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In this study, the wear behavior of AA7075 alloy produced by thixocasting was investigated. The wear behavior of the AA7075 alloy is examined for three cases: extruded with T6 heat treatment, as-thixocast, and thixocast with T6 conditions. The dry sliding wear test was conducted with a tribometer according to ASTM G-99 standard. The microstructures were characterized by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). The tensile and hardness tests were performed to evaluate the mechanical properties. The AA7075 alloy was successfully shaped by thixocasting. The as-thixocast sample exhibited typical globular structures with multinary eutectic structures along the grain boundaries. The globular grains transform into a polygonal structure, and the grain size increases from 50 μm to 60 μm in the thixocast + T6 sample. This microstructure exhibited excellent wear resistance under dry sliding conditions in the thixocast + T6 sample. The aging treatment with prolonged solution process improved the mechanical properties two times and the wear rate three times for the thixocast AA7075 alloy. Furthermore, the thixocast + T6 sample exhibited a significant decrease in the coefficient of friction with the lowest wear rate compared to the as-thixocast sample. The dominant wear mechanisms are microdelamination, adhesion, and oxidation in all samples.
In this study, the wear behavior of AA7075 alloy produced by thixocasting was investigated. The wear behavior of the AA7075 alloy is examined for three cases: extruded with T6 heat treatment, as-thixocast, and thixocast with T6 conditions. The dry sliding wear test was conducted with a tribometer according to ASTM G-99 standard. The microstructures were characterized by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). The tensile and hardness tests were performed to evaluate the mechanical properties. The AA7075 alloy was successfully shaped by thixocasting. The as-thixocast sample exhibited typical globular structures with multinary eutectic structures along the grain boundaries. The globular grains transform into a polygonal structure, and the grain size increases from 50 μm to 60 μm in the thixocast + T6 sample. This microstructure exhibited excellent wear resistance under dry sliding conditions in the thixocast + T6 sample. The aging treatment with prolonged solution process improved the mechanical properties two times and the wear rate three times for the thixocast AA7075 alloy. Furthermore, the thixocast + T6 sample exhibited a significant decrease in the coefficient of friction with the lowest wear rate compared to the as-thixocast sample. The dominant wear mechanisms are microdelamination, adhesion, and oxidation in all samples.
The identification of structural components in the AM4.5Kd + 0.2 wt.% La alloy, subjected to quenching at different temperatures (535–605 °C) and artificial aging at 155 °C for 4 h, was conducted through electron microscopy and XRD. An increase in the quenching temperature from 535 to 605 °C promotes the enlargement of structural components, including the α-solid solution, various aluminides, and eutectics. We observed that the base metal is not homogeneous in its chemical composition, consisting of two types of solid solutions: α1 and α2. The Cu and Mn solubility in the α2-solid solution is higher than in the α1-solid solution. As the quenching temperature increases to tq = 605 °C, the copper content in the α1-solid solution decreases. In contrast, the copper content in the α2-solid solution follows a curve with two maxima at 545 °С (4.5 at.%) and 585 °С (8.7 at.%). The Mn content in the α1-solid solution decreases sharply to the 545 °С quenching temperature and remains relatively constant up to tq = 605 °С (0.2 at.%). The Mn content in the α2-solid solution follows a curve with its maximum at tq = 545 °С (4.3 at.% Mn). Subsequent temperature rise results in a sharp drop in Mn content from 1.0 at.% at t = 565 °С to 0.3 at.% at 605 °С. Hence, the max solubility of Cu and Mn in the α2-solid solution occurs at 545 °C. At 585 °С, only an elevated Cu content (~8.7 at.%) was observed. Aluminides of alloying elements with different stoichiometries crystallize at different quenching temperatures, with complex AlxTiyLazCuvCdw and AlxCuyMnzCdv alloyed aluminides being most commonly found. ncreasing the quenching temperature to 535–545 °С results in higher hardness of the AM4.5Kd + 0.2 wt.% of La alloy, reaching 98–104 HB, with subsequent decrease to 60 HB as the quenching temperature reaches 605 °С. The hardness of the unhardened alloy is 60 HB. The optimal quenching temperature for the AM4.5Kd + 0.2 wt.% of La alloy is in the range of 535–545 °С. This temperature corresponds to the highest hardness of the alloy and the microhardness of the aluminide.
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