Thermal Behavior of Cu—Al Alloys Near the α-Cu—Al Solubility Limit

Abstract

The thermal behavior of Cu—Al alloys with 17, 19 and 21 at.%Al was examined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), X-ray diffractometry (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The presence of the gamma phase (Al₄Cu₉)was clearly detected for the Cu—19 at.%Al alloy and caused the α₂ phase disordering process in two stages. The tendency to increase the α₂ dissolution precipitates with the increase in the Al content seems to be reverted for compositions at about 21 at.%Al and the heating/cooling ratio seems to influence the thermal response of this process. The presence of the endothermic peak corresponding to the β₁→β transformation depends on an incomplete β decomposition reaction. The variation of the heating rate showed that the β₁→(α+γ₁) decomposition is the dominant reaction for alloys containing 19 and 21 at.%Al.