Search Results (22)

The microstructure and mechanical properties of welded joints of API 5L X-52 steel plates cladded with AISI 316L-Si austenitic stainless steel were evaluated. The gas metal arc welding process with pulsed arc (GMAW-P) and controlled arc oscillation were used to join the bimetallic plates. After the root welding pass, buttering with an ERNiCrMo-3 filler wire was performed and multi-pass welding followed using an ER70S-6 electrode. The results obtained by optical and scanning electron microscopy indicated that the shielding atmosphere, welding parameters, and electric arc oscillation enabled good arc stability and proper molten metal transfer from the filler wire to the sidewalls of the joint during welding. Vickers microhardness (HV) and tensile tests were performed for correlating microstructural and mechanical properties. The mixture of ERNiCrMo-3 and ER70S-6 filler materials presented fine interlocked grains with a honeycomb network shape of the Ni–Fe mixture with Ni-rich grain boundaries and a cellular-dendritic and equiaxed solidification. Variation of microhardness at the weld metal (WM) in the middle zone of the bimetallic welded joints (BWJ) is associated with the manipulation of the welding parameters, promoting precipitation of carbides in the austenitic matrix and formation of martensite during solidification of the weld pool and cooling of the WM. The BWJ exhibited a mechanical strength of 380 and 520 MPa for the yield stress and ultimate tensile strength, respectively. These values are close to those of the as-received API 5L X-52 steel. Full article

This study investigated the control of porosity during gas metal arc welding with pulsed arc (GMAW-P) of complex-phase 780 (CP780) galvanized steel. Due to the Zn coating on this type of steel, porosity forms during welding as a result of Zn vaporization. The objective was to optimize the welding parameters to minimize porosity with a design of experiments using an L9 orthogonal array to analyze the effects of peak current (I_p), pulse time (t_p), and pulse frequency (f) in high-speed welding conditions. The results showed that porosity was significantly reduced with a peak current of 313 A, a frequency of 10 Hz, and a pulse time of 10 ms, achieving ~0% porosity in the validation welding trials. A microstructural analysis identified allotriomorphic ferrite, Widmanstätten ferrite, acicular ferrite, bainite, and martensite in the heat-affected zone (HAZ). A predictive model to anticipate the percentage of porosity with an R² of 99.97% was developed, and an ANOVA determined the peak current as the most critical factor in porosity formation. Full article

In this study, the theoretical welding parameters influencing porosity formation were examined with the aim of reducing or minimizing porosity levels. An experimental design was implemented using the Taguchi methodology for data analysis, resulting in an L9 orthogonal array matrix of experiments. The welding variables considered in the orthogonal array were peak current, peak time, and frequency. Nine lap welds were performed on CP780 steel using the gas metal arc welding process with pulsed arc (GMAW-P), employing an ER70S-3 electrode as filler metal. The percentage of porosity was determined as a response variable, and the actual heat input was treated as a covariable, thereby identifying the welding parameters with the predicted values. Three repetitions were conducted with the optimal welding parameters to validate the Taguchi prediction. The quality of the welds was assessed through radiographic inspection, and metallographic preparation was performed, revealing the microstructure with 5% Nital for 12 s. The samples were analyzed using an optical microscope, and images were obtained with the collage technique. The results showed that the welding parameters predicted by the Taguchi statistics were favorable for all three predicted welded joints. The maximum percentage of porosity obtained was 19%, which was reduced to 1% using the Taguchi methodology, demonstrating the effectiveness of this statistical tool for process optimization. It was observed that for heat input values of 230 to 250 J/mm, the presence of porosities is dramatically reduced, finding a very small window that allows the gases generated by the burning of zinc to be expelled to the surface. Full article

The use of the orthogonal array L₄ allows a determination of the effect between the welding parameters peak current (I_p), background current (I_b) and frequency (f) on the porosities in a dissimilar welded lap joint of CP800 and XPF1000 steel weldment by the gas metal arc welding process with the transfer pulsed mode. According to the results, modifications in the welding parameters affect the heat input during welding. A heat input higher than 0.30 KJ/mm generates up to 0.32% porosity in the weld metal, while a heat input lower than 0.25 KJ/mm generates up to 28% porosity in the weld metal. The variation in heat input generated by the process allowed the observation of the final microstructure of the welded joints and the effect of mechanical properties such as hardness because the results show values of hardness from 300 Hv to 400 Hv in the heat affected zone (HAZ). Full article

