مجله علوم و فناوری جوشکاری ایران
سال هشتم شماره 1 (پیاپی 14، بهار و تابستان 1401)

In this study, to bond AA2024 and AA6061 alloys to each other, three elements (Sn, Zn and Ga)  were considered as interlayer elements in terms of atomic diffusion depth in the base metal and storage at 453°C for 2 days, 10 hours, 210 minutes, and 30 seconds that they were examined for atomic diffusion modeling. Finally, the two alloys were connected at a temperature of 453°C in a furnace environment under a vacuum of 7.5×10-13 Torr under a transient liquid phase process. The effect of changing the thickness of the interlayer on the connection of the two alloys are examined with practical tests such as metallography, SEM, the distribution map of the elements, hardness test, the linear scan of the elements at the joint, and tensile strength test in two modes, 1: investigating the effect of changing the thickness of the interlayer on strength, and 2: investigating the change in joint strength by increasing sample retention time in the furnace. As the thickness of the interlayer increases (from 20 to 70 μm), the bond strength decreases. The maximum tensile strength of joint with the 20 μm thickness Sn-5.3Ag-4.6Bi interlayer is 52 MPa.

The welding joints were investigated due to the significance of similar welding of Corten A weathering steel and its dissimilar welding with St12 plain carbon steel in industrial applications. The gas metal arc welding (GMAW) technique with carbon dioxide shielding gas was utilized in the present work. The welding process comprised current and voltage control, welding wire injection rate, shielding gas rate, welding speed, connection configuration, and microstructure evolution. Mechanical properties and microstructure evolution in similar and dissimilar joints and weld defects were evaluated by tensile, bending, hardness, metallographic, and radiographic tests. The weld microstructure in similar and dissimilar joints included grain boundary ferrite, acicular ferrite, and WidmanStatten ferrite. The tensile strengths of the similar and dissimilar joints were respectively 497 and 303 MPa. The weld zone hardness was 210 and 180 Vickers for similar and dissimilar joints, respectively. In conclusion, similar welding outperformed dissimilar welding considering weld joint defects, mechanical properties, and microstructure.

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.

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.

In this research, the diffusion bonding of the stabilized zirconia ceramic and Nimonic 105 superalloy using Ti/Nb/Ni multi-interlayer was carried out. Joint was performed using the plasma spark technique in a vacuum atmosphere and at different temperatures and times. The microstructure of the different joint zones was studied using optical and FESEM microscopes equipped with an EDS analyzer. The results showed that the critical region is Ti/3YSZ interface and in all conditions diffusion bonding in Ti/Nb, Nb/Ni, and Ni/NI 105 interfaces were done. Microstructural observations showed that in the Ti/3YSZ interface at all temperature and time conditions, the connection of two separate regions including Ti3O and (Zr, Ti)2O was formed due to the difference in the diffusion depth of Ti, Zr, and O elements and with increasing temperature and time, the thickness of these regions increased. Microstructural studies showed that the bond at 900 ℃  and 30 minutes did not have any cracks and discontinuities and due to the better diffusion of atoms, a suitable reaction layer was formed. Microhardness observations and EDS analyses confirmed that the Ti3O reaction layer is the weakest zine.

The aim of the present study is to investigate the mechanical and microstructural properties of 1.7225 steel in laser welding process using Nd:YAG pulsed laser device and then to determine the optimal focal length relative to the part in the welding area. After welding, microstructural characterization, microhardness and tensile tests were performed. Evaluations showed that the optimal focal length for welding of steel sheet 1.7225 with a thickness of 1 mm, it was about 9 mm and the focus was 1 mm below the surface of the part. Due to the high thermal concentration and cooling rate in laser welding, a completely martensitic microstructure has been observed in the molten and heat-affected regions of all specimens. In this alloy, the hardness of the base metal is 310±10 HV. After welding, the hardness of the sample with the optimal focal length   has reached 625±10 HV in the heat affected zone and 730±10 HV in the melting zone. Also, the results of tensile test showed that the tensile properties of the sample with the optimal focal length were almost similar to the base steel and fracture was observed in the base steel region.

In this investigation the effect of oxides powders of SiO2, MoO3 and CuO on the depth of penetration, microstructure and hardness profile of GTAWeld precipitation hardening martensitic 17-4PH was assessed. Samples were taken from 17-4PH steel sheet with the dimensions of 150*50 mm and with the thickness of 5 mm, and were welded by oxide powder of SiO2, MoO3 and CuO. Results showed that using oxide powder increased the penetration depth of the welded joints by about 150 percent compared to the normal condition. Also, it was shown that although using SiO2 powder increased the penetration depth to about 7.49 mm, it provides inferior weld bead appearance. The use of MoO3 and CuO powder increased the penetration depth of the weld to about 5.3 mm. Although inclusions were found throughout the side of the weld bead when MoO3 powder was employed for welding. The microstructure of the weld in different samples did not vary and included dendritic structure with delta ferrite located between the dendrites. The hardness profile of the welded joints showed the closeness of the hardness of the welded joints using different oxide powder with the base metal.

