2005 年 46 巻 2 号 p. 241-250
In order to improve fundamental understanding of the ageing behaviour in Al-Mg(-Ag) alloys, the effects of trace additions of Ag on the precipitate microstructures of the Al-Mg alloys aged at temperature range 20 and 90°C was examined.
The fine-scale and uniformly distributed spheroidal precipitate particles were formed in the ternary Al-10Mg-0.5Ag (mass%) alloy during the natural ageing process of periods of 16 months, while no precipitate particles were observed in the binary Al-10 mass% Mg alloy under the same ageing conditions. These fine scale, spheroidal precipitate particles observed in the ternary Al-10Mg-0.5Ag (mass%) alloy were identified as the β″ phase which has the ordered L12 structure with the lattice parameter of a=0.408 nm. The orientation relationship between the β″ phase and the aluminium matrix was of the form: (100)L12||(100)α, [001]L12||[001]α. The spheroidal precipitate particles having the ordered L12 structure in the Ag-modified alloys were unstable when the specimen was aged at 90°C.
The plate-like precipitate particles were formed in binary alloys aged from 30 days at 90°C. The plate-like particles had habit planes of {100}α, and were identified as the β′ phase which is consistent with the metastable β′ phase (Al3Mg2, a=1.002 nm, c=1.636 nm) in Al-Mg alloys.
