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Optimizing the mechanical properties of Al-4.5Cu-xSi alloys through multi-pass friction stir processing and post-process aging

Mostafavi M., Taghiabadi R., Jafarzadegan M.

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 1

art. no. e11, 2022

The effect of post-process aging on the microstructure and mechanical properties of multi-pass friction stir processed (FSPed) Al-4.5Cu alloy containing Si (1, 3, and 5 wt.%) was studied. According to the results, adding Si improved the fluidity and decreased the porosity content of the alloy. The addition of Si up to 3 wt.% also enhanced the mechanical properties. However, further addition of Si up to 5 wt.% impaired the tensile properties. Applying the first pass of FSP improved the tensile strength and fracture strain of the alloy containing 3 wt.% Si by 25 and 125%, respectively. However, the second and fourth pass of FSP substantially improved the fracture strain, but deteriorated the hardness and tensile strength of the alloy containing 3 wt.% Si. Post-FSP aging at 180 °C for 8 h significantly improved the mechanical properties. For instance, compared to the as-cast condition, the hardness, tensile strength, fracture strain, and toughness of post-aged four-pass FSPed Al-4.5Cu-3Si alloy increased by 107, 108, 175, and 310%, respectively. According to the fractography results, the fracture surface morphology of Al-4.5Cu-3Si alloy changed from a quasi-cleavage mode in as-cast condition to a ductile-dimple fracture mode after post-FSP aging.

Hydrogen bonded complexes of coumarin 153

Królicki R., Jarzęba W., Soroushian B., Lampre I., Mostafavi M.

Bulletin of the Polish Academy of Sciences. Chemistry

2002

Vol. 50, No. 4

435-449

Detailed studies of the hydrogen-bonded complexes of coumarin 153 (C153) have been carried out. It has been shown that nonlinear shifts of the steady-state absorption and fluorescence spectra taken in toluene-methanol solvent mixtures are caused by the formation of hydrogen bonded complexes between C153 and methanol, while preferential solvation plays a minor role only. IR measurements confirmed the ability of C153 to form hydrogen-bonded complexes with methanol and phenol. The stoichiometry of the formed complexes and relevant equilibrium constants have been estimated. Femtosecond solvation dynamics measurements of C153 in the toluene-methanol mixture (xMeOH = 0.2) showed that the average solvation time is higher than that in the pure solvents indicating slower relaxation of methanol in the mixture. The slow component of solvation dynamics (ok 20ps) can be attributed to translational diffusion of methanol to the first solvation shell of C153 and to the relatively slow reorientational motion of methanol involved in formation of hydrogen bond with the excited C153.