Ultrasonic additive manufacturing of nanocrystalline laminated composites

Ultrasonic additive manufacturing has been used to fabricate laminated composites of commercially pure aluminum and a nanocrystalline nickel–cobalt (nc-NiCo) alloy. The nc-NiCo alloy would not weld to itself but readily welded to aluminum. Thus, by alternating between foils of nc-NiCo and Al, we achieved multi-material laminates with strong interlayer bonding. Electron microscopy showed that the nanoscale grain structure of the nc-NiCo was preserved during deposition and that the nc-NiCo/Al weld interface was decorated with comminuted surface oxides as well as Al–Ni–Co intermetallics. These findings are considered in light of process models of junction growth, interdiffusion, and grain growth, which together reveal how the different pressure- and temperature dependences of these phenomena give rise to a range of processing conditions that maximize bonding while minimizing coarsening and intermetallic formation. This analysis quantitatively demonstrates that using a soft, low melting point interlayer material decouples junction growth at the weld interface from grain growth in the nc-NiCo, expanding the range of optimal processing conditions. Graphical abstract

Development and Evaluation of the Ultrasonic Welding Process for Copper-Aluminium Dissimilar Welding

The demand for joining dissimilar metals has exponentially increased due to the global concerns about climate change, especially for electric vehicles in the automotive industry. Ultrasonic welding (USW) surges as a very promising technique to join dissimilar metals, providing strength and electric conductivity, in addition to avoid metallurgical defects, such as the formation of intermetallic compounds, brittle phases and porosities. However, USW is a very sensitive process, which depends on many parameters. This work evaluates the impact of the process parameters on the quality of ultrasonic spot welds between copper and aluminium plates. The weld quality is assessed based on the tensile strength of the joints and metallographic examination of the weld cross-sections. Furthermore, the welding energy is examined for the different welding conditions. This is done to evaluate the influence of each parameter on the heat input resulting from friction at the weld interface and on the weld quality. From the obtained results, it was possible to optimise parameters to achieve satisfactory weld quality in 1.0 mm thick Al–Cu plate joints in terms of mechanical and metallurgical properties.

Investigation On Mechanism of Ultrasonic Welding AZ31B / 5052 Joint With Laser Texturing On Mental Surface

The ultrasonic welding was carried out to improve the quality of dissimilar Al/Mg alloys joint. The effects of laser texturing on the microstructure and mechanism of AZ31B/5052 joint connected by ultrasonic welding were also investigated. A series of laser texturing experiments on Al alloy (5052) and Mg alloy (AZ31B) were performed to determine the process parameters and their ef-fect on ultrasonic weld quality, especially on weld strength. Little effect was attained by opti-mizing welding parameters in improving mechanical properties. Both welding parameters and different texture pattern were investigated to obtain good weld quality. The connection mecha-nisms of joints were discussed based on the analysis of weld interface morphology, microstruc-ture evolution. Mechanical analysis of particle and movement of material atoms were analyzed in the study to explain the connect mechanism. The results show that the better lock-interface and lager lap shear strength were attained by laser texture addition and optimal welding parameters. Compared with the untextured joint, swirling bonding interface was obtained after the laser tex-ture. The laser texture with grid pattern was found to raise the strength up to 26% higher maxi-mum tensile-shear load than the joints obtained with the untextured surface.

The Effect of Preheating Current on the Melting Behavior of Bolt Projection Welding of Al-Si Coated Hot-Stamped Boron Steel

This study evaluated the effect of preheating on early stage melting behavior of a Al-Si coated hot stamped boron steel bolt during projection welding. A large amount of heat was generated in the early stage of projection welding. Because of the large heat generation, a rapid collapse of the projection occurred and a molten coating layer remained on the interface of the welded part. This caused welding defects such as expulsion and porosity. However, preheating helped remove the molten Al-Si coating layer by pushing it out toward the outer edge of the molten pool. This suggests that preheating can effectively minimize or remove the molten coating layer within the weld. Preheating also prevented the rapid collapse of the projection by partially melting the projection, and thus improving the contact area. These phenomena can prevent the concentration of current density at the weld interface and hence decrease heat generation. Finally, the preheating current improved nugget quality by promoting the stable growth of the melted metal and by preventing expulsion and porosity.

Dissimilar Rotary Friction Welding of Inconel 718 to F22 Using Inconel 625 Interlayer

Dissimilar metal joining has always been a challenging task because of the metallurgical incompatibility and difference in melting points of alloys being joined. Diffusion and mixing of alloying elements from dissimilar base metals at the weld often cause unwanted metallurgical changes resulting in unsuccessful welds or underperformance of the weldment. Solid-state dissimilar friction welds of Inconel 718 and F22 were prepared in this study with an Inconel 625 interlayer to address the carbon enrichment of Inconel 718 during the welding. Defect-free rotary friction welds were produced in this study. Microstructural and mechanical properties investigation of the weldments and base metals was carried out, and results were analysed. Intermixing zone was observed at the weld interface due to the softening of the metal at the interface and rotatory motion during the welding. The high temperatures and the plastic deformation of the intermixing zone and thermo-mechanically affected zone (TMAZ) resulted in the grain refinement of the weld region. The highest hardness was observed at the Inconel 718/F22 weld interface due to the plastic strain and the carbon diffusion. The tensile specimens failed in the F22 base metal for the weld prepared with and without the Inconel 625 interlayer. Inconel 718/F22 welds exhibited lower toughness values compared to the Inconel 718/F22 welds prepared with Inconel 625 interlayer.

