A phenomenon that Al-6.0%Zn-0.75%Mg alloy sheets furnace-cooled after solution heat treatment had higher strength than water-quenched sheets under specific aging condition was reported. However, the strengthening mechanism related to furnace-cooling had been not clarified yet. In this research, replication test of the strengthening phenomenon of furnace-cooled sheets and the microstructural change during natural aging and artificial aging at 200°C after furnace-cooling after solution heat treatment was investigated by tensile tests, SAXS measurements, STEM observation and electrical conductivity measurement. The strengthen phenomenon of furnace-cooled sheets was reproduced. In as-furnace-cooled sheets, 2-5 nm clusters which induced lattice strain were observed in LAADF-STEM image apart from atomic number contrast in HAADF-STEM image. The clusters seemed to be generated during furnace cooling. The clusters seemed to cause suppression of reversion and promotion of age hardening in furnace-cooled material.
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Aisu et al. (2023) studied this question.
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