AZ91D镁合金自孕育法制浆及其半固态成形技术研究

发布时间：2018-03-23 23:35

  本文选题：自孕育法　切入点：半固态　出处：《兰州理工大学》2010年硕士论文

【摘要】： 孕育处理作为有效细化晶粒的方法被广泛使用,同时合金组织细化处理是获得优质半固态组织的主要方法之一。要获得优质半固态组织的条件之一就是必须在合金熔体中产生足够多的初始晶核,初始晶核在后期会演化出细小的半固态固相颗粒,因此希望初始晶核尽量细小和充足。 本文自主开发了一种能够高效率制备优质半固态浆料的工艺,即自孕育铸造法(Self-inoculation Method,简称SIM)。从晶粒来源和晶粒生长两个角度入手,深入研究了树枝晶破碎球化技术、控制形核抑制树枝晶生长技术,探讨了SIM条件下初生固相的形态演变过程和球晶组织形成机理；系统研究了工艺参数(处理温度、孕育剂加入量和导流器倾角)对AZ91D镁合金半固态组织的影响规律；对不同成形工艺制备的AZ91D镁合金铸坯部分重熔组织进行了初步研究,并在此基础上对AZ91D镁合金流变压铸和触变压铸进行了试验研究。实验结果表明： 1.自孕育剂在自孕育法中作用至关重要,在自孕育剂选择上,应尽量选取组织细小均匀,具有非枝晶组织的孕育剂；在孕育剂加入量上应选取5-8%(质量分数)。 2.在SIM工艺中,只要处理温度(650-680℃)、孕育剂加入量(5-8%,质量分数)和导流器倾角能够良好地匹配,使出口温度接近合金液相线温度,便可以获得优良的半固态浆料。当导流器角度和孕育剂加入量均在有效范围内时,随着处理温度的降低,初生α-Mg经历了由粗大树枝晶→细小块状晶或近球形晶的演变过程。 3.半固态浆料在导流器出口组织细小均匀,水淬后检测其平均颗粒大小为36μm。在压射充型速度在2 m/s,经5-10min保温,温度为585℃的AZ91D镁合金半固态浆料能顺利进行流变压铸,在此工艺范围内,晶粒平均尺寸为60-70μm且固相颗粒中无液相夹裹。压铸件的抗拉强度和硬度分别为185MPa和HV30=67.88。 4.采用自孕育法制备坯料触变性良好,二次重熔后组织细小圆整,且从中心区域到边缘区域晶粒大小均匀；大尺寸(Φ75mm)坯料在585℃保温110min后采用与流变压铸工艺相同的参数进行触变压铸,初生相平均晶粒尺寸为80-90μm,固相率为58%。此时压铸件的抗拉强度和硬度分别为192MPa和HV30=68.74。
[Abstract]:Inoculation treatment is widely used as an effective method for grain refinement. At the same time, the refinement of alloy microstructure is one of the main methods to obtain high quality semi-solid microstructure. One of the conditions for obtaining high quality semi-solid microstructure is to produce enough initial nuclei in the alloy melt. The initial nucleus will evolve into fine semisolid solid particles at the later stage, so it is hoped that the initial nucleus will be as small and sufficient as possible. In this paper, we have developed a process of producing high quality semisolid slurry with high efficiency, that is, self-inoculation method by self-inoculation method. The spheroidization technology of dendritic fragmentation has been studied from the point of view of grain origin and grain growth. The technology of controlling nucleation to inhibit dendritic growth, the morphological evolution process of primary solid phase and the formation mechanism of spherulite structure under SIM were discussed, and the process parameters (treatment temperature, temperature, temperature) were studied systematically. The effect of inoculant addition and diversion angle on the semi-solid microstructure of AZ91D magnesium alloy was studied, and the partial remelting structure of AZ91D magnesium alloy billet prepared by different forming processes was studied. On this basis, rheological die-casting and thixotropic die-casting of AZ91D magnesium alloy were studied. 1. The self-inoculant plays an important role in the self-inoculation method. In the selection of self-inoculant, the inoculant with fine and uniform microstructure with non-dendritic structure should be selected as far as possible, and 5-8% (mass fraction) should be selected in the amount of inoculant. 2. In SIM process, as long as the treatment temperature is 650-680 鈩，

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