Sharif Digital Repository

The hot deformation characteristics of 7075 aluminum alloy (AA7075) are investigated by means of hot compression tests carried out in the temperature range of 200-450 C and strain rate range of 0.0003-1 s-1. Two novel processing maps based on flow localization parameter and enhanced DMM are developed and compared with conventional DMM results. It is observed that processing maps based on flow localization parameter can be used successfully to predict AA7075 thermomechanical behavior. Also, the comparison of the DMM results indicates that the new approach to calculate DMM power dissipation efficiency and instability criteria corresponds better with experimental observations. The occurrence of... 

An important aspect of production of gears by precision forging process is the prediction of load required to perform the process and to design the forging die. In this research a new kinematically admissible velocity field is presented to predict the forging load by an upper bound analysis. The analysis considers the shape of tooth profile, number of teeth, and frictional conditions between the die/punch and deforming material. To verify the predicted results the 7075 aluminum alloy billets were forged at temperature of 150 to 250 °C in a precision forging die designed to produce a spur gear of 5 teeth. A good agreement was found between the two sets of results at the filling stage of the... 

In this study, artificial neural network (ANN) was used to model the hot deformation behavior of 7075 aluminum alloy during compression test, in the strain rate range of 0.0003-1 s-1 and temperature range of 200-450 C. The inputs of the model were temperature, strain rate, and strain, while the output of the model was the flow stress. The feed-forward back-propagation network with two hidden layers was built and successfully trained at different deformation domains by Levenberg-Marquardt training algorithm. Comparative analysis of the results obtained from the hyperbolic sine, the power law constitutive equations, and the ANN shows that the newly developed ANN model has a better performance... 

In this study, microstructural changes and mechanical properties during friction stir welding of AA7075-T6 have been investigated. Friction stir welding at relatively high rotational speeds ranging from 1000 to 1400 rpm and longitudinal speeds in the range of 40 to 80 mm/min have been performed and then microstructures and mechanical properties of the weldments have been studied. The results show that the rotational and longitudinal speeds have a significant effect on the microstructures as well as the mechanical behavior of the welded material while a fine grain structure is produced at higher ratio of rotational speed to longitudinal speed. On the other hand, for a given longitudinal... 

In this work, deformation behavior as well as creep and cavitation of AA7075-T76 were studied. The as-received plate was first stabilized utilizing solution treatment followed by two-stage artificial aging at 120 and 180 °C. Then, tensile tests were carried out on the aged-alloy in the temperature range between 120 and 250 °C under strain rates of 0.0005 and 0.005 s−1. Furthermore, stress-controlled creep tests were performed at temperatures varying between 120 and 210 °C at stresses ranging from 130 to 250 MPa. Microstructural evolution was then conducted to assess the microstructural changes and growth of cavities during creep employing optical metallography and scanning electron...