Sintering response & microstructural evolution of an Al-Cu-Mg-Si premix

The sintering behavior of a powder premix (Al-4.4 w/o Cu-0.5 w/o Mg-0.7 w/o Si) has been studied. Reactions occurring during liquid-phase sintering of this alloy have been identified by means of differential scanning calorimetry (DSC), dilatometry, sintering experiments, and microstructural analysis, including energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). The first reaction observed is the formation of aluminum-magnesium liquid at similar to 450 degrees C. This reaction is followed by other reactions at 505 degrees C and 550 degrees C which are related to the incorporation of copper into the liquid phase at the same time that magnesium, silicon, and copper diffuse into the solid aluminum particles. Swelling of the powder compact during the initial sintering stage is related to chemical homogenization of the alloy, and to spreading of the liquid phase. Following a complex sintering cycle with a slow heating rate after de-waxing (2 degrees C/min), a first holding step for 20 min at 570 degrees C in vacuum, and a second holding step at 590 degrees C for 20 min in nitrogen, a final density similar to 98% of the pore-free level was obtained. Tensile properties and hardness of the alloy were determined in the assintered and heat-treated (T4 and T6) conditions. Optimal results were: ultimate tensile strength 388 +/- 26 MPa and elongation to fracture 0.26%-0.73% in the T6 condition.