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首页> 外文期刊>Materials Science and Engineering >Microstructural features of intergranular brittle fracture and cold cracking in high strength aluminum alloys
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Microstructural features of intergranular brittle fracture and cold cracking in high strength aluminum alloys

机译：高强度铝合金晶间脆性断裂和冷裂纹的组织特征

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摘要

Intergranular brittle fracture has been mainly observed and reported in steel alloys and precipitation hardened Al-alloys where intergranular precipitates cover a major fraction of the grain boundary area. 7xxx series aluminum alloys suffer from this problem in the as-cast condition when brittle intermetallics cover almost all the interdendritic spaces and grain boundaries. Brittle intermetallics formed during the non-equilibrium solidification upon direct chill (DC) casting provide favorable sites for crack initiation and propagation at different stages of solidification and cooling. Such micro-cracks may propagate rapidly in the presence of residual thermal stresses and lead to catastrophic failure of DC-cast billets that is called ℃old cracking". In this research work fractographic investigations were performed on as-cast AA7050 specimens failed during tensile tests. In-situ tensile tests were also performed using an Environmental Scanning Electron Microscope (ESEM) to follow the propagation path of cracks at critical temperatures. They revealed that the alloy loses its ductility below 300 ℃ and becomes extremely vulnerable to cracking and failure. Comparison of the fracture surfaces of tensile samples with real cracked billets helps to understand the mechanisms of crack formation and catastrophic failure.
机译：主要在钢合金和沉淀硬化的铝合金中观察到并报道了晶间脆性断裂，其中晶间析出物覆盖了大部分晶界区域。当脆性金属间化合物几乎覆盖所有的枝晶间空间和晶界时，7xxx系列铝合金在铸态时会遭受此问题的困扰。在直接冷却（DC）铸造时，在非平衡凝固过程中形成的脆性金属间化合物为凝固和冷却的不同阶段的裂纹萌生和扩展提供了有利的位置。这样的微裂纹在残余热应力的作用下可能迅速传播，并导致铸坯的灾难性破坏，称为“旧裂纹”。在这项研究工作中，对在拉伸试验中失败的铸件AA7050试样进行了分形研究。还使用环境扫描电子显微镜（ESEM）进行了原位拉伸试验，以追踪临界温度下裂纹的传播路径，结果表明该合金在300℃以下会失去延展性，极易出现裂纹和破坏。带有真实开裂坯料的拉伸样品的断裂表面的分布有助于理解裂纹形成和灾难性破坏的机理。

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  • 来源
    《Materials Science and Engineering》 |2010年第8期|1828-1834|共7页
  • 作者

    M. Lalpoor; D.G. Eskin; G. ten Brink; L. Katgerman;

  • 作者单位

    Materials Innovation Institute, MSE, Mekelweg 2,2628 CD Delft, The Netherlands;

    Materials Innovation Institute, MSE, Mekelweg 2,2628 CD Delft, The Netherlands;

    Department of Applied Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands;

    Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, Delft, 2628 CD, The Netherlands;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    DC-casting; aluminum alloys; cold crack; brittle fracture; thermal stress;

    机译：直流铸造;铝合金冷裂纹脆性断裂热应力;

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