe含量较高的过共晶铝硅合金中的初生Si、富Fe相等的形貌及分布对合金的性能有非常重要的影响。初生Si、富Fe相在A1-Si合金中作为硬质相能提高合金的耐磨性能,但是在铸造铝合金中,粗大的初生Si和长针状的富Fe相会对合金基体产生割裂作用,危害合金的力学性能。研究证明,半固态处理能有效地细化合金中的初生相,改善其形貌,提高合金的力学性能。本文采用转棒诱导形核法制备AI-23Si-4.5Fe-3Cu-1Mg合金半固态浆料,研究了不同工艺参数对合金显微组织的影响,并分析了半固态压铸条件下合金组织的变化规律。实验结果表明,转棒诱导形核法能有效改善合金显微组织,不仅能细化合金中的初生Si、还对合金组织中的富Fe相有明显的细化效果,对组织中的共晶相以及其它的物相也有相应的影响。不同工艺参数下,转棒诱导形核法对合金显微组织的影响表现出不同的规律。转棒转速变化时,合金熔体的运动状态会随之改变。转速过低时,熔体重力起主要作用,内外层熔体在转棒旋转方向的相对速度较小,熔体与转棒的接触面积较小、厚度较大。转速过高时,转棒产生的离心力起主要作用,熔体在离心力影响下会过早脱离转棒,内外层熔体相对速度虽然较大,但熔体在垂直方向上与转棒的接触面积减小,使得在高转速时熔体与转棒的接触面积减小。导热系数高的铜质转棒能在同时间内带走熔体更多的热量,其形核效果优于钢质转棒。浇注温度过高时浆料内残存热量较多,降低半固态浆料中游离晶核的密度,并产生成分过冷,促进晶粒生长。浇注温度过高时,熔体中已形成的晶粒会发生重熔的现象,降低熔体中游离晶核密度,最终长大成大尺寸晶粒。研究结果表明,采用φ75mm铜质转棒,转棒转速为600r/min,浇注温度为830℃时,合金的细化效果最佳,初生Si、富Fe相分别细化至32μm、34μm。采用压铸工艺制备了液态常规压铸件和半固态压铸件,分析了压铸件中的组织变化规律,发现压铸工艺不仅能细化合金组织中的初生Si、富Fe相等初生相,还对富Cu相、共晶组织的形态和分布有着明显的优化作用。在半固态压铸成形制备的压铸件中,初生Si和富Fe相的尺寸分别减小至15μm、20μm,并且,随压射流程的增加,显微组织中二次初生相的体积分数明显增加。
[Abstract]:The primary Si in hypereutectic Al-Si alloy with high Fe content has a very important effect on the properties of hypereutectic Al-Si alloy. Fe-rich phase as a hard phase in A _ 1-Si alloy can improve the wear resistance of the alloy, but in casting aluminum alloy, the coarse primary Si and the long needle-rich Fe phase will split the alloy matrix. It is proved that semi-solid treatment can refine the primary phase and improve the morphology of the alloy effectively. In order to improve the mechanical properties of AI-23Si-4.5Fe-3Cu-1Mg alloy, semi-solid slurry of AI-23Si-4.5Fe-3Cu-1Mg alloy was prepared by rod-induced nucleation method. The effect of different process parameters on the microstructure of the alloy was studied, and the changes of the microstructure of the alloy under the condition of semi-solid die-casting were analyzed. The experimental results show that the rod-induced nucleation method can effectively improve the microstructure of the alloy. Not only the primary Si in the alloy can be refined, but also the Fe-rich phase in the alloy structure can be refined obviously, and the eutectic phase and other phases in the microstructure can also be affected accordingly. The effect of rod-induced nucleation on the microstructure of the alloy is different. When the rotating speed of the alloy changes, the moving state of the melt will change. When the rotational speed is too low, the gravity of the melt plays a major role. The relative velocity of inner and outer layer melt in rotating direction is smaller, the contact area between melt and rotating rod is smaller, the thickness is larger, and the centrifugal force produced by rotating rod plays a major role when the rotational speed is too high. Under the influence of centrifugal force, melt will get rid of the rotating rod prematurely. Although the relative velocity of melt inside and outside layer is larger, the contact area between melt and rotating rod in the vertical direction decreases. The contact area between melt and rotor decreases at high rotational speed, and the copper rod with high thermal conductivity can take more heat away from the melt at the same time. The nucleation effect is better than that of steel bars. When the pouring temperature is too high, the residual heat in the slurry is more, the density of free crystal nucleus in semi-solid slurry is reduced, and the composition is supercooled to promote the grain growth. The grain formed in the melt will remelt, reduce the density of free nucleus in the melt, and eventually grow into large grain. The results show that the 蠁 75mm copper bar is used. When the rotating speed of the alloy is 600 r / min and the pouring temperature is 830 鈩，

本文编号：1429599