Sirakizhanthanallur Tamilselvan Selvamani

1. The use of Rolled Homogeneous Armor (RHA) steel in defense and structural engineering is mainly associated with the fact that it offers the best hardness, toughness and ballistic impacts resista...

This study involves the use of the resistance spot welding process to join AISI 409M grade ferritic stainless sheet in order to produce high-quality joints as required in the automotive industry. Therefore, by applying response surface methodology with ANOVA and the design of experiment, the process parameters like power, electrode pressure and holding time are optimized to achieve the maximum tensile shear force load in the fabricated joints. The confirmation test effectively proves that it is possible to increase the tensile shear strength of the joint by integrating the optimized welding parameters, and the maximum tensile shear fracture is expected at 12 KN. Finally, the corrosion experiments are conducted on the joint that has been fabricated under optimized condition and the obtained rate of corrosion shows 7.03 mpy, 58.24 mpy, 0.11mpy in neutral, acidic and alkaline solutions respectively. In addition, Optical and Scanning Electron Microscopy are used to analyze the integrity of the joint in order to comprehend its characterization.

The impact of heat input on the hazardous gas emissions of cold metal transfer welded zinc-coated steel joints is the main focus of this study. The bulk formation of fumes during the arc-assisted metal joining process not only affects the characteristics of joints but also, affects the welder’s respiratory systems and environment. Hence, in this research work, using a stack-monitoring kit the welding fumes are collected for various heat inputs and characterized to understand the hazardous emission from zinc-coated steel by the Cold Metal Transfer - 400TPSi advanced technique. The experimental work conducted for the heat input of 0.624 kJ/mm showed superior results for fume formation rate, dust emission rate and emission factor when compared to other heat inputs. In addition, the dust emission rate and fume formation rate increased as the heat input increased. Also, Hazardous gas emissions of CO₂, SO₂, CO, Zinc and the concentration of total dust for the corresponding heat input were found to be within permissible limits. Furthermore, the TEM analysis exhibits that, the particle structure of the fume is agglomerated chains of spherical and faceted morphology. The outcomes prove outstanding results when compared to other welding processes and norms of the NIOSH and ISI 5182 standards.

The goal of this work is to investigate the interface microstructure of the cold metal transfer (CMT) welded dissimilar (AA6061 sheet-galvanized steel sheet) joint at maximum tensile strength (TS) by optimizing the welding parameters using response surface methodology. To attain maximum strength, CMT process variables like voltage (V), current (I), and wire feed rate (WFR) are used to rotate against the output response. The optimized dissimilar joint exhibited a sound appearance without any visible defects and better TS of 141 Mpa as the voltage of 13.9 volts, current of 100 amps, and WFR of 6.2 m/min was given as input. Furthermore, the third intermetallic compound formed at the weld interface at optimized conditions due to controlled heat input was found to be well-controlled and less than 9 um. The weld interface and base metal on the aluminium side of the joints fabricated under various conditions showed larger grains than on the steel side. In addition, the optimized joint was performed to evaluate the corrosion rate, and the results showed 6.8 µA/cm ² . The fracture morphology of the joint reveals that the Fe ₂ Al ₅ compound layer on the aluminium WZ was where joint fractures were most often seen. The aluminium particles on the steel side were found to be unaffected and were observed in the majority of the dissimilar joints at the WZ owing to the intact bonding between the aluminium particles and steel matrix.

Cold Metal Transfer (CMT) arc welding is an updated version of the GMAW process, in which heat input is significantly reduced due to the push-pull action of filler wire feeding during welding. The aluminium alloy sheets are welded by the CMT arc welding process using different heat input levels in this research work. The temperature distribution during welding is experimentally measured with the help of an infrared thermometer, and finite element analysis (volumetric heat source model) is used to predict the temperature distribution, and these results are equated. The influence of heat input on joint characteristics such as bead geometry, microhardness variation, microstructure analysis and tensile properties is also being investigated experimentally. The temperature study reveals that the results of numerical modelling for temperature distribution using various heat inputs were very close to the experimental condition, with a less significant difference ±5. In addition, the well-controlled heat input at 210 J/mm was attributed to eradicating porosity, which was confirmed by Non-destructive evaluation, macrostructure and microstructure analysis. As a result, the joint produced a better tensile strength of 241 MPa due to the achievement of fine grain refinement of 17 µm in the weld zone, reduced heat affect zone, and 6.45% volume fraction of Mg₂Si particles. The intercept length of 18.937 microns is measured as the average value, and the misorientation angle of 25.2922 was also found as the average in the fusion zone, which is more significant when compared to the base metal value of 20 μm.

