A356铝合金自孕育流变压铸过程中的凝固行为

发布时间：2018-10-21 12:34

【摘要】：采用自孕育法制备A356铝合金半固态浆料,研究薄壁件流变压铸过程中的凝固行为。结果表明:在自孕育制浆过程中,等温保温过程对初生α(Al)颗粒的尺寸和形貌影响较大,而对后续薄壁件压铸过程中的二次凝固组织影响不是很大。当剩余液相充填型腔时,型腔提供的较大冷却速率使剩余液相爆发形核;晶核的生长分为稳定生长和失稳生长两个过程。爆发形核的核心先稳定生长成球状小颗粒,稳定生长的极限尺寸为6.5μm。由于"成分过冷"等因素的存在,一次凝固(α_1)颗粒和二次凝固(α_2)颗粒最终均出现不稳定生长现象。由于α_1颗粒的存在,剩余液相的成分与原始成分相比更接近共晶成分,导致α_2颗粒中Si的含量较α_1颗粒中的高。α_2颗粒将共晶反应限制在许多晶间小区域内,在较高的局部冷却速率下,共晶硅最终长成细小纤维状或菊花状.
[Abstract]:The semi-solid slurry of A356 aluminum alloy was prepared by self-inoculation method, and the solidification behavior of thin wall parts during rheological die casting was studied. The results show that in the process of self-inoculating pulping, the isothermal holding process has a great effect on the size and morphology of the primary 伪 (Al) particles, but not on the secondary solidification structure of the subsequent thin-walled parts during die-casting. When the residual liquid phase fills the cavity, the large cooling rate provided by the cavity makes the residual liquid phase burst nucleation, and the growth of the crystal nucleus can be divided into two processes: stable growth and unstable growth. The core of explosive nucleation first grows stably into globular particles, and the limit size of stable growth is 6.5 渭 m. Due to the existence of "composition undercooling" and other factors, both the primary solidification (伪 _ 1) particles and the secondary solidification (伪 _ 2) particles eventually appear unstable growth phenomenon. Because of the presence of 伪 _ 1 particles, the composition of the residual liquid phase is closer to the eutectic composition than the original composition, resulting in the higher Si content in 伪 _ 2 particles than in the 伪 _ 1 particles. 伪 _ 2 particles limit the eutectic reactions to many small intergranular regions. At higher local cooling rate, eutectic silicon eventually grows into fine fibrous or chrysanthemum.
【作者单位】：兰州理工大学省部共建有色金属先进加工与再利用国家重点实验室;兰州理工大学有色金属合金及加工教育部重点实验室;
【基金】：国家自然科学基金资助项目(51464031)~~
【分类号】：TG292

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