Surface roughness in the welding processes is one of the important parameters in the laser welded metal connections which affects laser beam absorption directly. When the laser beam is irradiated to the surface of the base metal, the surface roughness plays an important role in the amount of beam absorption and the amount of melting achieved and directly affects the penetration depth. The main purpose of this study is to investigate the effect of roughness mentioned above in the equal parameter for this widely used aluminum alloy. Microstructural Surveys were performed on three different roughness levels of the sample and the results obtained from the analysis of samples by optical microscope (OM), atomic force microscope (AFM) and Scanning electron microscopy (SEM) analysis showed that, increasing the surface roughness up to Ra = 0.16 micrometer, caused the greater degree of beam engagement by the surface grooves, hence more concentration of the beam photons and more melting obtained, so the depth of penetration increases by consuming a lower amount of energy.

In the present study, the microstructure and mechanical properties of the dissimilar joint of Inconel 625 (IN-625) superalloy to austenitic stainless steel AISI316L (SS-316L) via AWS-BNi3 interface layer and transient liquid phase (TLP) bonding process were evaluated and necessary conditions for creating an efficient joint were determined. TLP bonding was performed in temperature and time range of 1050-1150ºC and 5-20min, respectively, under the protection of argon shielding gas with a purity of 99.9995%. Microstructural (OM and SEM) and phase (XRD) studies revealed that bonding at 1150 ° C for 20 min results in completion of isothermal solidification and develops a uniform gamma (γ) phase at the bonding zone. Cooling the samples before completion of isothermal solidification results in the formation of chromium and molybdenum-rich eutectic compounds at the bonding centerline. The continuous morphology of the eutectic compounds caused a sharp drop in the shear strength of the specimens (~50% reduction of shear strength). The inter-diffusion of alloying elements between the bonding area and the surrounding base metal results in the formation of chromium carbide in the IN-625 and chromium- boron compounds in the SS-316L, which increased the microhardness of these areas compared to the base metals and the bonding zone.

Todays, application of composite materials has been increased in various industries due to their special strength properties and also other unique features. One of the important things during making of such materials, is their connection to each other. In this article, the Joining of heat-hardened parts with surface preparation with the help of laser, simple and rough, has been investigated. The main goal is to investigate the better surface adhesion mechanisms of the connection compared to the simple surface, as well as to create practical approaches to increase the adhesion strength of the thermosetting parts. The composites were made of heat-hardened epoxy resin (which hardens after 12 hours at room temperature) and two-dimensional woven glass fibers and were connected by glue after volume heating at a temperature of 180-200 degree Celsius. In this research, the overlapping surface of the part was engraved by laser in circular patterns. The raw parts were prepared by manual polishing and mechanical abrasion. The results show that by examining the effect of surface roughness and composite thickness, the highest value of shear strength is related to the surface roughness compared to other preparation methods. Surface preparation increases the amount of adhesive penetration in the parts and expands the tensile strength. The thickness also has a conditional effect on the strength of the connection.

The influence of filler metals on the microstructure and corrosion behavior of AISI 316L welds was investigated. Gas Tungsten Arc welding (GTAW) process was applied to join the AISI 316L plates using ER 316L and ER 312 filler metals. The obtained microstructures were characterized by optical metallography and scanning electron microscope (SEM). Corrosion assessments were conducted in 3.5% NaCl using a three electrode cell.  Open circuit potential and potentiodynamic polarization examinations were conducted on the welds and base metal. Microstructural evaluations indicated that a combination of austenite and ferrite phases was formed in the welds fabricated by both filler metals. Based on the micro hardness tests, the weld fabricated by ER 312 filler exhibited superior harness compared to the ER 316L weld. Corrosion evaluations also show that the weld metal obtained from two filler metals has a lower corrosion rate due to the higher amount of chromium and higher ferrite compared to the base metal. Also, the lower corrosion current of ER 312 weld metal compared to ER 316L weld metal is for this reason. In contrast to the base metal compared to the two welding metals, the result of the two filler metals has shown better pitting corrosion results according to the electrochemical tests and also the examination of the surfaces using an optical microscope after these tests, that these results are due to The presence of two phases of austenite and ferrite in the vicinity of each other in weld metals and the intensification of galvanic corrosion is due to the discharge of the austenite phase from chromium and molybdenum.

In this study, DIN 34CrAlNi7 Nitriding steel in two states before and after nitriding, were welded by tungsten-gas arc welding process using two types of fillers (ER309L and ER312). The aim of this research was to investigate the best conditions for welding (before or after nitriding) and also to choose the best filler metal. The microstructure of the joint was examined using an optical microscope. A tensile strength test was also used to evaluate the mechanical properties. Fracture surfaces were also studied using a scanning electron microscope (SEM). According to the results Welding of these steels with ER309L filler is allowed only in the pre-nitriding state. If the base metal is nitriding, due to microstructural changes in the weld metal, filler metal ER309L cannot be used. However, the results of samples welded with ER312 filler metal show that if the base metal mixing percentage is less than 30%, this filler can be used for welding base metals in both before and after nitriding.