Structure of Age-Hardened Aluminium-Copper Alloys

Abstract

WE have made X-ray diagrams of aluminium-copper alloys (5 per cent Cu) age-hardened at various temperatures (25°–200° C.) ; the samples were composed of large crystals, and the radiation was made monochromatic by reflection by a crystal. In a previous paper¹, we described a new phenomenon which appeared in these diagrams: streaks of various length issuing from the centre, which we attributed to the reflection of X-rays by planes. We have shown that these planes are parallel with the 100 planes of the crystal of solid solution and, moreover, that they are of small dimensions (100–400 A.). We assumed, therefore, that these planes were composed of groups of copper atoms, without making any hypothesis about the disposition of the atoms within those groups.