Microstructural Characterization and Mechanical Properties of Laser Beam-Welded Dissimilar Joints between A6000 Aluminum Alloy and Galvanized Steel

This paper presents the laser beam welding process of a lap joint between galvanized steel (Z225) and an aluminum alloy (A6000) from an IPG fiber laser. Welding of steel to aluminum has become popular in the automotive industry as a means of reducing the total vehicle body mass. This approach reduces fuel consumption and, ultimately, carbon emissions. Laser welding parameters used to control heat input for the study were laser power ranging between 800 and 1200 W, as well as laser welding speeds between 2 and 4 m/min. Distinct features of the dissimilar joints were microscopically examined. The SEM-EDS technique was employed to study the intermetallic phases along the Fe-Al interface. The outcome revealed the presence of “needle-like phases” and “island-shaped phases” at high heat inputs. Traces of both Fe2Al5 and FeAl3 phases were detected. For low heat input, there was evidence of insufficient fusion. Weld width was influenced by welding parameters and increased with an increase in heat input. Mechanical properties of the joints indicated that the microhardness values of the weld joints were higher than those of both base metals. The maximum tensile shear strength obtained was 1.79 kN for a sample produced at 1200 W and 3 m/min.

Advances in joining technologies for the innovation of 21st century lightweight aluminium-CFRP hybrid structures

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.

Water lifting and outflow gain of kinetic energy in tropical cyclones

While water lifting plays a recognized role in the global atmospheric power budget, estimates for this role in tropical cyclones vary from no effect to a major reduction in storm intensity. To better assess this impact, here we consider the work output of an infinitely narrow thermodynamic cycle with two streamlines connecting the top of the boundary layer in the vicinity of maximum wind (without assuming gradient-wind balance) to an arbitrary level in the inviscid free troposphere. The reduction of a storm’s maximum wind speed due to water lifting is found to decline with increasing efficiency of the cycle and is about 5% for maximum observed Carnot efficiencies. In the steady-state cycle, there is an extra heat input associated with the warming of precipitating water. The corresponding positive extra work is of an opposite sign and several times smaller than that due to water lifting. We also estimate the gain of kinetic energy in the outflow region. Contrary to previous assessments, this term is found to be large when the outflow radius is small (comparable to the radius of maximum wind). Using our framework, we show that Emanuel’s maximum potential intensity (E-PI) corresponds to a cycle where total work equals work performed at the top of the boundary layer (net work in the free troposphere is zero). This constrains a dependence between the outflow temperature and heat input at the point of maximum wind, but does not constrain the radial pressure gradient. We outline the implications of the established patterns for assessing real storms.

Effect of Heat Input on LMHMW Joint of Carbon Steel

Laser-MIG hybrid multi-layer welding (LMHMW) technology has been employed in paraxial configuration with laser leading for the welding of 20 mm thick Q235 carbon steel plates to exploit the hybridization effect that addresses the shortcomings of the individual process as well as to compliment their merits. The bilateral effects of arc augmented laser welding have resulted in complete joint penetration, process efficiency, stability and gap bridge ability. Samples welded under varying heat inputs in multiple passes have been analyzed for their microstructure evaluation using an optical microscope followed by tensile and Vickers hardness testing in various regions of the weld zones. This process was conducted to characterize the effect of heat input on the mechanical properties of the welded joints. The experimental results illustrate that different heat inputs have significant effects on the microstructure, heat affected zone width and mechanical properties of welded joints. The microhardness near the fusion line decreases dramatically due to the influence of the phase transformation process, and the highest microhardness value is obtained in the center of the weld seam. By using reasonable process parameters, the strength of the welded joint can obtain 458.5 MPa.

On the Effect of Heat Input and Interpass Temperature on the Performance of Inconel 625 Alloy Deposited Using Wire Arc Additive Manufacturing–Cold Metal Transfer Process

Relatively high heat input and heat accumulation are treated as critical challenges to affect the qualities and performances of components fabricated by wire arc additive manufacturing (WAAM). In this study, various heat inputs, namely 276, 552 and 828 J/mm, were performed to fabricate three thin-wall Inconel 625 structures by cold metal transfer (CMT)-based WAAM, respectively, and active interpass cooling was conducted to limit heat accumulation. The macrostructure, microstructure and mechanical properties of the produced components by CMT were investigated. It was found that the increased heat input can deteriorate surface roughness, and the size of dendrite arm spacing increases with increasing heat input, thus leading to the deterioration of mechanical properties. Lower heat input and application of active interpass cooling can be an effective method to refine microstructure and reduce anisotropy. This study enhances the understanding of interpass temperature control and the effectiveness of heat inputs for Inconel 625 alloy by WAAM. It also provides a valuable in situ process for microstructure and mechanical properties’ refinement of WAAM-fabricated alloys and the control of heat accumulation for the fabrication of large-sized structures for future practical applications.

Investigation on Impact of Heat Input on Microstructural, Mechanical, and Intergranular Corrosion Properties of Gas Tungsten Arc-Welded Ti-Stabilized 439 Ferritic Stainless Steel

In the present study, gas tungsten arc welding was employed to weld Ti-stabilized 439 ferritic stainless steel using 308L austenitic stainless steel filler electrode with varying heat input, i.e., low heat input (LHI) and high heat input (HHI). The optical microstructure revealed the formation of retained austenite (RA) and ferrite in the weld zone (WZ), whereas the peppery structure consisting of chromium-rich carbides were observed in the heat-affected zone for both the weldments. The volumetric fraction of RA was calculated using X-ray diffraction analysis. The RA’s content decreased, whereas grain size in WZ increased with an increase in heat input. The local misorientation and grain boundary distribution in the welded region was investigated by electron backscattered diffraction. The LHI weldment depicted the higher micro-hardness and tensile strength attributed to the higher content of RA as compared to HHI; however, the opposite trend was observed for the intergranular corrosion resistance.

Pulse spray gas metal arc welding of advanced high strength S650MC automotive steel

With an increasing demand for safer and greener vehicles, mild steel and high strength steel are being replaced by much stronger advanced high strength steels of thinner gauges. However, the welding process of advanced high strength steels is not developed at the same pace. The performance of these welded automotive structural components depends largely on the external and internal quality of weldment. Gas metal arc welding (GMAW) is one of the most common methods used in the automotive industry to join car body parts of dissimilar high strength steels. It is also recognized for its versatility and speed. In this work, after a review of GMAW process and issues in welding of advanced high strength steels, a welding experiment is carried out with varying heat input by using spray and pulse-spray transfer GMAW method with filler wires of three different strength levels. The experiment results, including macro-microstructure, mechanical properties, and microhardness of weld samples, are investigated in detail. Very good weldability of S650MC is demonstrated through the weld joint efficiency > 90%; no crack in bending of weld joints, or fracture of tensile test sample within weld joint or heat affected zone (HAZ), or softening of the HAZ. Pulse spray is superior because of thinner HAZ width and finer microstructure on account of lower heat input. The impact of filler wire strength on weldability is insignificant. However, high strength filler wire (ER100SG) may be chosen as per standard welding practice of matching strength.