The aluminium - copper - gold ternary system

Despite Au, Al and Cu being individually very wellknown elements, their ternary phase diagram has not been studied in as much detail as those of many other Au-containing ternaries. Here we review what is known, and consider the prospects for technological exploitation of some of the ternary compositions. The components of greatest interest in Al-Au-Cu may be the β-phases, at least two of which have shape memory properties. Of these, ‘Spangold’, which has the nominal stoichiometry Au 7 Cu 5 Al 4 , has received some attention for jewellery applications, while the edge compound Cu 3 Al is a well-known shape memory composition with corresponding specialised industrial uses. The properties of other β-phase compositions in the system have been scarcely investigated. The system also contains an extensive g-phase, Al 4 Au x Cu 9-x , where x ranges from 0 to ~6.5, and the purple gold phase AuAl 2 .