جستجوی مقالات مرتبط با کلیدواژه « آلومینیم 7075 » در نشریات گروه « مواد و متالورژی »

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.

Thermophysical properties, electrical contact resistance (ECR) and corrosion performance are considered as critical properties of coatings, which are utilized in the satellite manufacturing industry. Chromate conversion coatings (CCCs) for Al alloys are among these coatings.In this study, CCCs were applied on Alclad AA7075-T6 Al Alloy by means of a chromating solution having chemical composition very near to the commercial chromating solution of Alodine 1200S. Influence of coating time on the coatings thermophysical properties including coefficients of solar absorption or Absorptivity (αs) and thermal emission or Emissivity (εT) as well as their ECR values were investigated. The εT was measured directly by Emmisometer device, while αs was determined indirectly by Reflectometer equipment. In coating time from 30 up to 180 seconds αs and εT values were measured in the ranges of 0.7-0.94 and 0.06-0.22, respectively. The results were revealed that different εT and αs as well as desired ECR values according to the specifications of satellite industry are obtainable by control of coating parameters such as coating time. In addition, base on the results of surface coating morphology evaluating conducted by SEM and AFM, it was concluded that developed coatings were formed in nanocrystalized structures.