The study aimed at investigating the microstructure and mechanical properties of Neodymium-Doped Yttrium Aluminum Garnet (Nd:YAG) laser welded high strength low alloy (HSLA) SA516 grade 70 boiler steel. The weld joint for a 4 mm thick plate was successfully produced using minimum laser power of 2 kW by employing a single pass without any weld preheat treatment. The micrographs revealed the presence of martensite phase in the weld fusion zone which could be due to faster cooling rate of the laser weldment. A good correlation was found between the microstructural features of the weld joints and their mechanical properties. The highest hardness was found to be in the fusion zone of cap region due to formation of martensite and also enrichment of carbon. The hardness results also showed a narrow soft zone at the heat affected zone (HAZ) adjacent to the weld interface, which has no effect on the weld tensile strength. The yield strength and ultimate tensile strength of the welded joints were 338 MPa and 549 MPa, respectively, which were higher than the candidate metal. These tensile results suggested that the laser welding process had improved the weld strength even without any weld preheat treatment and also the fractography of the tensile fractured samples showed the ductile mode of failure.

The mechanism of austenite reversion in 18 Ni Co‐free maraging steel (250 grade) has been established by conducting extensive X‐ray diffraction (XRD) and transmission electron microscopy (TEM) under differently aged conditions. It has been proposed that contrary to the precipitate dissolution mechanism suggested for the initiation of austenite reversion in 18Ni‐8Co‐5Mo type maraging steels, the initiation of transformation of martensite to austenite in this type of maraging steel is due to the diffusion of Ni from matrix to the dislocations and other defect structures on prolonged/high temperature ageing. This results in local enrichment of Ni which lowers both AS and MS temperatures of the region. Lowering of these transformation temperatures is responsible for the early reversion of martensite to Ni‐enriched stable austenite which, on subsequent cooling to room temperature, does not transform back to martensite.

In this research work, the weldability of low alloyed AISI 4340 aeronautical steel and AISI 304L austenitic stainless steel joined by continuous current (CC) and pulsed current (PC) gas tungsten arc welding (GTAW) techniques, using ER309L and ERNiCr-3 filler metals was investigated. The main focus of the study involves the investigation on the effect of continuous and pulsed current mode of GTA welding process on the metallurgical and mechanical properties of these dissimilar weldments. Microstructure studies revealed the formation of different zones across the weldments, vis-à-vis martensite at the HAZ of AISI 4340, vermicular δ -ferrite /ferrite stringers at the HAZ of AISI 304L, pearlite colonies at the parent metal of AISI 4340 and equi-axed cellular and/or columnar dendrites at the weld zone. Tensile results showed that current pulsing accrued better tensile properties. The structure -property relationships of these weldments were established based on the current modes employed by utilizing combined techniques of optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

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This investigation has been performed to characterize the microstructure and mechanical properties of the GTA and PCGTA welded dissimilar combinations of Inconel 625 superalloy and AISI 304 austenitic stainless steel. These welds were obtained by employing ERNiCrMo-3 filler metal. The weldments were characterized by the combined techniques of optical microscopy and SEM/EDAX analysis. Hardness and tensile studies were conducted to assess the mechanical properties of the weldments. Tensile studies showed that the fracture had occurred at the parent metal of AISI 304 side in both the cases.KEY WORDS: gas tungsten arc welding; pulsed current gas tungsten arc welding; alloy 625; austenitic stainless steel AISI 304; filler metal.

In the twenty-first century, the application of carbon fiber reinforced polymer (CFRP) materials in the vehicle industry are growing rapidly due to lightweight, high specific strength, and elasticity. In the automobile and aerospace industries, CFRP needs to be joined with metals to build complete structures. The demand for hybrid structures has prompted research into the combination of CFRP and metals in manufacturing. Aluminium and CFRP structures combine the mechanical properties of aluminium with the superior physical and chemical properties of CFRP. However, joining dissimilar materials is often challenging to achieve. Various joining technologies are developed to produce hybrid joints of CFRP, and aluminium alloys include conventional adhesives, mechanical and thermal joining technologies. In this review article, an extensive review was carried out on the thermal joining technologies include laser welding, friction-based welding technologies, ultrasonic welding, and induction welding processes. The article primarily focused on the current knowledge and process development of these technologies in fabricating dissimilar aluminium and CFRP structures. Besides, according to Industry 4.0 requirements, additive manufacturing-based techniques to fabricate hybrid structures are presented. Finally, this article also addressed the various improvements for the future development of these joining technologies. Ultrasonic welding yields the maximum shear strength among the various hybrid joining technologies due to lower heat input. On the other hand, laser welding produces higher heat input, which deteriorates the mechanical performance of the hybrid joints. Surface pretreatments on material surfaces prior to joining showed a significant effect on joint shear strength. Surface modification using anodizing is considered an optimal method to improve wettability, increasing mechanical interlocking phenomena.

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