Identical Welding Parameters Research Articles

Morphological Characterization and Failure Analysis of the Ultrasonic Welded Single-Lap Joints.

Ultrasonic welding technology represents an advanced method for joining thermoplastic composites. However, there exists a scarcity of systematic investigations into welding parameters and their influence on the morphological characteristics and quality of the welded regions. Furthermore, a comprehensive experimental understanding of the welded joint failure mechanisms remains deficient. A robust model for simulating the failure behavior of welded joints under loading has yet to be formulated. In this study, ultrasonic welded specimens were fabricated using distinct welding control methods and varied parameter combinations. Diverse experimental methodologies are employed to assess the morphological features of the welded areas, ascertain specimen strength, and observe welding interface failure modes. Based on a cohesive model, a finite element model is developed to predict the strength of the ultrasonic welded joints and elucidate the failure mechanisms. The results showed that, under identical welding parameters, the specimens welded with a high amplitude and low welding force exhibit superior welding quality. The specimens produced under displacement control exhibit minimal dispersion in strength. The proposed finite element model effectively prognosticates both welded joint strength and failure modes.

High-Strength Ductility Joining of Multicomponent Alloy to 304 Stainless Steel Using Laser Welding Technique

In this work, a series of multicomponent alloys (CoCrFeNi, CoCrNi, and CoNiV) were laser welded with 304 stainless steel (304ss), and detailed comparisons on microstructural characteristics and mechanical properties were conducted for dissimilar laser welded joints. It is revealed that all of the dissimilar laser welded samples possessed defect-free joints and the corresponding fusion zone consisting of fcc single-phase showed homogeneous element distribution accompanied by a narrow element gradient in the vicinity of the fusion zone boundary. After laser welding with identical welding parameters, equiaxed grain was observed on the side of multicomponent alloy, while coarse columnar grain was obtained on the side of 304ss. Especially, the columnar grains of the fusion zone on the side of 304ss disclosed preferential <001> growth direction in the CoCrFeNi/304ss and CoCrNi/304ss welded joints. Furthermore, all of the dissimilar laser welded joints were fractured in the fusion zone, attributing to the drastic loss of strength in the fusion zone with coarsened grain. It is worth noting that a special lamellar structure that merged by dimples was found in the fracture surface of the CoNiV/304ss joint, closely related to the existence of the V-enriched region. Finally, a high strength-ductile synergy can be achieved by laser welding CoNiV alloy to 304ss, which showed a yield strength of 338 MPa, ultimate tensile strength of 686 MPa, and total elongation of 28.9%. These excellent mechanical properties prevailed in the potential of a CoNiV/304ss laser welded joint to be applied as a structural material.

A method for evaluation of weld overlays exposed to combined wear and very high cycle fatigue conditions

Key machinery components used for diminishing, transporting or processing massive volumes of material in heavy industries are severely exposed to combinations of different wear mechanisms, like abrasion and surface fatigue. The microstructure and wear properties of state of the art iron based welding alloys used as surface protection do not only depend on the nominal chemical composition of the welding consumables and their manufacturing route, but also on the base material, variations in process technology and applied welding parameters. Commonly used wear and hardness and test or microstructural investigations are either cost and time consuming or do not provide a complete understanding about the material behavior of surface coatings exposed to combined wear including fatigue. Thus the aim of this study was to prove the concept of using ultrasonic fatigue testing as new method to understand and predict the behavior of welded surface coatings in a fast and reproducible way. Two flux cored wires from different manufacturing lines, but of the same nominal chemical composition were compared applying identical welding parameters. As a result, the two wires could be distinguished clearly by applying the ultrasonic fatigue test method.

Selection of electrode tips for the resistance spot welding of dissimilar stainless steels

This research sought to resolve the issue of electrode tip selection used in the resistance spot welding for two different stainless steel grades under otherwise identical welding parameters: SUS316 and SUS425. The study used a full fractional design in order to perform the analysis of the variables involved, while the quality of the weld was assessed by considering the indentation depth, penetration, and nugget diameter. The results of the study described the nugget diameter and penetration for all welds with the various different electrode tips which met the specified requirements of the customers. A single type of upper R30 and lower R30 electrodes achieved acceptable indentation depth. Ideally, good weld quality would demand a large nugget diameter, shallow indentation, and good penetration, all contribution to an acceptable overall appearance. Both R30 electrode tips are able to achieve the desired quality requirements in the spot welding process.

Effects of tool design on the microstructure and mechanical properties of refill friction stir spot welding of dissimilar Al alloys

Al6022-T4/Al7075-T6 welds were fabricated by refill friction stir spot welding using different tool designs with identical welding parameters. Cracks and voids were formed in the welds manufactured using a standard tool. When tool penetration depth is low, metallurgical bonding was not formed completely through the weld center despite the presence of mechanical inter-locking. When tool penetration was increased to 1.5mm, more intermixing and metallurgical bonding was formed in the weld center with some voids at the weld boundary. Defect-free welds were fabricated using a modified tool with three grooves or notches in the tool sleeve, which improved metallurgy bonding, material intermixing and mechanical inter-locking at the weld interface. The intermixed structure resulted from incorporation of the top and bottom sheet materials promoted by the grooves on the bottom of the tool sleeve, and this suppressed formation of cracks. Thus, the welds exhibit higher overlap shear strength with less sensitivity to welding parameters.