In the welding process of thick plate narrow gap pulse gas metal arc welding (P-GMAW) overhead welding station, the arc characteristics and droplet transfer behavior that become more complex due to the combined effects of narrow gap groove, gravity, and welding torch oscillation. The welding stability is more difficult to control. High-speed imaging and electrical signal acquisition systems were established to observe and record the arc behavior and droplet transfer during the welding process at different oscillation widths, further revealing the formation mechanism of welding seam in narrow gap P-GMAW overhead welding station. Research has found that with an increased oscillation width, the arc deflects towards the sidewall from a trumpet-shaped symmetrically distributed around the center of the groove at an increasing deflection angle, and the droplet transfer changes from one droplet per pulse to multiple droplets per pulse, resulting in defects such as lack of sidewall fusion and undercutting of the weld seam. Based on the welding process discussed in this study, it is recommended to use an oscillation width of 2.6 mm. Full article

In fields, such as oil and gas pipelines and nuclear power, narrow-gap welding has often been used for the connection of thick and medium-thick plates. During the welding process, a lack of fusion was prone to occur due to groove size limitations, seriously affecting the service safety of large structures. The vertical oscillation arc pulsed gas metal arc welding (P-GMAW) method was adopted for narrow-gap welding in this study. The influence of the oscillation width on arc morphology, droplet transfer behavior and weld formation during narrow-gap welding was studied. Oscillation widths from 0 to 4 mm were used to weld narrow-gap grooves with a bottom width of 6 mm. The results show that, in non-oscillation arc welding, the arc always presented a bell cover shape, and the droplet transfer was in the form of one droplet per pulse, while the sidewall penetration of the weld was relatively small, making it prone to a lack of fusion. With an increase in the oscillation width, the arc gradually shifted to the sidewall. The droplet transfer mode was a mixed transfer of large and small droplets, and the sidewall penetration continued to increase, which was conducive to the fusion of the sidewall. However, when the oscillation width was wider than 3 mm, it led to the phenomenon of the arc climbing to the sidewall, and the weld was prone to porosity, undercutting and other welding defects. The oscillation width has a major impact on the stability of the welding process in vertical oscillation arc narrow-gap welding. Full article

Quench and tempered (Q&T) steels are widely used for a diverse range of applications, particularly in the mining and defence industry, where wear and unconventional loading are common. Furthermore, they are particularly prone to hydrogen assisted cold cracking (HACC), imposing a more careful selection of consumables and requiring a comparably higher welder skill level to fabricate defect-free structures. Therefore, the cost of fabrication of welded structures is higher when the more preferred welding technique of shielded metal arc welding, SMAW, is employed. The introduction of the modified pulsed arc mode of depositions, a variation to pulsed arc deposition, has improved the productivity rates and can be utilised by welders with a greater skill variations. In this study, full-strength butt welds of Q&T steel (AS/NZS 3597 Grade 700), with the thickness of 20 mm, are fabricated under a high level of restraint using both conventional SMAW and modified pulse gas metal welding (GMAW-P). The study investigated the economic feasibility of the two deposition modes and the propensity to cracking for the welded joints under high restraint conditions. Utilising the modified GMAW-P resulted in 63% and 88% reduction in the ‘Arc-On’ time and the total normalised fabrication time, respectively. However, strict controls must be implemented, due to the increased propensity to lack of fusion-type defects, to optimise the welding procedure and mediate for such defects if GMAW-P is to provide a techno-economically beneficial alternative to conventional SMAW when welding Q&T steels. Full article

A novel plasma-pulsed GMAW hybrid welding (plasma-GMAW-P) process is proposed for joining 6061 aluminum and zinc-coated steel. The results show that the change in welding heat input has little effect on the microstructure of the joint and the composition of the intermetallic compounds (IMCs) but only changes the thickness of the reaction layer (increased from 5 μm to 12 μm). when the plasma arc current is 20 A and the MIG current is 80 A, the welded joint obtained has the highest tensile-shear force. With the optimal process parameters, the weld strength obtained by filling ER4043 welding wire is the highest, accounting for 65% of the tensile-shear force of the base material. The effect of the plasma arc acting on the joint properties is studied through the microstructure and a tensile-shearing test. The action position of the plasma arc plays a significant role in the Al/steel interface, which directly influences the strength of the welded joints. Regardless of the plasma-GMAW-P style used to obtain the joints, Fe-Al IMCs appear at the interface. When the plasma arc is in front of the welding direction and the GMAW-P arc is in the rear, the tensile-shear force reaches the maximum of 3322 N. Full article

