Role of C and Fe in Grain Refinement of an AZ63B Magnesium Alloy by Al-C Master Alloy

1. IntroductionMagnesium alloys have been utilized as structural ma-terial replacing other metals and plastics in the electronicand automobile industries because of their light weightand high recyclability. Grain refinement[1~9] is an im-portant method to improve their mechanical propertiesand workability.Mg-Al based alloys are the most common commer-cial magnesium alloys, and grain-refining treatment isgenerally required. Carbon addition[10~17] and Elfinalprocess[18~22] are the two major gra…     

Mg-TiB2中间合金和Sr对AZ91D镁合金显微组织的细化

采用SEM、EDS和XRD等测试手段研究了粉末原位合成法制备的Mg-50%TiB2(质量分数,下同)中间合金的组织和结构,以及Mg-50%TiB2和Sr对AZ91D镁合金显微组织的细化效果。结果表明,1.4%(Mg-50%TiB2)中间合金和0.1%Sr的复合添加可使AZ91D镁合金的α-Mg晶粒尺寸由基体合金的240μm降至49μm。通过面错配度计算证实TiB2可成为初生-αMg的良好异质核心。加入碱土元素Sr引起合金成分过冷度增加,从而激活固/液界面前沿潜在的TiB2核心,提高TiB2的形核率。     

Mg-Al基镁合金晶粒细化的研究进展

综述了添加含碳变质剂,含钛、硼细化剂,碱金属,碳族元素,氮族元素,稀土元素和准晶合金对Mg-Al基镁合金晶粒细化的研究进展,系统讨论了各种细化剂对Mg-Al基镁合金的晶粒细化效果,以及对各种细化剂细化机理的研究,旨在为镁合金晶粒细化研究提供一个参考.     

多向锻造法细化镁合金晶粒的研究现状

多向锻造技术能显著细化晶粒,大幅改善材料的力学性能,是一种极具潜力的大塑性变形工艺。综述了多向锻造技术细化镁合金晶粒的研究现状,介绍了多向锻造技术的工艺流程以及晶粒细化机制,展望了多向锻造技术未来的研究方向。     

Sliding and Migration of Tilt Grain Boundaries in a Mg–Zn–Y Alloy

Sliding and migration of tilt grain boundaries in a Mg–Zn–Y alloy have been investigated on the atomic scale using aberration‐corrected scanning transmission electron microscopy. Grain boundary sliding is accommodated by non‐basal dislocations moving along the grain boundary; grain boundary migration is induced by the motion of grain boundary dislocations with synchronized grain boundary diffusion. Simultaneous sliding and migration of tilt boundaries take place in both Mg matrix and long period stacking ordered phases. These results provide evidence for occurrence of grain boundary motion, which may play a role in plasticity of this kind of Mg alloys.     

Al-Ti-B中间合金元素实收率的控制与细化效果

本文采用氟盐反应法,通过不同粒度的KBF_4、K_2TiF_6原料与Al熔体反应制备出Al-5Ti-1B中间合金,然后分别从元素实收率、微观组织特征、晶粒细化效果等方面讨论了KBF_4、K_2TiF_6粒度对制备Al-5Ti-1B中间合金的影响。实验结果显示,控制KBF_4、K_2TiF_6的粒度可以有效地控制Ti、B元素的实收率、TiAl_3相的尺寸及分布的均匀性,从而起到改善细化效果的作用。该研究结果期望为工业生产高质量Al-Ti-B中间合金细化剂提供技术参考。     

变形镁合金晶粒细化及热处理后的组织和性能

通过变形方法细化晶粒提高镁合金塑性.大挤压比(100:1)可获得细晶镁合金挤压薄板,其晶粒尺寸为2.5-12.5μm;大挤压比+轧制确保合金获得平均晶粒尺寸小于5μm的细晶镁合金薄板.通过优化再结晶退火制度使合金具有最佳的组织结构和良好的力学性能.在523K保温20min后细晶(晶粒尺寸小于12.5μm)镁合金板材具有良好的热拉深性能,能成功拉深出质量完好的筒形件,而晶粒尺寸大于25μm,出现不良的热拉深现象.     

冷却槽对自孕育法制备ZA92镁合金组织的细化作用

采用自孕育法制备新型的ZA92镁合金,研究了冷却槽对组织的细化作用,并对其机理进行了分析。结果表明:合金熔体内部的形核与冷却槽的激冷作用、熔体的流动速度及剪切力的大小有关,合适的冷却槽角度有利于晶粒的游离和增殖。熔体在流经冷却槽的过程中,其组织变化趋势为:粗大枝晶→细小枝晶→等轴晶→蔷薇状晶和近球状晶。冷却槽角度较大或较小均不利于组织的细化,当冷却槽角度在30~45°之间时,坯料组织的晶粒分布比较集中且细小,其平均晶粒尺寸在47.5~51.4μm之间。     

The Effect of Solidification Dynamics on the Formation of the Skin in Die Cast Mg–Al and Mg–RE Alloys

The grain microstructures and hardness of the surface layers of a Mg–RE alloy (3.44 mass % La) and two Mg–Al alloys, (8.77 and 11.6 mass % Al), are compared. All three alloys exhibit a harder surface layer, or skin, with fine primary α (Mg) grains, and a softer core with a larger grain size due to the prevalence of externally solidified grains (ESGs), but the skin of the RE alloy is more continuous and uniform due to the relative absence of ESGs. The distribution of ESGs can be related to the rheology of the liquid–solid mixtures inside the die: the solid fraction in the RE alloy, for given drop in temperature, is much larger than for the Mg–Al alloys. Being more viscous, the liquid in the RE alloy prevents the migration of ESGs towards the surface, hence the more uniform and tightly packed grain microstructure and better defined skin.     

Zr对Al-Li合金晶粒细化作用的电子理论分析

运用固体经验电子理论(EET),对Al-Li-Zr合金的价电子结构进行计算.结果表明:Zr与Al原子存在强烈的相互作用,在固溶体中形成Al-Zr偏聚区.Al-Zr原子的偏聚析出的细小Al3Zr粒子,均匀弥散分布在基体中,起到抑制晶粒长大,细化Al3Li晶粒的作用.Al3Zr和Al3(Zr,Li)粒子具有较强的Al-Zr共价键,不易被位错的切割折断,因而对位错的运动有较大的阻力,对合金起到强化作用.另一方面,共格复合相Al3(Zr,Li)的析出,可以降低共格界面错配度,使得界面键合强度分布较均匀,对提高基体的韧性是有益的.