AN ELECTRON-MICROSCOPE STUDY OF GP ZONES AND THETA'-PHASE IN AL-1.6 AT PERCENT-CU CRYSTALS

Various types of G. P. zones and theta'-phase are formed by aging in Al-1.6 at%Cu crystals. Formation processes of these structures have been investigated by high resolution electron microscopy with the following results: (a) Three-dimensional Cu-atom clusters are formed at the beginning of aging at both 373 and 423 K, respectively. (b) In 373 K aging, these clusters change to G.P.-1 zones and/or G.P.-2(3) zones whose Cu-rich planes are separated with three Al-rich planes. Multi-layered G.P.-2(3) zones and sometimes multi-layered G.P.-2(2) zones whose Cu-rich planes are separated with two Al-rich planes are formed by further aging at 373 K. (c) In 423 K aging, the Cu-atom clusters change to G.P.-2(2) zones, and followed by the formation of multi-layered G.P.-2(2) zones. Theta'-phase is formed within the multi-layered G.P.-2(2) zone by electron irradiation induced diffusion at room temperature in the same way as in aging at 523 K.