The processes of metal additive manufacturing (AM) are no longer confined to rapid prototyping applications and are seeing increasing use in many fields for the production of tools and finished products. The ability to design parts with practically zero waste, high precision, complex geometry, and on-demand fabrication are among the advantages of this manufacturing approach. One of the drawbacks of this technique is the productivity rate, as the parts are made layer by layer, which also increases the production cost. Moreover, even the working space is limited, especially for the powder bed fusion technique. In view of these disadvantages and in order to guarantee the profitability of this process, it should be oriented to the production of complex components that have a limited volume with a design adapted to additive manufacturing. One solution with which to circumvent these drawbacks is to combine the 3D printing process with conventional manufacturing processes. When designing products, one may choose to use additive manufacturing to create locally complex parts and assemble them with parts produced by conventional processes. On the other hand, and due to the limited AM printing chamber space, it may be necessary to print large parts in multiple smaller parts and then assemble them. In order to investigate the weldability of stainless steel 316L parts produced by laser powder bed fusion (L-PBF), the mechanical behavior of different welding assemblies is tested. Five configurations are studied: non-welded AM specimens, two AM parts welded together, one AM part and one laser cut part welded together, two laser-cut parts welded together, and non-welded laser cut specimens. Welding is performed using the Pulsed Gas Metal Arc Welding process (GMAW-P). Specimen strength is assessed through static and fatigue tests. The results demonstrate that 316L AM parts are weldable, and the tensile and fatigue properties of L-PBF 316L welded components and welded laser cut components are comparable. GMAW-P welding led to lower fatigue results for AM components than for other configurations, but the difference is not important. It was observed that welding defects may have a direct impact on mechanical properties. Full article

The heating and impact of arc and droplet acting on the weld pool lead to the transfer of mass, heat, and momentum, which affects the dynamic behavior of the weld pool and the microstructure in the P-GMAW process. In this paper, an image processing program is used to extract the dynamic behavior characteristics of the droplet transition and the weld pool in high-speed photography. The influence of the current waveform on the arc pressure and the impact of the droplet is quantitatively analyzed with different parameters. The dynamic behavior of the weld pool and the microstructure under different current waveform conditions are further studied. The internal relation of current waveform parameters to weld pool behavior and weld microstructure was expounded. The results show that the droplet impact is positively correlated with the pulse peak current. The rectangular wave pulse has a more significant droplet impact than the exponential wave with the same waveform parameters. The impact of droplet transition on the weld pool enhances the convective intensity of the weld pool. It slows down the cooling rate of the solidified weld microstructure below the tail of the weld pool, increasing the grain size of the weld microstructure. Full article

Quenched and tempered (Q & T) steels have numerous applications, particularly in the defence industry with welding as the main fabrication route. Since welding imparts stresses due to thermal gradients development during welding, plus the fact that the Q & T fabricated structures are expected to function in a complex loading environment, it is critically important to relax the welding stresses before exposing the parts to service conditions. The present study reports on the generated residual stresses when Bisalloy 80 is welded by pulsed gas metal arc welding (GMAW-P) and verifies the effects of post-weld heat treatment (PWHT) on the microstructural changes, removal or reduction of residual stresses and the resulting mechanical properties of the welded Q & T steel joints. Neutron diffraction was utilized to measure the residual stresses in the as-welded and after PWHT of the Bisalloy 80 steel weldments. High levels of tensile residual stresses reaching to the yield strength of the weld metal were present (642 ± 24 MPa) in the as-welded joints but were substantially reduced after PWHT (145 MPa ± 21 MPa, which is ~23% of the yield strength of the weld metal). PWHT led to microstructural changes in different regions of the parent and weld metals, including the formation of coarsened polygonal ferrite grains and bainitic ferrite laths. This finding is in line with hardness measurements, where hardness reductions were evident in the heat-affected zone (HAZ) and the weld metal (WM) of the heat-treated specimens. Full article

