This paper investigated various aspects of replacing existing micro-resistance spot welding (micro-RSW) with micro-laser spot welding for joining Inconel 718 thin foils to thick 410 steel stack-up to ...allow faster, non-contact joining together with flexibility in spot positioning and removal of tip dressing required for RSW electrodes. The joint quality was evaluated based on the mechanical strength, microstructural characteristics and joint strength at elevated temperature as these joints are often used for high-temperature applications. Experimental investigations were performed using micro-RSW and micro-laser spot welding to obtain the 90° peel and lap shear specimens, each comprising four spots. The obtained strength from laser joints was significantly higher than that of micro-RSW joints due to larger weld nugget formation and interface width. The process map for obtaining good quality welds was also identified, and about a 17% reduction in joint strength was obtained when welded specimens were subjected to elevated temperature (i.e., 500 °C) in comparison with room temperature. This reduction was compensated for using the flexibility of laser welding to add two extra spots. The overall performance of the micro-laser spot welds was found to be better than the micro-RSW considering joint strength, flexibility in placing the spots and time to produce the welds.
This study aims to find the best conditions of resistance spot welding in commercial Aluminium AA1050 to obtain the maximum tensile shear strength of the joint using a low-power supply welding ...machine. The chosen parameters for this study were welding current, welding time, and electrode force using a 90 kVA welding machine. The investigation used the DoE method with Taguchi’s technique to reduce the number of experiments where two sheet thicknesses (1 mm and 2 mm) were used in this work. The software program Minitab 18 analyzed the results using the main effects plots and the interaction plots to identify the most significant parameters and their effect on the joint strength. The best conditions for maximum tensile shear force were 14.85 kA welding current and 0.79 kN electrode force for both thicknesses and two cycles and 12 cycles welding time for 1 mm and 2 mm sheet thickness, respectively. The maximum tensile strength obtained was 250 N and 225 N for 1mm and 2mm sheet thickness, respectively. A mathematical equation was developed to predict the shear force with 19.9 % and 17.9 % error for 1 mm and 2 mm thicknesses, respectively. The best conditions were applied in ANSYS 2022R1 multi-physics to obtain the temperature distribution with time history, where the result shows the nugget size according to the molten temperature. The percentage of discrepancy between actual and numerical nugget size was 8 %.
HSLA steels are widely preferred in the automotive industry due to their advantages of high strength, lightening of vehicle weight and formability. The fact that a lot of welding processes are ...carried out during the creation of the vehicle body has made the welding operations of these steels an important topic. In this study, zinc coated HX340LAD+Z sheet material was welded by RSW application in factory conditions. The welding opera-tion was carried out with different current intensities and 300 spot welds for three different electrodes, keeping the weld duration constant. After the welding trials, the shortening of the electrodes was examined and information about the electrode lifetime was obtained. The weld core diameter was measured on the sheet metal also microstructure and micro-hardness investigations were made. As a result of the findings, information was obtained about weld hardness and collapse. Determination of splashing in the HX340LAD+Z ma-terial was provided by SEM imaging and EDX studies. It was determined that F type Copper electrode was more efficient.
Abstract
A6061-T6 aluminum alloy and DP590 duplex steel with a galvanized layer for resistance spot welding, the investigation of welding current on the A6061-T6 aluminum alloy / DP590 steel joint ...interface intermetallic compound and the effect of shear resistance. The results found that when the welding current increased, the intermetallic compound layer first became thicker and thinner, while the joint shear force always increased, and when the welding current reached 13 kA, the shear force was 4.0 kN.
Press-hardened steels (PHS) are widely used in the safety cage of vehicle body-in-white structures owing to their high strength which is attained from phase transformation during hot stamping. ...Resistance spot welding of PHS produces a martensitic microstructure in the fusion zone (FZ) exhibiting brittle failures with low energy absorption capacity in the case of a vehicle crash event. Typically, the martensitic microstructure impairs the toughness of the fusion zone leading to interfacial failure (IF) which is perceived to be undesirable for crashworthiness. Tempering of the martensite in the FZ has been adopted as a means to improve weld toughness; however, differential tempering was observed across the nugget diameter in this study. The differential tempering was attributed to the presence of pre-existing irregular voids formed during the welding cycle which altered the current flow at the weld center and periphery. Findings revealed that reducing the voids in the nugget leads to effective tempering and improved mechanical properties of the joint when performed under the right temperature and time regime. The optimal tempering condition showed an improved cross tension peak load of 36% and 33% in the energy absorption capacity. The improved cross-tension performance was attributed to the tempered martensitic structure in the FZ which promoted crack deflection leading to a pull-out failure mode.
•Steel and aluminium alloy were resistance spot welded with interlayer successfully.•Welded joint of steel and aluminium alloy with 4047 interlayer was a brazed joint.•Fe2(Al,Si)5 and Fe4(Al,Si)13 ...were formed at the steel/aluminium interface.•Reaction diffusion at the interface was inhibited by introduction of silicon atoms.•Welded joint property was improved greatly with the interlayer thickness of 300μm.
