Farhad Bakhtiari Argesi

Bio: Farhad Bakhtiari Argesi is an academic researcher from Amirkabir University of Technology. The author has contributed to research in topics: Welding & Friction stir welding. The author has an hindex of 2, co-authored 2 publications receiving 28 citations.

Dissimilar Joining of Pure Copper to Aluminum Alloy via Friction Stir Welding

Abstract: In this study, the dissimilar friction stir welding (FSW) butt joints between aluminum alloy 5754-H114 and commercially pure copper were investigated. The thickness of welded plates was 4 mm and the aluminum plate was placed on the advancing side. In order to obtain a suitable flow and a better material mixing, a 1-mm offset was considered for the aluminum plate, toward the butt centerline. For investigating the microstructure and mechanical properties of FSWed joints, optical microscopy and mechanical tests (i.e., uniaxial tensile test and microhardness) were used, respectively. Furthermore, the analysis of intermetallic compounds and fracture surface was examined by scanning electron microscopy and X-ray diffraction. The effect of heat generation on the mechanical properties and microstructure of the FSWed joints was investigated. The results showed that there is an optimum amount of heat input. The intermetallic compounds formed in FSWed joints were Al4Cu9 and Al2Cu. The best results were found in joints with 1000 rpm rotational speed and 100 mm/min travel speed. The tensile strength was found as 219 MPa, which reached 84% of the aluminum base strength. Moreover, maximum value of the microhardness of the stir zone (SZ) was attained as about 120 HV, which was greatly depended on the grain size, intermetallic compounds and copper pieces in SZ.

Alloy Phase Diagrams

Abstract: With the presentation of a theory of liquid alloys, we have now assembled all the necessary tools for the ab initio construction of an alloy phase diagram.

Investigation of the microstructure, mechanical and wear properties of AA6061-T6 friction stir weldments with different particulate reinforcements addition

Abstract: Welding of heat-treated AA6061-T6 often results in mechanical and wear properties deterioration because of the dissolution of the strengthening precipitates at the joint. Enhancement of these properties has been accomplished for non-heat treatable aluminium alloys through the addition of reinforcement particles in the joint. However, its application to AA6061-T6 is scarce. In this work, the microstructure, hardness and wear resistance of AA6061-T6 friction stir welded joints reinforced with SiC, B 4 C and Al 2 O 3 particles were investigated while the base metal and the unreinforced welded joint were utilised as the control. Aluminium matrix grains refinement which improved with increased particle distribution homogeneity occurred in the entire welded joints. All the reinforced welded joints showed improvements on the unreinforced joint in terms of hardness and wear resistance because of the particles high hardness and substantially increased grain refinement that occurred in the reinforced welded joints. Due to B 4 C extremely high hardness and homogeneous distribution in the joint, B 4 C reinforced joint exhibited the highest improvements in hardness (˜42%) and wear rate (˜67%) at low-load condition. However, at high-load condition, SiC followed by the Al 2 O 3 reinforced joints showed the least wear rate even lower than the base metal. The matrix hardness significantly influenced the wear performance at low-load but the overall effects of the reinforcement particles were predominant at high-load condition. The reinforcements’ additions reduced the wear rate of the welded joint by up to a factor of ˜1.7 and ˜1.9 at low and high load conditions respectively.

Achieving a High-Strength CoCrFeNiCu High-Entropy Alloy with an Ultrafine-Grained Structure via Friction Stir Processing

Abstract: High-entropy alloys (HEAs) are a new class of materials with a potential engineering application, but how to obtain ultrafine or nano-sized crystal structures of HEAs has been a challenge. Here, we first presented an equiatomic CoCrFeNiCu HEA with excellent mechanical properties obtained via friction stir processing (FSP). After FSP, the Cu element segregation in the cast CoCrFeNiCu HEA was almost eliminated, and the cast coarse two-phase structure (several micrometers) was changed into an ultrafine-grained single-phase structure (150 nm) with a large fraction of high-angle grain boundaries and nanoscale deformation twins. This unique microstructure was mainly attributed to the severe plastic deformation during FSP, and the sluggish diffusion effect in dynamics and the lattice distortion effect in crystallography for HEAs. Furthermore, FSP largely improved the hardness and yield strength of the CoCrFeNiCu HEA with a value of 380 HV and more than 1150 MPa, respectively, which were > 1.5 times higher than those of the base material. The great strengthening after FSP was mainly attributed to the significant grain refinement with large lattice distortion and nano-twins. This study provides a new method to largely refine the microstructure and improve the strength of cast CoCrFeNiCu HEAs.