| Direct chill (DC) cast ingot plates of the AA2618 (Al-Cu-Mg-Fe-Ni) alloy have recently been proposed for the manufacture of large molds in the plastic and automotive industries due to the excellent mechanical properties and dimensional stability. The cast plates are cut directly from the DC cast ingot and used in the non-deformed condition, i.e. without hot and cold rolling usually applied to wrought Al alloys. AA2618 alloy is originally designated as a wrought alloy and has therefore not been widely studied in the non-deformed condition. The present work is undertaken to study the effects of heat treatment on the microstructure and mechanical properties of non-deformed AA2618 DC cast alloy, proposed for the manufacturing of molding plates, in order to find the optimum heat-treatment procedures that can be applied to this alloy.;The microstructure of the AA2618 DC cast alloy was firstly examined in the as-cast and solution-treated conditions using optical and scanning electron microscopes, as well as energy dispersive X-ray spectrometer. Jominy end quench test was conducted to evaluate the quench sensitivity of the alloy. Hardness and tensile tests were carried out for different solution treatment, quenching, and aging conditions. The precipitation characteristics of the alloy were studied by differential scanning calorimetry (DSC) technique and electrical conductivity measurement.;An assessment of the microstructure reveals that Al2Cu, Al 2CuMg, Al7Cu4Ni, Al7Cu2(Fe,Ni), and Al9FeNi phases are the main microstructural constituents of the as-cast AA2618 alloy. Solution treatment carried out at 530 °C for 5 h was found to be the optimum solution treatment, which is able to dissolve the Al2CuMg, Al2Cu and Al7Cu4Ni phases completely into the solid solution, thereby enhancing the subsequent precipitation strengthening effect. The Al7Cu2(Fe,Ni) and Al9FeNi phases were only subjected to fragmentation and spheroidization after the solution treatment. The effect of solution soaking time on the microstructure and mechanical properties of the AA2618 alloy is not as significant as that of the solution temperature.;The evaluation of mechanical properties of the solutionized AA2618 alloy after quenching at different cooling rates shows that this alloy is a quench sensitive aluminum alloy. For the same solution and aging conditions, the air cooled samples yields lower hardness and strength values than water quenched samples. The Jominy end quench test results demonstrated that the hardness value of the AA2618 alloy declines significantly with decreasing the cooling rate.;Aging characteristics reveal that the peak-aged conditions of the AA2618 alloy were attained after aging for 36 h at 175 °C, 10 h at 195 °C and 1 h at 215 °C. The aging treatments applied to the AA2618 alloy could produce a wide range of satisfactory combinations of strength and ductility, which may satisfactorily fulfill the specification of the large mold manufacturers. AA2618 alloy was also found to be prone to the natural aging, displaying hardness values comparable to those obtained by the artificial aging at 195 and 215 °C. Results from the DSC analysis and electrical conductivity measurements show that, the main strengthening phase of the AA2618 alloy, under artificial aging, is S-Al2CuMg phase, whereas the strengthening effect caused by the natural aging is probably attributed to the formation of Cu-Mg co-clusters and/or GPB zones. |
