采用显微硬度测试、HRTEM和原子探针层析技术(APT)等测试手段分析了核元件燃料包壳备选材料LT24铝合金在180 ℃人工时效早期显微硬度、组织变化及析出序列中析出物的Mg与Si原子比(ρ). 结果表明, 在180 ℃时效初期, 合金的硬度显著增加, 析出高数量密度的溶质原子团簇和球状Guinier-Preston (GP)区; 时效4 h后达到硬度峰值, 析出物以高数量密度的针状β"相为主; 进一步时效, 合金处于一硬度平台, 析出物仍以β"相为主. 随时效时间的延长, 析出相逐渐长大, ρ逐渐增加, β"相中ρ在1.23~1.35之间, β"相对合金的强化起最重要作用. 在早期时效过程中合金析出物的析出序列为过饱和固溶体→溶质原子团簇→溶质原子团簇+GP区→溶质原子团簇+GP区+β"相.

The microstructure evolution, atomic ratio (ρ) of Mg and Si in different precipitates, and precipitation strengthening effects during the ageing process were investigated by HRTEM, atom probe tomography (APT) and hardness testing in LT24 aluminum alloy used for nuclear fuel cladding alternative materials. The results show that the early stage of ageing at 180 ℃ led to a significantly increasing of hardness and the formation of high density of solute clusters and Guinier-Preston (GP) zones in the alloy. The alloy reaches peak hardness after ageing at 180 ℃ for 4 h due to a significant increasing density of the β" precipitates. After the peak hardness, a hardness plateau is maintained for longer ageing time, because of the β" precipitate is still the main strengthening phase in the specimens. The precipitates grow larger and the ρ increases with the increasing of ageing time. The ρ in β" needles changes from 1.23 to 1.35. β" needles are the main precipitation strengthening phase of the alloy. The precipitation sequence during the early ageing treatment in alloy can be described as follows: supersaturated solid solution →solute atom clusters→solute atom clusters+GP zone→solute atom clusters+GP zone+β".