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The evolution of processing parameters by varying tool eccentricity in AA6061 alloy friction stir welding was examined using a combination of detailed force/torque measurements and thermal history as well as high-speed camera (HSC) observations. Tri-axial forces show larger oscillations during the steady-state phase of welding if the tool eccentricity is increased. However, the tool torque remains similar for up to 0.4 mm eccentricity versus the aligned tool even with varying weld speed. In situ HSC observation indicates that tool eccentricity is reduced during the welding process for larger eccentric setups. Stir zone thermal measurements reveal that the temperature peaks and stabilizes near the solidus temperature of the AA6061 base material.

The increasing demands in productivity and reliability in welding have led to the development of newer welding processes. These processes frequently have superior deposition rates; however, they might lead to a wider heat-affected zone (HAZ) which might impair their mechanical properties. Here, a promising process termed the double cold wire gas metal arc welding (DCW-GMAW) is evaluated, offering higher deposition rates via feeding two cold wires into the weld pool to improve productivity. In contrast to similar processes, the HAZ of DCW-GMAW welds are smaller than gas metal arc welding (GMAW) welds. This work reports a preliminary assessment of the feasibility of the process in terms of electrical arc characteristics and stability. High-speed video acquisition was used to analyze the metal transfer across the arc. Finally, standard metallographic techniques and Vickers hardness were used to assess the weld cross sections and microstructures. The results demonstrate the feasibility of DCW-GMAW based on the process stability at different cold wire feed rates while also offering high deposition (high productivity) of weld deposits with desirable hardness due to increased acicular ferrite content.

Statistical models were developed to study the effect of gas metal arc welding process parameters (i.e., wire feed speed, voltage, travel speed, and shielding gas chemistry) on the resultant weld bead width, penetration, and reinforcement height, using a factorial design of experiment. Analysis of variance (ANOVA) indicated that the weld width depended on voltage, travel speed, gas type, and the interactions between these factors. The weld penetration depended only on wire feed speed and gas type, as well as the two-way interactions of wire feed speed with travel speed and gas type. Reinforcement height depended on travel speed, wire feed speed, and their two-way interactions with gas type. Residual analysis revealed that all assumptions inherent in the regression analysis were satisfied over the range of welding parameters considered in this study. The predictive power of the statistical models was validated using intermediate process parameter values in the experimental design, and it was found that predicted values were mainly in agreement with the measured values for a 95% prediction interval.

Dissimilar friction stir welding of AA5052-AA6061 was conducted to assess the effect of material positioning on the welds produced using tools with predetermined eccentricity. Microstructural observation, thermal cycle measurement, and mechanical property evaluation was subsequently conducted. Evidence shows that AA6061 is better suited to welding while placed on the advancing side (AS), since better transverse tensile strength (up to 215 MPa) and elongation (up to 7.6%) can be achieved. On the other hand, higher peak temperatures were generally observed in the AS regardless of base material positioning, where peak temperatures of more than 350 °C were recorded by the thermocouple located closest to the stir zone. Metallurgical analysis reveals that tool eccentricity enhances the AS material flow in the stir zone but limits dissimilar material mixing.

Gas metal arc welding (GMAW) with direct current electrode negative (DCEN) can offer some advantages over direct current electrode positive (DCEP) welding, such as a higher electrode melting rate and lower heat input imposed onto the workpiece. Despite these advantages, DCEN is not commonly used in field applications due to instabilities caused by arc climb and the volatile repelled metal transfer mode across the arc. This work reports a comparison between DCEP and DCEN in natural spray transfer mode using a welding power source operating in constant voltage (CV). It aims to assess the feasibility of DCEN in cold wire gas metal arc welding (CW-GMAW) comparing the results obtained in DCEN with previous results obtained in DCEP for the same welding parameters. During experiments, the current and voltage were acquired with synchronized high-speed video to study the arc dynamics. Bead-on-plate welds were deposited onto AISI 1020 steel flat bars. Three cross sections for each bead were cut and metallographically examined to compare bead geometry. Results suggest that the cold wire feeding can suppress arc climb in DCEN welding, consequently improving the arc stability and bead finish. Moreover, the DCEN welds suggest that the heat transferred to the weld pool is fundamental to accommodate high feed rates of cold wire. Lastly, the cross section results show that penetration, dilution, and HAZ area are lower in DCEN than in DCEP mode.

