Journal of Advanced Materials in Engineering (Esteghlal)

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An important parameter in composite materials is mechanical behavior and matrix-reinforcement interface interaction under applied stresses. In this investigation, bending strength of carbon-carbon composites synthesized from wood was analyzed as a measure of the composite mechanical properties. Also, densification efficiency of the products was determined by measuring the bulk density and open porosity percentage. Using scanning electron microscopy, optical microscopy, X-Ray diffraction, and Raman spectroscopy, the final product was examined to evaluate and interpret the morphology and internal texture and results of mechanical test. The results showed that we are able to use an ordinary material such as wood for production of a unique product with great properties called two-dimensional carbon-carbon composites.

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In the present article, RRA, T73 and T6 heat treatments were carried out to improve mechanical properties of 7075 aluminum alloy and its hardness, tensile and bending strengths were evaluated. For this purpose, solution annealing was performed at 530 ºC for 16 h. For T6 treatment, aging was executed at 150 ºC for 24 h after solution annealing. In T73, aging treatment was done in two stages after solution annealin, at 120 and 180 ºC for 7 and 20 h, respectively. RRA treatment was performed in three stages. The first stage was the same as T6 treatment, the second stage constitutes tempering at 200 ºC for
20 min and in the third stage aging process was repeated like T6 treatment. Evaluation of the microstructures and fractured surfaces were performed with optical microscopes (OM) and scanning electron microscopes (SEM). Energy dispersive spectroscopy (EDS) was used to study the chemical composition of precipitates. Hardness, tensile and bending strength were evaluated according to ASTM E384-11e1, ASTM B557-06 and DIN 50121 standards. RRA treatment increased tensile strength from 466 to 485 MPa and hardness from 110 to 165 Vickers. After T6 treatment, tensile strength increased from 466 to 505 MPa and hardness from 110 to 160 Vickers. In T73 process, the tensile strength remained almost constant (465 MPa) but yield strength increased from 394 to 410 MPa and hardness decreased from 110 to 84 Vickers. The bending strength increased from 797 to 844, 920 and 1030 MPa in T73, RRA and T6 processes, respectively. By applying RRA process in optimized temperature and time, hardness, tensile and bending strengths of 7075 aluminum alloy were enhanced from 5 to 15% compared to that of T6 and T73 processes.