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Showing 4 results for Movahedi
The effect of rotation speed to traverse speed ratio and number of welding passes on thermo-mechanical stability of severely plastic deformed aluminum joined by friction stir welding and graphite/Al2O3 hybrid powder
S.e. Moosavi, M. Movahedi, M. Kazeminezhad,
Volume 8, Issue 1 (Journal OF Welding Science and Technology 2022)
Abstract
In this study, thermo-mechanical stability of two-pass constrained groove pressing (CGP) AA1050 sheets towards friction stir welding (FSW) employing hybrid powder (%50vol. micrometric graphite powder+%50vol. α-Al2O3 nanoparticles) was investigated by examining its microstructural evolutions and mechanical properties. FSW was carried out via different process variables in order to reach the highest ultimate mechanical properties of joints. The welding variables employed in this study were single-pass and multi-pass FSW, and different rotation speed to traverse speed ratios (ω/v) were. In order to appraise the powder effect on mechanical properties in the fabricated hybrid metal matrix composite (HMMC), some CGPed sheets were also welded with no powder. Besides optical microscopy and field emission scanning electron microscopy (FESEM) observations, Vickers microhardness and transverse tensile tests were conducted to examine mechanical properties of the weld zone. It was revealed that the effect of graphite powder as a solid lubricant was substantially influenced by the welding variables. More precisely, by employing graphite powder during the FSW, the peak temperature decreased to 224 ℃, while the peak temperature of 489 ℃ was resulted by welding without any powder. Thus, the thermo-mechanical stability of CGPed aluminum and their mechanical properties were enhanced. On the other hand, graphite powder can be responsible for mechanical properties drop due to deteriorating material flow. In addition, different strengthening mechanisms, including grain boundary Zener-pinning and particulate stimulated nucleation (PSN) mechanism, were provided and governed by both powders. However, increasing the ω/v ratio was a practical approach to obtain uniform powder distribution, and consequently, to attain ultimate mechanical properties. Moreover, weld soundness was perceived to be achievable by increasing the number of FSW passes due to eliminating the cavities and improved material flow, resulting in an ultimate tensile strength of 101 MPa, as an optimum efficiency of ~ %80, in three-pass FSW at ω/v=70.
 

Investigation of microstructure and physical properties in nanocomposite solder reinforced with various percent of graphene nanosheets (SAC0307+GNSs)
S. Azghandirad, M. Movahedi, A. Kokabi, M. Tamizi,
Volume 8, Issue 1 (Journal OF Welding Science and Technology 2022)
Abstract
Development of electronic industries, compression of electronic equipment, and removing lead from electronic circuits for environmental issues, resulted in a significant challenge in design and development of tin-based lead-free solders with physical and mechanical properties similar to old tin-lead alloys. In this regard, the set of Sn-Ag-Cu alloys with eutectic and near eutectic compositions have been proposed to replace Sn-Pb solders. As a lead-free solder alloy, low melting point, high reliability, and compatibility with various fluxes are among the properties of this category of alloys. In order to improve the properties of the joint, these solders are sometimes reinforced with different nanoparticles. In this study, Sn0.3Ag0.7Cu compound reinforced with graphene nanosheets with different weight percentages (0, 0.05, 0.1, and 0.2) was studied. Microstructure of the alloys was investigated by scanning electron microscopy(SEM) and optical microscopy. Melting temperature, wetting behavior and electrical resistivity of the solders were evaluated. According to the results, by adding graphene nanosheets, the wetting angle of the solder first decreased and then increased. This parameter showed the optimal amount for sample containing %0.1 graphene nanosheets with a %10 reduction. The melting point and electrical resistance of the solder alloy did not change significantly with compositing. With the addition of graphene nanosheets, the thickness of the intermetallic compounds Cu6Sn5 present at the interface between copper and solder was reduced up to %30.
 

Investigation of microstructure and mechanical properties of lead free composite solder containing cobalt microparticles produced by accumulative roll bonding
M.h. Nourmohammadi, M. Movahedi, A.h. Kokabi, M. Tamizi,
Volume 9, Issue 1 (Journal OF Welding Science and Technology 2023)
Abstract
The miniaturization and compaction trends in electronic equipment and the removal of lead (Pb) element from solder alloys due to environmental considerations have created a great challenge in the field of designing and developing of new solder alloys. Therefore, researchers have recently focused on composite solder alloys using reinforcing particles to improve the reliability of lead-free solders. In this research, SAC0307 solder alloys (99 wt.% Sn, 0.3 wt.% Ag, and 0.7 wt.% Cu) with different percentages of cobalt microparticles were made by the Accumulative Roll Bonding (ARB) method. Then, the effect of the particles on wettability, microstructures and mechanical characteristics of solder alloys was investigated. The lowest contact angle was 23◦in 0.2 wt.% cobalt sample. By adding cobalt to the solder matrix, the size of intermetallic compounds (IMCs), Cu6Sn5 and Ag3Sn, decreased and the percentage of eutectic phases increased. The shape of the interfacial intermetallic compounds changed from scallop to layer shape by adding cobalt, and their average thickness increased about 13-71% in composite samples. The shear strength of solders increased up to 38% by enhancement of cobalt microparticles in the solder alloy containing 0.4 wt.% cobalt; however, shear strength was decreased in the composite solder containing 1 wt.% cobalt due to the agglomeration of microparticles. The shear fracture surfaces showed that the nature of the fracture changed from ductile fracture in the form of elongated dimples to brittle fracture in the form of cleavage with the increase in the percentage of cobalt microparticles. The composite solder alloys containing 0.2-0.4 wt.% Co have the best wettability behavior and tensile shear strength.

Investigating the electromigration resistance of composite lead-free solder alloy containing cobalt particles
Mojtaba Movahedi, Dr Amir Hossein Kokabi, Engineer Mohammad Hadi Nourmohammadi,
Volume 9, Issue 2 (Journal OF Welding Science and Technology 2024)
Abstract
In today's technological landscape, the push for miniaturization in electronic devices is greater than ever, driven by technological advancements. The challenges of electron and thermal migration have arisen due to the need to establish new electronic connections under conditions characterized by creeping temperatures, originating from the low melting point of solders and high current density.  Therefore, recently, alloying and composite materials have been employed to enhance the resistance of electronic connections to electromigration. In this study, efforts to enhance the resistance to electromigration using a composite SAC0307 lead-free solder alloy incorporating cobalt microparticles. The presence of cobalt in the intermetallic composition of the interface causes more stability of the intermetallic composition of the interface and prevents the reduction of the thickness of the intermetallic composition of the interface during the time of the electromigration test; As a result, the stability and electronic connection of the sample soldered with composite solder alloy is more than that of non-composite solder alloy. On the other hand, due to the fine grain structure and the increase in grain boundary density in the composite solder alloy, the lattice diffusion mechanism in the non-composite solder alloy has been changed to the grain boundary diffusion mechanism; As a result, due to the consumption of copper atoms flowed from the cathode side to the anode by the intermetallic compounds present in the grain boundaries, non-uniform microstructural was observed in the composite solder alloy during the time of electromigration test.
 
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