Structure of Liquid Aluminium-Copper Alloys

EARLIER work' done in these laboratories has established the existence of copper-rich clusters in the liquid aluminium copper alloys. It was decided to investigate
the behaviour of these clusters at various temperatures
in aluminium-copper alloys because of the great commer-cial and scientific interest, in age-hardening alloys. Such an understanding would be of help in forming it physical picture of the early stages of the precipita-
tion processes. The existence of the clusters is thermo-dynamically possible as it lowers the free energy of the system by increasing the entropy of mixing, The aluminium-rich or copper-rich clusters in liquid aluminium-copper alloys arise because of the negative heat of solution.
The density of the copperrich clusters is greater than that of the parent liquid and the difference in the den-sity could be magnified several times by centrifuging the molten alloy, thus causing the heavier copper-rich clus-ters to move away from the radius of rotation. Conditions are thus created which divide the liquid into aluminium-rich and copperrich portions.