The modified crystallography of tin in Al-Cu-Sn

The crystallographic identity of tin particles formed during the early stages of solid solution decomposition in an Al-1.7at.%Cu-0.01at.%Sn alloy has been investigated by high resolution transmission electron microscopy. It was found that in association with Cu-rich precipitates (GP zones or theta') having just nucleated, tin favours an orientation relationship relative to the aluminium matrix that is distinctly different from that observed in the binary alloy Al-0.01at.%Sn. This observation implies that the presence of copper modifies the preferred crystallographic identity of tin particles in Al-Cu-Sn. Three-dimensional atom probe microscopy confirms that tin and copper solute clusters interact before precipitation of the crystalline phases.