Friction stir welded (FSW) AA6061 aluminium matrix composites (AMCs) joints with 10% SiC particles were taken under investigation to reduce the corrosion rate. This study integrates the response surface methodology to optimize process parameters of FSW to achieve defect-free AMCs joints. The joint strength of 252 MPa was estimated as maximum tensile strength under rotational speed of 900.38 rpm and thrust force of 20.48 MPa. Furthermore, the turbulence flow of plasticized materials contributes to the restructuring of grains in the weld zone, and it is mainly influenced by the tool rotation. The cyclic potentiodynamic polarization test has been carried out in the different zones of friction stir welded AMCs joints using a 3.5% sodium chloride (NaCl) solution that is aerated naturally at 25 °C. It was seen that the corrosion polarization value of the Heat affected zone (HAZ) is 400 μ A cm ² , the un-welded aluminium matrix composite is 345 μ A cm ² , and the stir zone is 751 μ A cm ² at the optimized conditions. The corrosion study reveals that the SiC reinforcement was a suspicious agent that propagated the pits in larger and deeper sizes when the various zones of the welded joint were exposed to electrochemical studies.

Cold Metal Transfer welding is a predominant process for joining the Aluminium and Low Carbon Steel (LCS) dissimilar joints with enhanced properties. In addition, these joints have vast application in various simulated industrial environmental conditions. However, the formation of thick intermetallic layers during welding over these joints leads to invoking the corrosion attack and causing a catastrophic failure that is the primary concern in life prediction of the joint. Hence, the corrosion behaviour of AL-LCS dissimilar butt joint exposed in the simulated industrial environment has been studied experimentally and it has been compared with the Cold Metal Transfer (CMT) welded aluminium and LCS similar joints. The potentiodynamic polarization and the electrochemical impedance spectroscopy were carried out in 3.5% aggressive sodium chloride medium with varying benzotriazole corrosion inhibitor with varying the concentrations like 10 ppm, 15 ppm and 20 ppm. The results showed that the corrosion resistance behaviour of CMT welded dissimilar joints are increased with increasing inhibitor concentration. The inhibitor showed effective performance, and the efficiency is also found to be 78–80% at 20ppm, which revealed the enhanced corrosion resistance of dissimilar metal joints in simulated industrial conditions. Finally, the dissimilar joints are characterized by sophisticated analytical techniques.

The present investigation demonstrates the friction welding of the AA6063-T6 joint to attain the maximum tensile strength by optimizing the parameters (friction load, friction time, and upset load) through response surface methodology. BoxBehnken design is a subset of the response surface methodology (RSM) which was employed to design the experiment numbers, and it was restricted to 15 sets. Furthermore, the inbuilt ANOVA technique was used to obtain the statistical data for the developed numerical model, and the relationship among the parameters against the output response (tensile strength) was interpreted by using the statistical data. Following this, the mechanical and metallurgical studies were done on the optimized conditions using appropriate testing and characterization equipment. The optimized conditions such as friction load (f) of 3kN along with friction time (t) of 6s and an upset load of 2.5kN are given as input to attain the highest TS of 248MPa. Moreover, the interface between the weld zone and the base metal of the joint was found to be broken during the tensile test when the friction load was given as 3kN and 4kN, while the fracture location of the joint was found in the weld zone at the lower friction load of 2kN. Finally, the acquired results of the optimized friction welded conditions on the AA6063-T6 joint were discussed to justify the statistical data of the numerical model, and the same results were compared to the previous research studies.

During welding, the heat input is a critical parameter in determining the quality of the joints welded by any welding process. In the case of dissimilar welding, as dissimilar metals have significant differences in melting point, it is challenging to achieve an adequate joint. The emerging cold metal transfer welding process can resolve it effectively by controlling the heat while joining dissimilar metals. Therefore, in this research work, Aluminum-galvanized steel dissimilar joints were fabricated using varying heat inputs and their mechanical, metallurgical, and corrosion properties were evaluated. Furthermore, the second-phase formation at the weld interface has been investigated, and corrosion behavior is analyzed using electrochemical techniques in a 0.1% sodium chloride environment. The Tafel polarization and electrochemical impedance spectroscopy studies reveal it improved corrosion resistance due to an increase in heat input. The reduced solidification defects and the establishment of an appropriate intermetallic layer thickness with a suitable microstructure at the interface are the reasons for the improved corrosion resistance and strength of the dissimilar joints.

The versatile aluminium alloys and steel are being used in automotive engines (exhaust systems), pressure vessels (flanges), turbine rotors, boilers (bonnet) and in many applications. The collective effect of these two metals created a revolution and are being utilized in most of the sectors wherein joining of these two dissimilar materials are always a major challenge faced by the manufacturers. Initially, the rivets were widely used for joining dissimilar materials owing to easy installation and flexibility, but the joint interlock fails and sudden ruptures occurred when exposed to higher load. Hence, numerous welding processes like metal inert gas welding, friction stir welding, friction stir spot welding, advanced laser welding, advanced cold metal transfer welding and hybrid welding techniques have been introduced in order to conquer the above problem because of residual stresses, cracks, distortion, and undercuts. Moreover, an appropriate standardization with controlled process inputs is still an uncertainty in joining the dissimilar materials. Hence, a detailed review on joining the dissimilar metals based on aluminium alloy and steel by various welding processes and influence of their parameters on the properties have been summarized in detail which would be a reference for manufacturing industries in the coming decades.