The mechanisms of abnormal grain growth (AGG) in particle-containing systems have long been a mystery. Recently, we reported that a non-random particle distribution can induce a grain size advantage and trigger AGG. However, the processing conditions leading to a non-random particle distribution are far from being understood. Here, we investigate the particle distribution and concomitant grain growth behavior at different annealing temperatures and times in an Al-3.5 wt pct Cu alloy by scanning electron microscopy (SEM). At high temperatures and long times, the particle distribution evolves from random to non-random, with an accompanying transition from normal grain growth (NGG) to AGG. Analytical calculations suggest that a non-random particle distribution is introduced by residual Cu segregation even after homogenization. In short, the corresponding fluctuation of θ-Al₂Cu phase distribution is amplified at elevated temperatures via particle dissolution. We quantify the spatial inhomogeneity of particles through the Gini coefficient and link this important parameter to the critical grain size necessary for AGG. The trends are conveyed succinctly in a temperature–time–(structural) transformation (TTT) diagram, which identifies the onset of AGG in an Al-3.5 wt pct Cu alloy.

长期以来，含颗粒系统中异常晶粒生长（AGG）的机理一直是个谜。最近，我们报道了非随机的颗粒分布可以诱导晶粒尺寸优势并触发AGG。然而，导致非随机颗粒分布的加工条件还远远不能被理解。在这里，我们通过扫描电子显微镜（SEM）研究了Al-3.5 wt pct Cu合金在不同退火温度和时间下的颗粒分布和伴随的晶粒生长行为。在高温和长时间下，颗粒分布会从无规演变为非随机，并伴随着从正常晶粒生长（NGG）到AGG的转变。分析计算表明，即使在均质化之后，残余的铜偏析也会引入非随机的颗粒分布。简而言之，θ- Al ₂ Cu相分布在高温下通过颗粒溶解而放大。我们通过基尼系数来量化粒子的空间不均匀性，并将这一重要参数与AGG所需的临界晶粒尺寸联系起来。在温度-时间-（结构）转变（TTT）图中简要地传达了这种趋势，该图确定了Al-3.5 wt％pct Cu合金中AGG的出现。