Iranian Journal of Materials Forming
Volume:9 Issue: 3, Summer 2022

The “Iranian Journal of Materials Forming (IJMF)” is an international open-access journal in the fields of materials deformation and forming processes, which was established at Shiraz University in 2014. The journal is pleased to receive papers from scientists and engineers from academic and industrial areas related to all manufacturing processes. In addition, all deformations, including the elastic and plastic behaviors of materials and deformations due to failure, are part of this journal’s field of interest. The quality and credibility of the journal have been ensured by appointing some of the most well-known professors in the world as members of its editorial board. In addition, the wide range of the selected referees in this issue is a sign of its scientific quality. It is a matter of pride that for the second year, this journal has been successfully released quarterly and the third issue was published in 2022.

Commercial pure titanium sheets were thermo-mechanically treated to investigate the effects of the treatment variables on the microstructure, mechanical properties, and recrystallization behavior. The as-received sheets were initially cold-rolled up to different reduction percentages of 60%, 75%, and 90%. Then, the cold-rolled samples were annealed at different temperatures of 500°C-700°C, for various time ranges of 5 to 60 minutes. The evolution of the microstructure of the samples was studied using X-ray diffraction analysis and optical microscopy. The hardness of the 90% cold-rolled sample was about 82% higher than that of the as-received sheet. Increasing the time and temperature of the annealing process caused a decrease in the microhardness values of the samples. The recrystallization activation energy and Avrami’s exponent of the 90% cold-rolled sample were calculated as about 179 kJ/mol and 0.75, respectively. The results of the uniaxial tensile tests revealed that the cold-rolling process significantly improved the yield strength (YS) and ultimate tensile strength (UTS) of the specimens. In the case of the 90% cold-rolled sample, these values improved by about 160% and 117% with respect to the as-received metal, respectively. However, the elongation of the cold-rolled samples dropped sharply. Moreover, annealing had a positive effect on the elongation of the cold-rolled samples. The UTS and elongation percentage of the as-received sheet were 415 MPa and 36.4%, respectively. These values were varied to 558 MPa and 29.15% for the 90% cold-rolled sample annealed at 700°C for 1 h. To study the fracture behavior of the different samples, scanning electron microscopy (SEM) was used.

The present work deals with the microstructure globularization, coarsening behavior and the correlated kinetics during strain-induced melt activation process of AZ61 magnesium alloy. In this study, the effect of pre-strain, temperature and holding time have been considered, and the evolutions were numerically discussed based on Lifshitz-Slyozov-Wagner (LSW) and Ostwald ripening mechanisms. The treated microstructures (undeformed, globular, non-globular, and coarsened) were then hot compressed at a semisolid temperature range to assess the thixotropic flow behavior of the material. A unique microstructure encompassing fine α-Mg globules uniformly distributed in the matrix and surrounded by a liquid phase was developed by imposing 45% pre-strain and holding it at 555°C for 8 min. The lowest deformation resistance belonged to the specimens holding globular microstructures, while those with undeformed characteristics possessed the highest flow stress during thixoforming. The semisolid flow response was discussed considering the flow of liquid that incorporates solid particles (FLS); sliding between solid particles (SS), and plastic deformation of solid particles (PDS) mechanisms. The influence of the shape factor (in globular structure) and the grain size (in coarsened structure) on the thixotropic flow behavior of the experimented alloy were also illustrated.

A multi-objective numerical optimization was used to study the forging process of a Ti-6Al-4V alloy in producing an artificial hip joint implant. The forging temperature was chosen in the Alpha-Beta two phase region around 900°C. In order to implement the numerical simulation, the Deform 3D commercial code was used. Response surface methodology (RSM) was considered and experiments based on various widths (w), thickness of flash (t), and billet diameter (d) were designed to find out the influences of these parameters on flash volume, filling rate and strain non-uniformity as the responses. Twenty numerical tests were implemented by finite element analysis (FEA), and the obtained results were used to optimize the forging process using RSM. To this end, the constants of constitutive and governing equations to FEA and the data of a published paper were applied. The optimized results were w = 8 mm, t = 1.73 mm, and d = 30 mm, for flash geometry and billet diameter, respectively. Finally, an FEA was conducted based on the optimized values, and the results were compared and discussed with those in the Noiyberg-Mokel model for verification.

In this study, the evolution of parallel tubular channel angular pressing (PTCAP) as a severe plastic deformation process on the hot deformation behavior of the extruded AZ31 magnesium tube was investigated. After four passes, a more refined and homogeneous microstructure was achieved. To understand constitutive behavior, hot tensile tests were carried out on four passes of specimens at temperatures of 350, 400, and 450ºC with strain rates of 0.0001, 0.001, and 0.01 s-1. The dependence of flow stress on strain rate and temperature was investigated by the Zener-Hollomon equation and the activation energy was found to be around 131.26 kJ/mol. Effect of strain was included in the constitutive equation by applying material constants. Based on the constitutive model, the stress-strain curves of PTCAP processed tubes were extracted and compared with the experimental curves. The results indicate good agreement between experimental and predicted flow curves by considering the softening effect.

Microstructural evolutions and mechanical properties of a cold-rolled 309S austenitic stainless steel were investigated after reversion annealing in the temperature ranges of 700-1000°C for 3-20 min. The specimen was first cold-rolled at room temperature to 90% thickness reduction. The microstructure was analyzed by optical and SEM methods and the mechanical behavior was studied by tensile tests and hardness measurement. The results depicted that negligible strain-induced ά-martensite was formed after cold-rolling. In addition, elongated austenite grains were observed after deformation followed by annealing below 700°C which was a signature of the recovery process. The recrystallization of the deformed austenite was dominant above 800°C, while recrystallization followed by grain growth were seen at 900°C. Moreover, the significant grain growth was observed at 1000°C. The optimum annealing temperature and time for achievement of a uniform recrystallized grain were at 800°C for 3 min which resulted in considerable grain refinement. The grain refinement led to improvement of mechanical properties of investigated austenitic stainless steel. The hardness value of refined austenite grains was 195% greater than that of the as-received steel. Finally, current work can shed some light on the effect of grain refinement on the control of microstructural and mechanical property of austenitic stainless steels.

The high temperature flow behavior of additively manufactured 316L stainless steel was investigated in this study by hot compression tests at the temperatures of 973, 1073, 1173 and 1273 K and strain rates of 0.001-0.1 s-1. Constitutive models consisting of Johnson-Cook and Arrhenius-type were employed. The results indicated that the Arrhenius-type constitutive equation had higher accuracy than the Johnson-Cook model, but these constitutive models could not predict (i) the strength levels at all temperatures and strain rates, and (ii) the flow hardening/softening behavior, accurately. Therefore, an artificial neural network with a feed-forward back propagation learning algorithm has been established to predict the high temperature flow behavior of additively manufactured 316L stainless steel. This model includes three layers namely the input layer, the hidden layer (with 20 neurons), and the output layer. The input data consisted of true strain (ε), strain rate ( ), and deformation temperature (T) while the predicted flow stress (σ) was the output data. In order to evaluate the performance of employed models, standard statistical parameters such as the average absolute relative error (AARE), root mean square error (RMSE) and correlation coefficients (R) were used. The results showed that the artificial neural network model was more accurate than the constitutive equations in predicting the high temperature flow behavior of additively manufactured 316L stainless steel.