Solidifying incongruently melting intermetallic phases as bulk single phases using the example of Al2Cu and Q-phase in the Al–Mg–Cu–Si system

Plane front directional solidification experiments were carried out for preparing incongruently melting intermetallic phases in the quaternary alloy system Al–Cu–Mg–Si, particularly the binary Al2Cu phase and the quaternary phase (“Q-phase”). By this method, bulk samples that consist of only a single phase are generated. Sample sections consisting of 100% single phase Al2Cu and of 95% Q-phase, respectively, were obtained. The composition of the Q-phase was measured by Energy Dispersive X-ray Spectroscopy (EDX). The measured concentrations are close to the Al3Cu2Mg9Si7 composition that has recently been predicted as most stable by ab initio calculations. A peritectic temperature of 703 °C for the reaction Q → L + Mg2Si + (Si) was determined by differential scanning calorimetry (DSC). An optimization of the Calphad database was performed considering the measured composition and peritectic temperature. For validating the optimized database, Scheil calculations were performed and compared with the experimentally determined sequence of solidifying phases.

► Samples consisting of pure Al2Cu and 95% Q-phase respectively were prepared.
► The Q-phase composition is Al17Cu9Mg44Si30, its solubility range is negligible.
► The Q-phase peritectic temperature was determined by DSC measurements as 703 °C.
► A new thermodynamic dataset for the Q-phase has been assessed.