INFLUENCE OF THE Al CONTENT ON THE PHASE TRANSFORMATIONS IN Cu-Al-Ag ALLOYS

The literature about alloys of the Cu-Al system is extensive, due to its practical use. These alloys are of low cost and present good strength and hardness, depending on the Al content. They are used for making sleeves, guides, seats, flanges, gear wheels and many other critical small parts, as electrolysis cell cathodes, circuit plates and casting moulds when high thermal conductivity is needed. Cu-Al alloys with concentration in the range from 9 to 14wt.%Al contain in their structure the (α + γ1) eutectoid, which is formed through decomposition of the β phase. On rapid cooling from high temperatures, the β phase undergoes a martensitic transformation. When quenched from the β state, alloys containing more than about 11wt.%Al first become ordered to the β 1 phase and then transform martensitically to either β 1 ’,(β 1 ’ + γ’) or γ’, depending on the Al content. In alloys with less than 11wt.%Al the β phase transforms to an fcc type of disordered martensite [8]. Silver additions to the Cu-Al alloys increase its hardness [4] and improves the resistance to stress corrosion [1], without changing significantly the plasticity and workability of the alloys. In this work, the influence of the Al content on the phase transformations of Cu-Al-Ag alloys was studied by classical differential thermal analysis (DTA), optical microscopy (OM) and X-ray diffractometry (XRD), and the results were compared with those found in the literature