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Processing of magnesium alloys with ultrafine grain structure.

机译：具有超细晶粒结构的镁合金的加工。

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摘要

The relationship between processing, structure and properties is analyzed in magnesium alloys subjected to equal-channel angular pressing.;Finite element modeling is used to show that the flow softening behavior associated with grain refinement might cause shear localization and billet failure in magnesium alloys processed by ECAP. It also shows that increasing the angle between the channels of the die reduces the accumulated damage in the billets and increasing the material strain rate sensitivity reduces the tendency for shear localization. Both procedures reduce the tendency for billet cracking.;The mechanism of grain refinement in magnesium alloys deformed at moderate temperatures differs from that observed in other metals such as copper and aluminum. Fine grains nucleate along pre-existing grain boundaries in a necklace pattern in coarse-grained magnesium while homogeneous nucleation of fine grains is observed in fine-grained. A bimodal grain size distribution is observed after processing alloys from an initial coarse structure and a homogeneous distribution of ultrafine grains is the outcome of a starting fine one.;Experiments and simulations are used to analyze the evolution of texture. It is shown that different components are formed depending on the activity ratio of non-basal slip and processing route. The measured pole figures exhibit features characteristic of high activity of non-basal slip. It is also shown that the development of some texture components and their orientation depends on the initial texture and the die angle which provide the basis for future texture engineering.;Excellent superplastic properties, including a record elongation for a magnesium alloy, were observed after ECAP. Systematic research showed that the structure characteristics prior and after ECAP play significant role on these properties. Grain growth during superplastic deformation causes a strain hardening effect. The experimental results showed good agreement with the theoretical model for grain boundary sliding.
机译：分析了等通道角压下镁合金的加工，组织与性能之间的关系。有限元建模表明，细化晶粒的流动软化行为可能会导致镁合金加工后的剪切局部化和坯料破坏。亚太经社会。它还表明，增加模具的通道之间的角度可减少坯料中的累积损伤，而增加材料应变速率敏感性则可降低剪切局部化的趋势。两种方法都降低了钢坯开裂的趋势。在中等温度下变形的镁合金中，晶粒细化的机理不同于在其他金属（如铜和铝）中观察到的细化机理。在粗粒镁中，细晶粒以项链形式沿先前存在的晶界成核，而在细粒中观察到细晶粒的均匀成核。从初始的粗组织加工合金后，观察到双峰晶粒尺寸分布，而超细晶粒的均匀分布是开始的精细晶粒的结果。；使用实验和模拟来分析织构的演变。结果表明，根据非基层泥浆的活度比和加工路线，会形成不同的组分。测得的极图显示出非基层滑移高活动性的特征。研究还表明，某些织构成分及其取向的发展取决于初始织构和模具角，这为将来的织构工程提供了基础。; ECAP后观察到优异的超塑性，包括创纪录的镁合金伸长率。系统研究表明，ECAP前后的结构特征对这些特性起着重要作用。超塑性变形过程中的晶粒长大会引起应变硬化效应。实验结果与晶界滑动理论模型吻合良好。

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  • 作者

    Figueiredo, Roberto Braga.;

  • 作者单位

    University of Southern California.;

  • 授予单位 University of Southern California.;
  • 学科 Engineering Mechanical.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 140 p.
  • 总页数 140
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;工程材料学;
  • 关键词

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