Dissimilar materials of H220YD galvanised high strength steel and 6008-T66 aluminium alloy were welded by means of median frequency direct current resistance spot welding with employment of 4047 AlSi12 interlayer. Effects of interlayer thickness on microstructure and mechanical property of the welded joints were studied. The welded joint with interlayer employed could be recognised as a brazed joint. The nugget diameter had a decreased tendency with increasing thickness of interlayer under optimised welding parameters. An intermetallic compound layer composed of Fe2(Al,Si)5 and Fe4(Al,Si)13 was formed at the interfacial zone in the welded joint, the thickness and morphology of which varying with the increase of interlayer thickness. Reaction diffusion at the steel/aluminium interface was inhibited by introduction of silicon atoms, which restricted growth of Fe2(Al,Si)5. Tensile shear load of welded joints experienced an increased tendency with increasing interlayer thickness from 100 to 300μm, and the maximum tensile shear load of 6.2kN was obtained with interlayer thickness of 300μm, the fractured welded joint of which exhibiting a nugget pullout failure mode.
The weldment consisted of four zones: fusion zone, partially melted zone, heat affected zone and base metal. Liquation film, liquated grain boundaries, liquation crack and softening zone were ...observed in the partially melted zone. Compared to single pulse resistance spot welding (RSW), the double pulse welding with a higher secondary current led to an enhancement in tensile-shear strength and a desirable failure mode, while a medium level value improved cross-tensile strength and ductility ratio. The partially melted zone acted as a crack sensitive area due to P segregation, causing a distinct partial thickness-partial pullout failure in the tensile-shear tests and pullout interfacial failure in the cross-tensile tests. Liquation crack, referred as a secondary crack initiation, further promoted crack propagation in these failures. The partial thickness-partial pullout failure can be divided into three stages: crack initiation, crack propagation and instantaneous fracture. The fracture mechanism were quasi-cleavage fracture during crack propagation. Then, the instantaneous fracture is occurred with ductile characteristic.
The widespread adoption of ultra-high strength steels, due to their high bulk resistivity, intensifies expulsion issues in resistance spot welding (RSW), deteriorating both the spot weld and surface ...quality. This study presents a novel approach to prevent expulsion by employing a preheating current. Through characteristic analysis of joint formation under critical welding current, the importance of plastic material encapsulation around the weld nugget (plastic shell) at high temperatures in preventing expulsion is highlighted. To evaluate the effect of preheating on the plastic shell and understand its mechanism in expulsion prevention, a two-dimensional welding simulation model for dissimilar ultra-high strength steel joints was established. The results showed that optimal preheating enhances the thickness of the plastic shell, improving its ability to encapsulate the weld nugget during the primary welding phase, thereby diminishing expulsion risks. Experimental validation confirmed that by employing the optimal preheating current, the maximum nugget diameter was enhanced to 9.42 mm, marking an increase of 13.4 % and extending the weldable current range by 27.5 %. Under quasi-static cross-tensile loading, joints with preheating demonstrated a 7.9 % enhancement in maximum load-bearing capacity compared to joints without preheating, showing a reproducible and complete pull-out failure mode within the heat-affected zone. This study offers a prevention method based on underlying mechanisms, providing a new perspective for future research on welding parameter optimization with the aim of expulsion prevention.
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A multi-process joining technique that combined resistance spot welding and friction element welding was used to produce a three-sheet multi-stack of advanced high strength steel and ...precipitation hardened aluminum. Each weld process was tested independently and as a combination to better understand how multi-step welding affects joint performance. Weld interfaces and surrounding heat affected zones were investigated using microstructural and mechanical techniques, including scanning electron microscopy and nanoindentation. All tests indicated that excellent strength was maintained above the maximum breaking force threshold regardless of offset distance between the friction element weld and the center of the resistance spot weld nugget. A change in fracture mode was observed with interfacial fracture occurring at offset distances below 7 mm and nugget pull out or partial thickness failure occurred at offset distances above 7 mm. The present study indicates that hybrid joining techniques have minimal effect on both the mechanical and microstructural weld properties and allow for new dissimilar metal weld designs to be implemented in the automotive industry.
Advanced high strength steels (AHSS) used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal ...embrittlement (LME) during welding. Recent studies have examined the impact of the welding electrode geometry on LME cracking severity and found there to be some effect, but did not explore the responsible mechanisms for the changes. This work shows that a radius tip electrode provides minimal cracking while a truncated cone shape showed severe LME, particularly in the shoulder region. Thermo-mechanical simulations showed the significance of the thermal contact at the outer region of the electrode/sheet interface (weld shoulder). It was observed that when the water-cooled electrode presses into the steel during the welding, causing a contact between the steel surface and the electrode sidewall, a sudden local cooling of the weld shoulder occurs. This cooling causes contraction and tensile stresses on the material surface, leading to LME. Additionally, the magnitude and location of heat transfer between the steel and electrode is controlled by the thermal contact conductance.
