Friction Stir Welded AA5052-H32 under Dissimilar Pin Profile and Preheat Temperature: Microstructural Observations and Mechanical Properties

In order to meet the escalating demand in the shipbuilding business, suitable materials with enhanced qualities are required to maximize ship cargo while reducing fuel consumption. Aluminum (Al) and its alloys are competing contenders for use in a variety of complicated ship structures. The major challenge to enhancing joint quality and performance is the quest for a viable and efficient FSW parameter. The main focus of this study was to critically explore the effect of the tool pin profile and the preheat temperature used during the friction stir welding of AA 5052-H32 on its mechanical properties and weld microstructure characteristics. There are three pin profile variations, including samples that were cylindrical, samples with two flat sides, and samples with three flat sides, all of which were investigated in different preheat temperatures (150–300 °C). The results that were obtained during macrographic observation showed that tunnel defects were visible in the cylindrical and two-flat-sided pin profile designs. During observations of the microstructure, it was observed that the grain size became finer and smaller in the weld nugget compared to in the heat affected zone (HAZ) and thermo-mechanically affected zone (TMAZ) regions due to dynamic recrystallization. However, at the 300 °C preheat variation, the grain size appeared to be larger due to the slower cooling rate, causing a decrease in the mechanical properties of the samples. The results of the physical tests determined that the preheat temperature caused an increase in the mechanical properties until 250 °C, at which point the three-flat-sided pin profile tool demonstrated superior mechanical properties compared to the tools with a cylindrical design; a 12.2% tensile strength increase, a 15.3% and 9.4% face and root bending increase, and an 11.2% hardness increase were observed.

Experimental and Numerical Analysis of Refill Friction Stir Spot Welding of Thin AA7075-T6 Sheets

The refill friction stir spot welding (refill FSSW) process is a solid-state joining process to produce welds without a keyhole in spot joint configuration. This study presents a thermo-mechanical model of refill FSSW, validated on experimental thermal cycles for thin aluminium sheets of AA7075-T6. The temperatures in the weld centre and outside the welding zone at selected points were recorded using K-type thermocouples for more accurate validation of the thermo-mechanical model. A thermo-mechanical three-dimensional refill FSSW model was built using DEFORM-3D. The temperature results from the refill FSSW numerical model are in good agreement with the experimental results. Three-dimensional material flow during plunging and refilling stages is analysed in detail and compared to experimental microstructure and hardness results. The simulation results obtained from the refill FSSW model correspond well with the experimental results. The developed 3D numerical model is able to predict the thermal cycles, material flow, strain, and strain rates which are key factors for the identification and characterization of zones as well for determining joint quality.

Study On The Steel-Aluminum Plastic Clinching of The Inclined Wall Die

Aiming at the problems of low strength and unsatisfactory connection quality of plastic clinching of heterogeneous lightweight materials for the cars body, the Q235 steel sheets, and 5052 aluminum alloy sheets were taken as the research objects, and the inclined wall die for plastic clinching was designed based on the deformation and flow characteristics of sheets in the plastic clinching process. The elastic-plastic finite element numerical simulation and experimental research were used to analyze the plastic clinching process of the inclined wall die, and the failure mode and mechanism of the clinching joints in the shear and peel experiment were deeply studied. The results show that the inclined wall die can effectively increase the interlock value of the joints and reduce the maximum joining force during the clinching process under the condition of ensuring the neck thickness of the joints. When the inclined wall angle α increases from 90° to 100°, the interlock value increases by 38.9%, and the maximum joining force decreases by 8.3%. The influence of inclined wall structure on joint quality can be divided into extrusion stage, radial inflow stage, and stability stage. The comparison between the clinching experiment and the finite element results shows that the two results are in good agreement, which proves that the finite element model of plastic clinching of inclined wall die has a high degree of credibility, and verifies the feasibility of practical application of inclined wall die. Finally, under shear and peel loads, the main failure mode of the joints is separation failure.

