STRENGTHENING EFFECTS OF MICROSTRUCTURE EVOLUTION DURING EARLY AGEING PROCESS IN Al-Mg-Si ALLOY
WANG Bo, WANG Xiaojiao, SONG Hui, YAN Jujie, QIU Tao, LIU Wenqing, LI Hui()
Key Laboratory for Microstructures, Shanghai University, Shanghai 200444
Cite this article:
WANG Bo, WANG Xiaojiao, SONG Hui, YAN Jujie, QIU Tao, LIU Wenqing, LI Hui. STRENGTHENING EFFECTS OF MICROSTRUCTURE EVOLUTION DURING EARLY AGEING PROCESS IN Al-Mg-Si ALLOY. Acta Metall Sin, 2014, 50(6): 685-690.
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".
Fund: Supported by National Natural Science Foundation of China (No.51301103), China Postdoctoral Science Foundation (No.2013M541507), Key Project of Shanghai Science and Techology Commission (No.12JC1404000) and Innovation Fund of Shanghai University
Fig.1 Hardness of Al-Mg-Si alloy aged at 180 ℃ for different times after solution annealing at 550 ℃ for 1 h
Fig.2 Bright-field TEM images of Al-Mg-Si alloy aged at 180 ℃ for 5 min (a) and 4 h (b) (Insets show the corresponding SAED patterns)
Fig.3 Three dimensional distributions of Mg, Si and Cu atoms in Al-Mg-Si alloy aged at 180 ℃ for 5 min (80 nm×80 nm×150 nm) (a), 30 min (68 nm×68 nm×465 nm) (b), 4 h (80 nm×80 nm×200 nm) (c) and 8 h (60 nm×60 nm×240 nm) (d)
Fig.4 Evolution of number density of precipitates in Al-Mg-Si alloy aged at 180 ℃ for different times
Fig.5 Fig.5 Evolution of atomic ratio of Mg and Si (ρ) in solute clusters, GP zones and β" phase in the specimens aged at 180 ℃
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