In this paper, the analysis of electrochemical corrosion performance and mechanical strength of weld joints of aluminum 6061 in two-heat treatment conditions was performed. The joints were produced by gas metal arc welding in pulsed mode. The original material exhibited precipitates of $\beta$ and $\beta$” phases in a volume fraction (Vf) of 2.35%. When it was subjected to a solubilization process, these phases were present in a Vf = 2.97%. This increase is due to their change in shape and distribution in clusters within the aluminum matrix. After the welding process, the best sample in the solubilization condition reached 117 MPa, while the original material achieved 104 MPa, but all samples showed a fracture in the fusion zone. This is attributed to the heat input that produces high and low hardness zones along the heat-affected zone and the welding zone, respectively. Moreover, the change in microstructure and phase composition creates a galvanic couple, susceptible to electrochemical corrosion, which is more evident in the heat-affected zone than in the other weld regions, exhibiting uniform and localized corrosion, as was evident by electrochemical impedance spectroscopy. The heat from the welding process negatively affects the corrosion resistance, mainly in the heat-affected zone. Full article

Alcohol withdrawal syndrome (AWS) represents an adverse consequence of chronic alcohol use that may lead to serious complications. Therefore, AWS requires timely attention based on its early recognition, where easy-to-apply diagnostic tools are desirable. Our aim was to characterize the performance of a short-scale AST (Anxiety, Sweats, Tremors) in patients from public general hospitals. We conducted a cross-sectional study of patients attended at the Emergency Department diagnosed with AWS. Three scales were applied: CIWA-Ar (Clinical Institute Retirement Assessment Scale-Revised), GMAWS (Glasgow Modified Alcohol Withdrawal Syndrome) and AST. Cronbach’s alpha and Cohen’s kappa tests were used for reliability and concordance. Factorial analysis and diagnostic performance including ROC curve were carried out. Sixty-eight males with a mean age of 41.2 years old, with high school education and robust alcohol consumption, were included. Mean scores for CIWA-Ar, GMWAS and AST were 17.4 ± 11.2, 3.9 ± 2.3 and 3.8 ± 2.6, respectively, without significant differences. The AST scale showed an acceptable reliability and concordance (0.852 and 0.439; p < 0.0001) compared with CIWA-Ar and GMAWS. AST component analysis evidenced tremor (77.5% variance), sweat (12.1% variance) and anxiety (10.4% variance). Diagnostic performance of the AST scale was similar to the GMAWS scale, evidencing a sensitivity of 84%, specificity of 83.3% and Area Under the Curve (AUC) of 0.837 to discriminate severe AWS, according to CIWA-Ar. The performance of the AST scale to evaluate AWS is comparable with the commonly used CIWA-Ar and GMAWS scales. AST further represents an easy-to-apply instrument. Full article

In this paper, a double pulse gas metal arc welding (DP-GMAW) for an AA6061-T6 aluminum alloy based on fewer basic welding parameters than the traditional DP-GMAW is proposed. This study compared the difference in pulse base currents ($\mathsf{\Delta }{I}_{\mathrm{b}}$) and the difference in the pulse peak currents ($\mathsf{\Delta }{I}_{\mathrm{p}}$) by analyzing the electrical signal and morphology properties of welded samples. The results indicated that changing $\mathsf{\Delta }{I}_{\mathrm{p}}$ caused welding defects or even welding failure easily. The welding stability after changing $\mathsf{\Delta }{I}_{\mathrm{b}}$ was much better than that after changing $\mathsf{\Delta }{I}_{\mathrm{p}}$. The individual fish-scale width of the weld joint remained unchanged when $\mathsf{\Delta }{I}_{\mathrm{b}}$ was at different values. In addition, the average absorbed work, tensile strength, yield strength and elongation of the weld joints obtained by different $\mathsf{\Delta }{I}_{\mathrm{b}}$ values reached 31.1%, 60.2%, 52.9% and 37.9% of the base metal, respectively. Full article

Joints of complex phase 780 (CP-780) advanced high strength steel (AHSS) were carried out by using an ER-CuAl-A2 filler metal for the gas metal arc welding pulsed brazing (GMAW-P- brazing) process and the ER-80S-D2 for the GMAW-P process employing two levels of heat input. The phases in the weld bead and HAZ were analyzed, and the evaporation of zinc by means of scanning electron microscopy (SEM) was also monitored. The mechanical properties of the welded joints were evaluated by tension, microhardness and vertical impact tests. It was found that there was greater surface Zn evaporation in the joints welded with the GMAW-P process as compared to the GMAW-P-brazing process. The best results in tensile strength were observed in the joints welded with GMAW-P-brazing process, which increased by ~68% with respect to those of the GMAW-P. This behavior can be attributed to the formation of an intermetallic complex compound Cu-Al-Fe in the fusion line. Full article