Effects of Co and Zr additions on the thermal behavior of the Cu₈₁Al₁₉ alloy

The thermal behavior of the annealed Cu₈₁Al₁₉ alloy with Co and Zr additions was investigated using differential thermal analysis, differential scanning calorimetry, electrical resistivity measurements, optical microscopy, scanning electron microscopy, Vickers microhardness, and X-ray diffractometry. The results showed that the Co addition slightly increased the critical temperatures of melting and solidification of the Cu₈₁Al₁₉ alloy, suppressed the eutectoid reaction and the β phase ordering, and introduced a new route for the α₂ phase disordering. A mechanism to this phenomenon is suggested in the present work. On the other hand, the Zr addition did not significantly alter the critical temperatures of melting and solidification of the Cu₈₁Al₁₉ alloy, decreased the intensity of the eutectoid reaction, and increased the α₂ phase disordering rate and the β phase decomposition. Besides that, it introduced a new thermal event at higher temperatures, related to the dissolution of precipitates with Al. Both Zr and Co additions increased the electrical resistivity and the microhardness of the Cu₈₁Al₁₉ alloy due to the precipitation of intermetallic compounds.