COMPUTATIONAL SIMULATION |
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Quench Sensitivity and Phase Transformation Kinetics of LD7 Aluminum Alloy |
JIANG Dao1,2, YI Youping1,2, HUANG Shiquan1
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1 State Key Laboratory of High Performance Complex Manufacturing, Central South University, Changsha 410083; 2 Light Alloy Research Institute, Central South University, Changsha 410083 |
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Abstract The quench sensitivity of LD7 aluminum alloy was determined by the time-temperature-transformation (TTT) curves and time-temperature-property (TTP) curves by an interrupted quench technique with measurement of as-quenched electro-conductivity and as-aged hardness.The microstructure evolution and phase transformation kinetics during isothermal quenching treatment were studied by the transmission electron microscopy (TEM) and Johnson-Mehl-Avrami (JMA) equation. The results showed that the nose temperature of TTT curves and TTP curves were both about 350 ℃, and the incubation period was about 2 s, with the quench sensitivity range of 290-410 ℃. The supersaturated solid solution decomposed and particles precipitate during quench process; the precipitation rate was the highest at the nose temperature. Prolonging holding time leads to bigger and coarser second phase particles and widened precipitation free zone in the matrix, more spaced second phase particles precipitated at the grain boundary, which resulted in the loss of solutes and decrease of subsequent aging hardening effect. The fitted S-curve according to the phase transformation kinetics equation explained that the precipitation rate was the highest at about 350 ℃ and the mechanism of solid solution mainly precipitates as needle-like phases during quench sensitive range.
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Published: 25 June 2017
Online: 2018-05-08
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