In this research, the printability of Ti-5553 alloy is assessed using a modulated laser powder bed fusion method. Cylindrical samples were printed with a wide range of volumetric energy density (VED). Density evaluation was practiced by the Archimedes method and X-ray computed tomography (XCT). Surface roughness analysis and hardness mapping were further used to characterize the as-built samples. In addition, the microstructure was studied using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. It was observed that low and high VED values resulted in an increase in the level of porosity. The highest relative density of 99.92% and surface roughness of

The fabrication friction stir welded lap joints with Al 7075-T6 sheets is examined with a wide range of tool pin geometries and dimensions while comparing microstructures, bonded area geometry, hardness, and fracture load during overlap shear testing. The tool pin geometry and features significantly affected the hook geometry and thus weld strength and failure mode. A hook feature is prone to forming when a larger diameter or helical threaded tool pins are used and is shown to deteriorate overlap shear fracture load by reducing the bonded ligament in the upper sheet. This hook feature can be controlled by removing the helical threads on the tool pin and replacing these with concentric grooves. The overlap shear fracture load is controlled by a combination of the sheet thickness, the width of the bonded area, and extent of the hook feature. These factors are captured in a model which was shown to provide good predictions of the fracture load and can be used to select tool pin sizes for varying overlapping sheet thicknesses.

This paper critically assesses the recent trends in aluminum-magnesium dissimilar welding and suggests a key design guideline to successfully improve the weld joint quality through addition of interlayer. First, the paper describes the main issue of incompatibility between these metals and considers the root cause of the problem, i.e., the Al-Mg-based intermetallic compounds (IMCs). It then reviews the recent trends of interlayer addition in various welding processes to mitigate Al-Mg IMCs. Focusing on laser welding, the paper finally proposes a 3-step design guideline in Al-Mg dissimilar welding through addition of an interlayer and presents a case study of using pure Ni foil as a proof of concept. The design guideline has shown to be an effective means to predict and prevent the formation of deleterious intermetallics.

This study evaluates the distribution of residual stress in friction stir weld (FSW) joints in AA7075 alloy using a semi-destructive technique (depth-controlled nanoindentation), and compares the results to a non-destructive method (neutron diffraction). The FSW process offers many benefits in AA7075 alloys such as grain refinement, prevention of solidification cracking, and reduced heat-affected zone softening. To examine the effects of welding parameters on the development of residual stress in FSW joints, different tool rotation speeds were applied on 8-mm-thick sheets of Al–Zn–Mg–Cu alloy. Nanoindentation and neutron diffraction measurements reveal variations in the residual stress within the nugget zone, thermos-mechanically affected zone, and heat-affected zone as compared to the base metal. The trend in residual stress values obtained from nanoindentation agrees with that from neutron diffraction measurements. The application of higher travel speed was found to reduce the residual stresses to negligible values, most likely as the result of an auto-stress relieving mechanism caused by higher temperatures and slower cooling rates.

A novel closed-loop process is demonstrated to control deposition microstructure during laser additive manufacturing (LAM) in real-time. An infrared imaging system is developed to monitor surface temperatures during the process as feedback signals. Cooling rates and melt pool temperatures are recorded in real-time to provide adequate information regarding thermal gradients, and thus control the deposition microstructure affected by cooling rates during LAM. Using correlations between the cooling rate, traveling speed, and the clad microstructure, a novel feedback PID controller is established to control the cooling rate. The controller is designed to maintain the cooling rate around a desired point by tuning the traveling speed. The performance of the controller is examined on several single-track and multi-track closed-loop claddings in order to achieve desired microstructures with specific properties. Results indicate that the closed-loop controller is capable of generating a consistent controlled microstructure during the LAM process in real-time.