Ageing processes and age-hardening characteristics of Al-Ag-Cu ternary alloys were investigated by means of measuring hardness and specific heat. It was confirmed by measuring specific heat that two kinds of G. P. zones were formed on ageing at low temperatures; the one was rich in silver and the other was in copper. The formation of the former zones preceeded that of the latter. An intermediate phase predominantly precipitated on ageing above 190°C.
Marked hardenability on ageing was observed, which proved that Al-Ag-Cu alloys are one of the strongest Al-base alloys. Solid solution hardening behavior was also studied and it was concluded that this behaviour could not be explained only by the strain field produced by the solute atoms.