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<p>Abnormal grain growth (AGG) during subsequent temper condition is one of the challenges associated with the friction stir processed (FSP) Al alloys, as it leads to substantial microstructural inhomogeneity and thus inferior mechanical properties. The mechanisms governing AGG in FSP Al alloys and the reasons behind the suppression of AGG <i>via</i> pre-strain rolling still remain elusive. In the present study, AA2198 (Al–3.2Cu–1.0Li–0.3&#xa0;Mg–0.4Ag–0.1Zr) alloy subjected to FSP was used for a systematic study by linking AGG with secondary particles, mechanisms, and morphological evolution. The as-FSP samples were cold rolled to a 20&#xa0;pct reduction in thickness (pre-strained condition). The samples in both as-FSP and pre-strained conditions were solution treated for 1&#xa0;hour at 510&#xa0;°C and were subsequently characterized in detail to examine the microstructural evolution. As anticipated, the as-FSP samples showed substantial AGG; however, no AGG was observed in the pre-strained samples. The study reveals that the soluble particles are ineffective in pinning down the grain boundaries, and insoluble dispersoids effectively govern the AGG. The governing mechanism is found to be the grain boundary mobility advantage, and it leads to a unique morphological signature containing large irregular AGG grains and island matrix grains. It is noted that the growth advantage arises <i>via</i> anisotropy in grain boundary mobilities and insufficient volume fraction of dispersoids. The mechanism of grain boundary mobility advantage and the reasons behind its suppression in AA2198 alloy are discussed in detail.</p>

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Abnormal Grain Growth in Friction Stir Processed Al–Cu–Li (AA2198) Alloy: Mechanism and Mitigation

  • 期刊论文

  • 发表日期：

    2025年9月9日

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  • Vishal Shambu,
  • Niraj Nayan,
  • M. J. N. V. Prasad

摘要

Abnormal grain growth (AGG) during subsequent temper condition is one of the challenges associated with the friction stir processed (FSP) Al alloys, as it leads to substantial microstructural inhomogeneity and thus inferior mechanical properties. The mechanisms governing AGG in FSP Al alloys and the reasons behind the suppression of AGG via pre-strain rolling still remain elusive. In the present study, AA2198 (Al–3.2Cu–1.0Li–0.3 Mg–0.4Ag–0.1Zr) alloy subjected to FSP was used for a systematic study by linking AGG with secondary particles, mechanisms, and morphological evolution. The as-FSP samples were cold rolled to a 20 pct reduction in thickness (pre-strained condition). The samples in both as-FSP and pre-strained conditions were solution treated for 1 hour at 510 °C and were subsequently characterized in detail to examine the microstructural evolution. As anticipated, the as-FSP samples showed substantial AGG; however, no AGG was observed in the pre-strained samples. The study reveals that the soluble particles are ineffective in pinning down the grain boundaries, and insoluble dispersoids effectively govern the AGG. The governing mechanism is found to be the grain boundary mobility advantage, and it leads to a unique morphological signature containing large irregular AGG grains and island matrix grains. It is noted that the growth advantage arises via anisotropy in grain boundary mobilities and insufficient volume fraction of dispersoids. The mechanism of grain boundary mobility advantage and the reasons behind its suppression in AA2198 alloy are discussed in detail.