电磁场作用下稀土元素扩散效应对半固态A356铝合金凝固组织的影响

发布时间：2018-01-13 12:48

本文关键词：电磁场作用下稀土元素扩散效应对半固态A356铝合金凝固组织的影响　出处：《江西理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：半固态成形工艺(Semi-Solid Metal Forming),简称SSM,是指金属在凝固过程中,在金属固-液两相区内,通过各种制浆方法,将金属在凝固过程中形成的树枝状晶打碎,然后直接铸造或先半固态铸造,后重熔触变,获得具有一定球状的颗粒状组织,这种方法称为半固态成形方法。通过这种方式获得的铸锭与传统铸造相比有诸多优势,比如能使铸件内部组织致密,气孔少,偏析少,可形成复杂件,零件的力学性能提高等。本研究是以A356铝合金为基体原料,通过施加电磁搅拌和添加微量稀土元素,探究在电磁场作用下稀土添加量对半固态A356铝合金初生α相的影响,以及电磁搅拌及频率对初生α相的影响机理和对稀土Ce在晶内和晶界和不同径向上的分布规律的影响。本文选择Ce和Yb两种稀土元素来探讨在电磁搅拌作用下稀土的最佳加入量,其加入量分别为0.2%、0.4%、0.6%和0.8%Ce以及0.3%、0.5%、0.7%和0.9%Yb,分析了细化剂的细化机理是能否与基体晶粒形成共格关系,以及定量分析了最佳的稀土添加量的原因是与固-液界面前沿的成分过冷度有关,得出了在低过热度浇注,搅拌频率30Hz,15s的情况下,最佳的稀土Ce和Yb的添加量为0.4%和0.7%Yb。在最佳的稀土Ce添加量的情况下,选择10Hz、20Hz、30Hz和40Hz四个搅拌频率来探究其对半固态A356铝合金初生α相和稀土元素在晶内和晶界上的分布的影响,得出了在低过热度浇注下,在搅拌频率为30Hz时初生α相最圆整和细小,其平均形状因子和等级圆直径分别为0.8和76.1μm,分析了频率对组织和稀土Ce分布的影响,频率过高或过低,都不利于熔体的扰动和溶质原子的扩散,降低搅拌效果,使溶质原子产生微观偏聚。在利用30Hz的搅拌频率,添加1.0%、1.4%、1.8%和2.2%Ce的情况下,对比了有无电磁搅拌,探究稀土元素及其化合物在铸锭径向上的存在形态和分布规律,得出了添加较多的稀土元素,稀土在A356铝合金中呈针状,且比较杂乱无序,有电磁搅拌时稀土分布稍加均匀,且在铸锭上的分布从中心到外围逐渐增大,在铸锭半径60%处达到最大值,之后又开始下降,而无电磁搅拌时,稀土分布无规律性,有较明显的偏聚产生。
[Abstract]:Semi-Solid Metal forming process (SSM) means that the metal is in the solid-liquid two-phase region during the solidification process. Through various pulping methods, the dendritic grains formed in the solidification process of the metal were smashed, then cast directly or cast semi-solid first, then remelted and thixoed, and the granular structure with certain spherical shape was obtained. This method is called semisolid forming. Compared with traditional casting, the ingot obtained by this method has many advantages, such as compact internal structure, less porosity, less segregation, and can form complex parts. In this study, A356 aluminum alloy was used as the base material, by applying electromagnetic stirring and adding trace rare earth elements. The effect of rare earth addition on the primary 伪 phase of semisolid A356 aluminum alloy under the action of electromagnetic field was investigated. The influence mechanism of electromagnetic stirring and frequency on the primary 伪 phase and the distribution of rare earth ce in crystal, grain boundary and different radial direction are also discussed. In this paper, two rare earth elements ce and Yb are selected to study electromagnetic stirring. Use the optimum amount of rare earth. The amount of addition was 0.20.40% and 0.8% and 0.3B, respectively, and the amount of 0.30% and 0.9Yb was 0.7% and 0.9Yb, respectively. The refining mechanism of the refiner is analyzed whether it is coherent with the matrix grain, and the reason of the optimum addition of rare earth is related to the component undercooling at the front of the solid-liquid interface. The results show that under the condition of low superheat pouring and stirring frequency 30Hz / 15s. The optimum amount of rare earth ce and Yb was 0.4% and 0.7Yb.The optimum amount of rare earth ce was 10Hz. The effects of four stirring frequencies of 30Hz and 40Hz on the distribution of primary 伪 phase and rare earth elements in semisolid A356 aluminum alloy were investigated. When stirring frequency is 30 Hz, the primary 伪 phase is the most round and fine, its average shape factor and grade circle diameter are 0.8 and 76.1 渭 m, respectively. The influence of frequency on the distribution of rare earth ce and microstructure is analyzed. If the frequency is too high or too low, it will be unfavorable to the disturbance of melt and diffusion of solute atoms, reduce the agitation effect and make the solute atoms to produce micro-segregation. At the stirring frequency of 30 Hz, 1.0% 1.0% of solute atoms are added. In the case of 1.8% and 2.2, the existence and distribution of rare earth elements and their compounds in the radial direction of ingot were studied by comparing the presence and absence of electromagnetic stirring, and the addition of more rare earth elements was obtained. Rare earth in A356 aluminum alloy is needle-like and disorderly. The distribution of rare earth is a little more uniform when electromagnetic stirring occurs, and the distribution on the ingot increases gradually from the center to the periphery. When the radius of the ingot reaches the maximum at 60%, then it begins to decrease, but without electromagnetic stirring, the distribution of rare earth is irregular and the segregation of rare earth is obvious.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG292

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