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The inhomogeneous microstructure and deformation of similar and dissimilar Al-Zn containing Mg friction stir welds

机译：相似和相异的含铝镁合金搅拌摩擦焊缝的不均匀组织和变形

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摘要

The magnesium-based aluminum-zinc alloys have excellent stiffness to weight ratios, and may be combined by friction stir welding to expand the possible applications. The high aluminum alloy AZ80 in particular has the advantage of being relatively stiff but still extrudable. However limited friction stir welding research is available for this alloy and extrapolation from the extensive work in aluminum alloys is impractical due differences in precipitation behaviour, and magnesium's high plastic anisotropy and tendency to form strong textures during friction stir welding.;This work investigates the correlations between local friction stir welded microstructures, textures, residual strains, and the local deformation behaviour based on strain mapping during tensile tests. Covering bead-on-plate and butt configurations, joining of similar and dissimilar materials, and a range of processing conditions, many findings of interest for deformation modelling and industrial applications are presented.;Synchrotron x-ray diffraction study of an entire friction stir weld was used to determine texture, residual strain and dislocation density data from a single experiment. A number of unique findings were made, mainly related to the asymmetric distribution of properties both between sides of the weld and through the depth. Particularly in the case of strain measurements, features not detectable at coarser measurement spacing or by line scan are presented and compared for multiple processing conditions.;Investigation of the longitudinal material flow during welding showed that even when periodicity in grain size, precipitate distribution, or texture was not observed, periodic changes in texture intensity resulting from compaction of material behind the tool were present, providing evidence that movement of nugget material remained periodic.;Strain localisation and fracture behaviour were found to be completely different between good quality similar and dissimilar friction stir welds. For similar magnesium friction stir welds, higher heat input was shown to improve mechanical performance by reducing the residual strain, while for dissimilar friction stir welds, deformation behaviour was found to be more sensitive to the final material distribution in the friction stir weld nugget. For dissimilar welds, even minor changes to the material flow were shown to have a major impact on the tensile performance.
机译：镁基铝锌合金具有出色的刚度与重量比，并且可以通过搅拌摩擦焊进行组合以扩大可能的应用范围。高铝合金AZ80特别具有相对坚硬但仍可挤出的优点。然而，对于这种合金的摩擦搅拌焊接研究有限，并且由于析出行为的差异以及铝合金的高塑性各向异性以及在摩擦搅拌焊接过程中形成强织构的趋势，因此在铝合金的大量工作中进行推断是不切实际的。拉伸试验过程中基于应变映射的局部摩擦搅拌焊接组织，组织，残余应变和局部变形行为之间的关系。涵盖了板对焊和对接配置，相似和不相似材料的连接以及一系列加工条件，为变形建模和工业应用提供了许多有趣的发现;整个搅拌摩擦焊缝的同步辐射X射线衍射研究通过一次实验，我们就可以用它来确定织构，残余应变和位错密度数据。做出了许多独特的发现，主要与焊缝两侧之间以及整个深度之间的特性不对称分布有关。特别是在应变测量的情况下，提出了在较粗的测量间隔或通过线扫描无法检测到的特征，并针对多种加工条件进行了比较。;对焊接过程中纵向材料流动的调查表明，即使晶粒尺寸，沉淀物分布周期性或没有观察到织构，存在由于工具后部材料压紧而导致的织构强度的周期性变化，这表明金块材料的运动保持周期性。证据表明，在质量相似和相异的摩擦之间，应变局部化和断裂行为是完全不同的搅拌焊缝。对于相似的镁合金搅拌摩擦焊缝，显示出更高的热量输入可通过减少残余应变来改善机械性能，而对于不相似的摩擦合金搅拌焊缝，发现变形行为对摩擦合金搅拌焊核中的最终材料分布更加敏感。对于不相似的焊缝，即使是很小的材料流量变化也显示出对拉伸性能的重大影响。

著录项

  • 作者

    Hiscocks, Jessica.;

  • 作者单位

    Queen's University (Canada).;

  • 授予单位 Queen's University (Canada).;
  • 学科 Materials science.
  • 学位 Ph.D.
  • 年度 2018
  • 页码 234 p.
  • 总页数 234
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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