Journal of Welding Science

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In the TIG-MIG hybrid welding, higher weld efficiency and better weld quality are obtained with respect to each individual TIG and MIG welding methods. Moreover, in this method, the MIG arc is more stable in pure argon shielding gas. Therefore, in this study, the influence of TIG-MIG hybrid welding parameters on the welds appearance quality and welds depth to width ratio of a 316L austenitic stainless steel was investigated using optimum parameters of Taguchi design of experiments (DOE). Microstructure of the heat affected zone (HAZ) obtained from the hybrid welding was compared with those of each individual MIG and TIG welding techniques under equal heat-input condition. The results indicated that the most important parameter in the hybrid method to obtain the best appearance quality and the highest depth to width ratio is the distance between the two arcs. The MIG and TIG currents are the next influencing parameters. The width of HAZ and the size of constituent grains in hybrid welding with optimum parameter, were smaller than those of each individual TIG and MIG processes due to the higher associated cooling rate in the hybrid welding technique.

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In the present study, effect of inclusions characteristics changing on the formation of acicular ferrite in submerged arc welding of API5l-X65 low alloy steel was investigated. Three different welding fluxes with different chemical composition and basicity index of 0.72, 0.82 and 0.99, and two different welding heat inputs of 1.6 kJ / mm and 2.4 kJ / mm were used to create inclusions with different characteristics such as chemical composition and size. The results indicate that inclusions acting as acicular ferrite nucleation sites and improvement of the microstructure and resulted mechanical properties, can be observed in welding conditions in which the welding flux with lowest basicity index and higher welding heat input. Under these conditions, the percentage of inclusions with a high titanium oxide value and size range of 0.5 to 1.5 micrometers is increased, which increases the amount of acicular ferrite in the microstructure. However, in other welding conditions, formation of grain boundary ferrite reduces amount of acicular ferrite and weakens mechanical properties of weld metal compared to the base metal.

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Friction stir welding (FSW) was conducted on AISI 304 austenitic stainless steel plate with 2 mm thickness. The FSW was performed at a welding and rotational speeds of 50 mm/min and 400 rpm, respectively. Microstructure observations by the optical microscopy showed that a severe grain refinement occurred in the stir zone (SZ). Electron backscattered diffraction analysis (EBSD) results indicated that high fraction of low angle grain boundaries (LAGBs) developed in the thermo-mechanically affected zone (TMAZ) through the occurrence of the dynamic recovery. Moreover, in the path from the TMAZ towards the SZ, the fraction of high angle grain boundaries (HAGBs) increased with decreasing the fraction of LAGBs through the occurrence of continuous dynamic recrystallization (CDRX). 100 Pole figure showed the formation of shear texture components of A*1 and A*2 in the SZ which implied the occurrence of CDRX mechanism.
 

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In this research, dissimilar welding of NiTi shape memory alloy to AISI 304 austenitic stainless steel Archwires was investigated. For this purpose, common straight orthodontic archwire with rectangular cross-section and dimensions of (0.635 × 0.432 mm) were selected and the laser welding technique was used to connect the wires. The microstructure, chemical composition and phasesin the weld zone of the joints werestudied with Optical microscopy (OM), Scanning electron microscopy (SEM) equipped with EDS analysis system, focused X-ray diffraction (Micro-XRD).Also, the mechanical properties of the weld zone were investigated by using Vickers microhardness test. Microstructure investigation showed that the obtained microstructure from the laser weld of these alloys has a dendritic and non-homogeneous structure. According to XRD analysis, brittle intermetallic compounds such as Fe₂Ti, Cr₂Ti, TiNi₃, and Ti₂Ni wereformed during laser welding in the weld zone. Formation of these brittle intermetallics caused increasing the hardness of the weld zoneabout 800 HV. and decreasing the mechanical properties. Also, Fe₂Ti intermetallic particles mainly formed in the weld region near the NiTi fusion zone which results in stress concentration, micro-cracks formation and dropping joints mechanical properties. Therefore, a suitable modification process is required to control the chemical composition of the weld zone and improving the joint properties of dissimilar laser welded archwires of these alloys.

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Friction stir welding was conducted on AISI 304 austenitic stainless steel sheet with dimensions of
100 mm × 100 mm × 2 mm. The FSW was performed at a welding speed of 150 mm/min and rotational speeds of 400 and 800 rpm. The results showed that high frequency of low angle grain boundaries (LAGBs) were formed through dynamic recovery in the thermo-mechanically affected zone (TMAZ). Higher amount of LAGBs were developed in the TMAZ of welded sample with 800 rpm due to the higher amount of strain and heat generated. High fraction of high angle grain boundaries were formed in the stir zone (SZ) of the welded samples through the occurrence of continuous dynamic recrystallization (CDRX). A very fine microstructure developed in the sampled welded with lower rotational speed. Analysis of texture using {111} Pole figures showed the formation of shear texture components in the SZ of both welded samples. The intensity of the obtained texture for the sample welded with 800 rpm was greater. The formation of shear texture components in the SZ of both samples implied the occurrence of CDRX mechanism

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Single phase brass strips with 2 mm thickness were severely deformed through 1 and 3 cycles of accumulative roll bonding process (ARB). ARB process effectively increased the hardness, yield strength, and the ultimate strength of the processed materials. The hardness of processed material increased from 95 HV in annealed material to 225 HV in 3 cycle ARBed material, and the yielding and ultimate strengths increased more than 5 and 2 times of the annealed sample, respectively. Friction stir welding (FSW) process was successfully conducted on the annealed and ARBed samples to investigate and compare the microstructure and the mechanical properties of the joints obtained in bead on plate configuration. Microstructural observations showed that very fine dynamically recrystallized grains developed in the stir zones (SZs) of all welded samples. Mechanical properties were evaluated by hardness and tensile testing. Hardness test for the ARBed and FS welded samples showed that the hardness value decreased by 110 Hv in the resultant SZs. Results of tensile testing revealed that yield and ultimate strength of the FS welded ARBed samples 1.3 and 1.8 times are greater than that of the annealed FS welded sample .

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