Microstructure and Mechanical Property Correlation Between Rotary Friction Welded Nitinol–Nitinol Joints

In the present study, a rotary friction process was used to join nitinol in a similar welding combination. Macro- and microstructure characteristics of the weld zone were compared with adjacent zones and the base metal. The hardness and tensile properties of the joints were evaluated, and the results were discussed in relation to the weld microstructure. The weld macrostructure revealed a uniform flash around the circumference of the weld. The optical microstructure of the welded sample revealed fine recrystallized grains at the weld interface due to heavy deformation followed by dynamic recrystallization. The phase transformation behavior of the base metal and welded samples was studied by using a differential scanning calorimeter (DSC). The drift in phase transformation temperatures after rotary friction welding may be attributed to fine grain formation at the weld interface. Friction welded samples exhibited improved yield strength and hardness values compared to the base metal due to grain refinement at the weld interface.

Study on notch tensile properties of Magnetically Impelled Arc Butt (MIAB) welded carbon steel tubes

Magnetically Impelled Arc Butt (MIAB) welding is a pressure welding process that uses the circumferential rotating arc to cause uniform heating of the faying surfaces. In this work, notched tensile testing of MIAB welded Carbon steel was carried out to determine the notch sensitivity of Thermo-Mechanically Affected Zones (TMAZ) and to compare the notch tensile property of these zones with the base metal property. In MIAB welding, after sufficient melting of the faying surface, a short pulse of high current is applied to expel the molten metal and impurities from the interface before welding. Insufficient expulsion and formation of Light Band (LB) zone at weld interface resulted in lower Notch Tensile Strength (NTS). Incomplete expulsion with lower upset current at the weld interface contributes to lower Normalized Notch Strength Ratio. Instead higher upset current contributed to higher NTS due to complete expulsion and stronger acicular ferrite formation. Other TMAZs away from the weld interface showed higher notch tensile strength with Notch Strength Ratio (NSR) and Normalized Notch Tensile Strength Ratio (NTSN) greater than unity.

Comparative assessment on weldability of Al 6061 to polycarbonate for dissimilar sheets placement in friction stir lap welding using sensor signals

The thermoplastic polymers and precipitation hardened aluminium alloys are highly popular in the aerospace and automobile sectors as a replacement of metallic materials to improve the strength to weight ratio. Thus, the unlike aluminium alloy to polycarbonate assembled structures are often necessary for which mechanical fastening and adhesive bonding are the primary methods for joining as fusion welding processes are inadequate. However, the dissimilar joint efficiency is found to be less. Thus, the ultrasonic and friction welding processes are developed. The friction stir welding is one such advanced material stirring technique without any melting of base materials. The present work addresses metallic aluminium (Al6061) to polycarbonate sheet materials joining using friction stir welding in overlap configuration using tapered H13 tool steel. The thrust force with associated tool stirring torque has been acquired in real time during plunging followed by welding phase. The weld bead profile with respective force-torque signals was analysed for the process monitoring. The tensile test has been carried out on the lap welds. The weld interface of the unlike sheets have also been scrutinised. Initially, the aluminium sheet was partially overlapped on polycarbonate for the parametric study. The highest joint efficiency was found to be 40.2% at 1400 rpm tool rotational speed and 75 mm/min traverse speed due to improper material mixing at the weld interface. Therefore, the feasibility of the process have been tested by placing thermoplastic polycarbonate over aluminium alloy through which the joint efficiency was further improved (48.57%) at comparatively low tool rotational speed (1100 rpm) with lower welding speed (55 mm/min) as the minute metallic particles uniformly mixed with melted and solidified polycarbonate due to more uniform torque in the welding phase. The tool stirring torque and axial thrust was found to be higher in this overlap position.

Study on Effect of Laser Process Parameters on Laser Transmission Weld Parameters using ANSYS

In recent years, a mode of welding that has garnered a considerable amount of interest is the laser transmission welding of thermoplastics. Laser transmission welding is now being used as an alternative to adhesives to join two thermoplastics. In this study, a finite element model has been developed to simulate the laser transmission welding of polypropylene. The movement of the laser beam was done using a Moving Heat Source in Ansys®. Process parameters namely laser power, welding speed, and the number of passes have been studied in order to investigate their effects on the temperatures and the weld widths achieved during welding. It was found that an increase in the laser power had a positive effect on the maximum temperature at the weld interface as well as the weld width. Similarly, an increase in the welding speed had a negative influence on the maximum temperature at the weld interface as well as the weld width.