Static and fatigue performance of weld bonded dual phase steel sheets

Lap joints of dual phase steel sheets of 1·0 mm were prepared by adhesive bonding, spot welding and weld bonding processes using a one component epoxy base structural adhesive. Mechanical properties of the joints were evaluated by tensile shear and fatigue tests. The size of the weld nugget for both spot weld and weld bond was measured for different welding parameters (current, time) and compared. For identical welding parameters, weld bonded nuggets exhibit higher nugget diameter. Tensile shear strength of weld bonded joints is 40 and 58% higher than spot welded joints and 15 and 39% higher than adhesive bonded joints and for DP590 and DP780 steels respectively. Considering 106 cycles, the endurance limit of weld bonded joint is much higher than spot welded joint but smaller than adhesive bonded joints. Overall the performance of weld bonded joints is superior to those of resistance spot welding.

Influence of filler material on micro- and macro-mechanical behaviour of laser-beam-welded T-joint for aerospace applications

3.2mm thick laminated skins of AA7475 alloy and 2.5mm thick extruded stringers of the alloy PA765 were T-jointed by laser beam welding. Two different joints were fabricated using identical welding parameters but two different alloys as welding wires, AA5356 and AA4047. The microstructure, the tensile, and the failure behaviours of the two welded joints are studied by means of optical and electronic microscope, micro-indentation, and tensile testing. Weld beads extension using AA5356 are larger than those using AA4047. Microstructure of the welded joints is quite similar: at the centre of the fusion zone, cellular dendrites are present; near the fusion line in the fusion region, a chill zone and parallel dendrite arms are found; and an evident heat-affected zone is observed between the fusion line and the parent material. Microhardness tests reveal that the partially melted zone is a weak band in the welded specimens. Indeed, for both joints, failure took place at the partially melted zone upon tensile loading. Hoop testing demonstrates that AA4047 joints present a lower yield stress than AA5356 joints although both joints show similar tensile strength and elongation at break. AA4047 joints show more strength than AA5356 joints upon T-pull testing.

Effect of initial base metal temper on mechanical properties in AA7050 friction stir welds

The effect of initial base metal temper on mechanical properties in AA7050 friction stir welds was investigated. AA7050 plates, 6·4 mm thick, with three different heat treatment conditions (T7451, T62 and W), were friction stir welded using nearly identical welding parameters, followed by post-weld aging approximating a T7451 heat treatment. The microstructure, transverse hardness profiles and transverse tensile properties were characterised for these three welds. Experimental results show that preweld heat treatment conditions of AA7050 base metal have significant effect on the mechanical properties of the friction stir welds. Friction stir welding of AA7050 in the W condition, followed by post-weld aging, can change the fracture location from HAZ to weld nugget and increase tensile and yield strengths and elongation in transverse tension, relative to welding in T62 or T7451 conditions.

Effects of Nb on the microstructure and corrosive property in the Alloy 690–SUS 304L weldment

A study of the microstructure and corrosion of dissimilar weldments of Alloy 690 and SUS 304L with various additions of niobium (Nb) (0.1, 1.03, 2.49, and 3.35% by weight) in the flux of coated electrodes is presented. With identical welding parameters and procedures, the weldments were butt-welded in three layers by shielding metal arc welding (SMAW), with each layer being deposited in a single pass. The results show that the dendritic microstructure in the fusion zone changed from a cellular to columnar dendrite and equiaxed dendrite with increasing Nb addition. Furthermore, the interdendritic phase increased in volume and changed in composition from an Al–Ti oxide to a mixture of Nb–Si phase and Nb-rich phase. Nevertheless, it was clearly observed that Cr 7C 3 precipitated at the grain boundaries of the low Nb weldment root pass. Finally, the results revealed that corrosion occurs primarily at the grain boundaries and within the interdendritic regions of the weldements irrespective of the level of Nb addition. For the region of abundant formation of Nb-rich phase, the high-Nb weldment had a relatively low corrosion resistance.

Variation in diffusible Hydrogen Content and Hydrogen Assisted Cracking Susceptibility of Cr-Mo Steels

In this paper results obtained from diffusible hydrogen (HJ measurement and hydrogen assisted cracking susceptibility (HAC) of three different Cr-Mo steel welds are discussed. H 0 measurements were carried out using a gas chromatograph and HAC susceptibility studies using the ur-modified hydrogen sensitivity test (UT-Modified HST). Specimens for both these studies were prepared by employing identical welding parameters. Results showed that with increase in alloy content the cracking susceptibility of the steel increased while H 0 content in the weld decreased. The decrease in the H 0 content is explained based on decrease in the apparent diffusivity and increase in the apparent solubility of hydrogen with alloy content. These are in turn attributed to increase in the density of hydrogen traps with alloy content. Regression analysis of the results showed that it is possible to predict the safe preheat temperature for the steel from the composition if H 0 content in the weld is known.