A Recent Progress in Performance and Property Improvement in Underwater Welding

Underwater welding is the process of connecting materials underwater in the presence of water. It is used to maintain and improve the structure in marine and offshore applications. It's utilized for underwater pipeline maintenance, submerged offshore oil drilling, and ship repairs. It can also be found in nuclear power plants and deep-sea mining. Underwater welding is divided into two categories dry welding and wet welding. Dry welding entails enclosing the weld zone in a hyperbaric tank filled with a gas mixture and welding at the prevailing pressure. Wet welding is a type of welding that uses waterproof electrodes and is done directly on the component to be welded. The major benefit of this welding is its simplicity and cost effectiveness, but we can't obtain high weld quality as easily as we can with dry welding. Dry welding, on the other hand, may provide high weld quality, but it is a time-consuming procedure that needs the welder to secure the region with the hyperbaric vessel, and it is also a costly method. Underwater welding has a number of issues, including bubble arc generation, cold cracking, microstructural deformation, and more. We attempted to bring together the most recent developments in the field of underwater welding. We've outlined several techniques that were used to improve welding characteristics as well as important issues that must be addressed. This review article may be used to figure out what measures need to be taken to enhance the underwater weld joint quality. Keywords: Underwater welding, underwater wet welding, underwater dry welding, hyperbaric vessel, underwater welding development

Investigation of ultrasonically welded thermoplastic composite joints using netlike energy directors

This paper proposes a netlike energy director (ED) made of carbon fiber-reinforced thermoplastic (CFRP) composites to improve the ultrasonic welding energy efficiency. To explore the benefits of using netlike EDs, the joint qualities with flat EDs and without EDs are included for references. Also, the influence of the netlike ED geometry (i.e., hexagonal nets with different side lengths and thicknesses) on weld attributes and joint quality are investigated in terms of joint cross-sectional microstructure, fracture morphology, and maximum shear load. It is found that for both the netlike and flat EDs, the welding process can be accelerated compared to the one without EDs, which is caused by the concentration of welding energy into the expected welding region and the avoidance of welding edges introduced by surface curvature. Meanwhile, compared with flat EDs, the maximum shear loads of the joints with netlike EDs are improved, introduced by the decrease of the contact area and consequent higher cyclic strain, resulting in more melted materials during the ultrasonic welding process. However, with the increasing of the netlike ED thickness, more porosities are generated in the welding layer leading to reduced bonded region and decrease of the maximum shear load. From the joint fracture morphology analysis, it is found that the netlike EDs introduces carbon fibers in the welding layer, and the fracture modes include fiber-matrix debonding and fiber pull-out in addition to polymer fracture, confirming the feasibility of improving joint quality by introducing CFRP netlike EDs.

Microstructural and Mechanical Behaviors of Friction Stir Welded Dissimilar AA6082-AA7075 Joints

In this research, microstructural events and mechanical behaviors in dissimilar friction stir welding (FSW) of aluminium (Al) alloy AA6082-AA7075 joints have been evaluated to apply aerospace, defense, and military sectors. FSW parametric effects have a more significant impact on the mechanical performances and microstructure of produced joints. FSW tool rotational speed, welding speed, and tool plunge speed were chosen to make the weld joints. The rotational tool speeds of 1600 rpm and 2300 rpm, welding speeds of 40 mm/min and 60 mm/min, and tool plunge speeds of 20 mm/min and 30 mm/min were set as the upper and lower limits. A constant axial force of 5 kN was maintained throughout the joint fabrication process. A taper pin-profiled tool was utilized to produce the butt welded joints. Mechanical properties of microhardness, tensile strength, yield strength, elongation, and bending strength of the joints were analyzed. The response of the stir zone microstructure to processing parameters was evaluated using optical microscopy (OM) and fractographic analysis of a tensile specimen shown by scanning electron microscope (SEM). The weld joints produced at 2300 rpm, tool traveling rate of 40 mm/min, and tool plunge speed of 30 mm/min showed the greatest tensile strength of the 191 MPa hardness of 145 Hv at the weld center and also the maximum bending strength of 114.23 N/mm2 was achieved. The lowest bending strength of 25.38 N/mm2 was obtained at 1600 rpm with 60 mm/min due to inappropriate mixing of the base metals and poor joint quality. Furthermore, this study revealed that a higher tool plunge speed facilitates the formation of equiaxed grains in the thermomechanically affected zone (TMAZ) on the advancing side (AS). Additionally, the increment in tool rotational speed significantly improved the tensile strength, weld joint quality, and joint efficiency.