Firouz Fadaeifard

Influence of rotational speed on mechanical properties of friction stir lap welded 6061-T6 Al alloy

The effect of rotational speed on macro and microstructures, hardness, lap shear performance and failure mode of friction stir lap welding on AA6061-T6 Al alloy with 5 mm in thickness was studied by field-emission scanning electron microscopy (FE-SEM). The results represent much closer hardness distribution in the upper and lower plates at the lowest rotational speed. It indicates the Fe-compounds in the fracture surface of the nugget zone by EDX.

Corrosion evaluation of friction stir welded lap joints of AA6061-T6 aluminum alloy

Abstract Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polarization, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize corrosion morphology and to realize corrosion mechanism of weld regions as opposed to the parent alloy. The microstructure and shear strength of welded joint were fully investigated. The results indicate that, compared with the parent alloy, the weld regions are susceptible to intergranular and pitting attacks in the test solution during immersion time. The obtained results of lap shear testing disclose that tensile shear strength of the welds is 128 MPa which is more than 60% of the strength of parent alloy in lap shear testing. Electrochemical results show that the protection potentials of the WNZ and HAZ regions are more negative than the pitting potential. This means that the WNZ and HAZ regions do not show more tendencies to pitting corrosion. Corrosion resistance of parent alloy is higher than that for the weldments, and the lowest corrosion resistance is related to the heat affected zone. The pitting attacks originate from the edge of intermetallic particles as the cathode compared with the Al matrix due to their high self-corrosion potential. It is supposed that by increasing intermetallic particle distributed throughout the matrix of weld regions, the galvanic corrosion couples are increased, and hence decrease the corrosion resistance of weld regions.

Multi-Objective Optimization of Friction Stir Welding Process Parameters of AA6061-T6 and AA7075-T6 Using a Biogeography Based Optimization Algorithm

The development of Friction Stir Welding (FSW) has provided an alternative approach for producing high-quality welds, in a fast and reliable manner. This study focuses on the mechanical properties of the dissimilar friction stir welding of AA6061-T6 and AA7075-T6 aluminum alloys. The FSW process parameters such as tool rotational speed, tool traverse speed, tilt angle, and tool offset influence the mechanical properties of the friction stir welded joints significantly. A mathematical regression model is developed to determine the empirical relationship between the FSW process parameters and mechanical properties, and the results are validated. In order to obtain the optimal values of process parameters that simultaneously optimize the ultimate tensile strength, elongation, and minimum hardness in the heat affected zone (HAZ), a metaheuristic, multi objective algorithm based on biogeography based optimization is proposed. The Pareto optimal frontiers for triple and dual objective functions are obtained and the best optimal solution is selected through using two different decision making techniques, technique for order of preference by similarity to ideal solution (TOPSIS) and Shannon’s entropy.

Effect of post weld heat treatment on microstructure and mechanical properties of gas tungsten arc welded AA6061-T6 alloy

Abstract Double-V butt TIG welding process was performed on two plates of AA6061-T6 using ER5356 filler. The microstructure, mechanical and nanomechanical properties of the joint were evaluated in as-welded and after post weld heat treatment (PWHT) using XRD, FESEM, EBSD, nanoindentation and tensile tests. The results show that PWHT led to microstructural recovery of the heat affected zone (HAZ) in addition to the appearance of β -phase (Al 3 Mg 2 ) at the grain boundaries of weld zone. The hardness ( H nano ) in all zones increased after PWHT while the elastic modulus ( E nano ) was improved from 69.93 GPa to 81 GPa in weld area. All results indicate that PWHT has created a homogenous microstructure in the weld zone in addition to outstanding improvement in mechanical properties for the weld zone which surpass the base metal.

Nano-mechanical properties and microstructure of UFG brass tubes processed by parallel tubular channel angular pressing

The production of the ultrafine-grained brass tubes was carried out by multi-pass parallel tubular channel angular pressing (PTCAP) as a severe plastic deformation process. In addition to that, the microstructural and nano-mechanical features were investigated by EBSD and Nanoindentation for 0, 1, and 3 passes in a comparable mode. The elastic-plastic and micro scratch behavior were analyzed to show the enhanced features. Based on the obtained results, Young’s modulus and hardness of the specimens shifted to 1.62 and 1.7 times of the coarse-grained counterpart after the third pass respectively. The effects of the number of passes on the grain refinement were also investigated to detect the applied changes through each step of the PTCAP experimental procedures. Moreover, based on the obtained results from EBSD, the grain size of 1 and 3 pass samples were refined to 780 and 590 nm from its initial size of 75 µm. The fraction of the high-angle grain boundaries was increased from 30% in pass 1 to 66% in pass 3 of the PTCAP process.

Effect of Artificial Aging on the Microstructure and Mechanical Properties of Aluminum Alloy AA6061-T6

The properties of aluminum alloy AA6061-T6 after aging at 220°C for 0.5 – 8 h are studied by the methods of light and scanning electron microscopy and fractography. The mechanical characteristics of the alloy are determined by tensile tests.