Abstract
The influence of quenching temperature on the formation of G.P.zones and on the pre-transition (or fluctuation) in Al-1.28 wt%Cu and −3.82 wt%Cu has been investigated by measuring the changes of electrical resistivity and by taking X-ray Laue photographs and electron micrographs. Each G.P.zone solvus (TG.P.) of Al-1.28 wt%Cu and −3.82 wt%Cu alloys is 80°C and 190°C respectively. The specimen aged above the TG.P. reaches the “clustered state” (i.e. the state of pre-transition). The fluctuation makes diffuse X-ray scattering along the ⟨110⟩ axis at a higher angle of {311}α spots. G.P.zones in Al-3.82 wt%Cu alloy exhibit a sort of arrow-like weak streaks streching from {311}α spots and θ″ zones in the alloy show needle-like strong streaks extending from the nodes corresponding to the reciprocal spots of the θ″ zones. The electrical resistivity is increased by those θ″ zones formed in the fluctuated state. The facility of the formation and microstructure of G.P.zones on aging seem to be influenced by the quenching temperature. The precipitation sequence is as follows:
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C.V.: the concentration of excess vacancy, D.S.C: the degree of supersaturation of Cu atom, I: G.P.zones shall be able easily to be transformed to θ″ zones, II: Al-1.28 wt%Cu alloy quenched to 0°C water, III: Al-3.82 wt%Cu alloy quenched to 200°C oil bath, IV: Al-3.82 wt%Cu alloy quenched to 0°C water.
