Unveiling micromechanism of Fe minor addition‐induced property degradation of an Al‐5.1Cu‐0.65 Mg‐0.8Mn (wt%) alloy

In this paper, the property degradation micromechanism of Al-5.10Cu-0.65 Mg-0.8Mn (wt%) alloy induced by 0.5 wt% Fe minor addition was revealed by atomic-scale scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy coupled with first-principles calculations. The results show that the Fe minor addition to the Al-Cu-Mg-Mn alloy leads to a slight reduction of grain size and the formation of coarse Al₇Cu₂Fe constituent particles. Fe tends to segregate into the T-phase dispersoids, θ'-, and S-phase precipitates by preferentially occupying Cu or Mn sites in these phase structures. The apparent Fe segregation contributes to an increase in stiffness of the T-phase and S-phase but decreased stiffness of the θ' phase. Formation of the coarse Al₇Cu₂Fe constituent particles and decreased stiffness of main precipitates θ' containing Fe result in the degraded strength of the Al-Cu-Mg-Mn-Fe alloy. Further study reveals that corrosion resistance degradation of the Al-Cu-Mg-Mn-Fe alloy is associated with the increased width of precipitation free zones and consecutive grain boundary precipitates. The obtained results have significant implications for the usage of recycled Al alloys and the potential design strategies of high-performance alloys containing Fe.

本文通过原子尺度扫描透射电子显微镜和能量色散X射线光谱结合第一性原理计算，揭示了0.5 wt% Fe微量添加引起的Al-5.10Cu-0.65Mg-0.8Mn（wt%）合金性能退化的微观机制。结果表明，在Al-Cu-Mg-Mn合金中微量添加Fe会导致晶粒尺寸略有减小，并形成粗大的Al₇Cu₂Fe组分颗粒。Fe倾向于通过优先占据T相分散体、θ'-和S相沉淀物这些相结构中的Cu或Mn位点，形成富Fe相。明显的铁偏析导致T相和S相刚度增加，但θ'相刚度降低。粗大的Al₇Cu₂Fe组分颗粒的形成和含Fe的主要沉淀物θ'刚度的降低导致Al-Cu-Mg-Mn-Fe合金的强度降低。进一步的研究表明，Al-Cu-Mg-Mn-Fe合金的耐腐蚀性退化与晶界无沉淀析出带宽度和连续晶界沉淀物的增加有关。所获得的结果对回收铝合金的使用和含铁高性能合金的潜在设计策略具有重要意义。