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The strongest among the all-aluminum alloy series is 7xxx due to its unique composition of alloying elements, making it perfect for automotive and aerospace applications. The present research included manufacturing of Si₃N₄ reinforced aluminum alloy (AA) 7068 nanocomposites via stir casting combined with ultrasonication, followed by a bottom pouring technique. The Si₃N₄ reinforcement has been conducted in different fractions (0.5, 1, 1.5, and 2%) by weight. The microstructure characterization of prepared composites was conducted using FESEM, EDS, and elemental mapping. The microstructure of the AA7068 matrix was significantly refined after incorporating Si₃N₄ nanoparticles. The hardness of alloy increased with reinforcement addition and maximized at 1.5 wt.% due to the combined effect of hard Si₃N₄, difference in thermal co-efficient, Hall-Petch, and Orowan strengthening mechanism. The wear resistance significantly increased after incorporating (Si₃N₄)np in the alloy by increased load-bearing capacity and hardness of nanocomposites. The wear of alloy and nanocomposites is mainly due to the adhesion, two-body, and three-body abrasion mechanism. Optimization of wear parameters was completed using the Taguchi approach. The L-25 orthogonal array was selected to perform the wear test, and, later, the ANOVA tool was used to understand the percentage contribution of each factor. The load has the maximum contribution of 65.67%, followed by reinforcement wt.% and sliding distance. Minimum wear loss was noticed when the wear test was conducted on optimum wear parameters (1.5 wt.% reinforcement, 10 N load, and 400 m sliding distance). Hardness and wear behavior were oppositely influenced by the clustering of particles found at 2 wt.% nanocomposites. Full article

The mechanical properties after age hardening heat treatment and the kinetics of related phase transformations of high strength AlZnMgCu alloy AA 7068 were investigated. The experimental work includes differential scanning calorimetry (DSC), differential fast scanning calorimetry (DFSC), sophisticated differential dilatometry (DIL), scanning electron microscopy (SEM), as well as hardness and tensile tests. For the kinetic analysis of quench induced precipitation by dilatometry new metrological methods and evaluation procedures were established. Using DSC, dissolution behaviour during heating to solution annealing temperature was investigated. These experiments allowed for identification of the appropriate temperature and duration for the solution heat treatment. Continuous cooling experiments in DSC, DFSC, and DIL determined the kinetics of quench induced precipitation. DSC and DIL revealed several overlapping precipitation reactions. The critical cooling rate for a complete supersaturation of the solid solution has been identified to be 600 to 800 K/s. At slightly subcritical cooling rates quench induced precipitation results in a direct hardening effect resulting in a technological critical cooling rate of about 100 K/s, i.e., the hardness after ageing reaches a saturation level for cooling rates faster than 100 K/s. Maximum yield strength of above 600 MPa and tensile strength of up to 650 MPa were attained. Full article