One of the most important issues in three sheet resistance spot WELDing is the insufficient growth of the WELD NUGGET in the sheet/sheet interface, where it is most needed. This reduces the mechanical properties of the joint and increases the tendency to fail in the interfacial failure mode. In this paper the effect of sheet thickness on the pattern of WELD NUGGET development during resistance spot WELDing of three low carbon steel sheets of equal thickness is studied. Results showed that there is a critical sheet thickness at which the fusion zone size at the sheet/sheet interface is nearly equal to its size at the geometrical center of the joint. When sheet thickness is lower than the critical value, an elliptical NUGGET is formed in which the WELD NUGGET growth in the geometrical center of the joint is higher than the sheet/sheet interface. While, increasing the sheet thickness above the critical size causes the formation of a non-elliptical NUGGET in which the WELD NUGGET growth mostly occurs in the sheet/sheet interfaces.

Today, laser WELDing technology is one of the new methods in manufacturing. Laser spot WELDing is used to connect thin sheets of austenitic stainless steel in the manufacture of kitchenware. The strength and size of the WELD NUGGET are two important parameters in determining the quality of laser spot WELDing. In this study, thin sheets of stainless steel 316 with a thickness of 0. 7 mm were laser spot WELDed. To perform this WELDing, a medium power Nd: YAG laser WELDing machine was used and the effects of effective laser parameters on the strength and size of the WELD button were investigated experimentally. Laser frequency at three levels of 5, 7 and 9 Hz, peak laser power at three levels of 1670, 1750 and 1800 W and pulse ON time at three levels of 6, 8 and 10 milliseconds were selected as parameters and test levels. Taguchi L9 method was used to design the experiments. The experimental results show that with increasing laser power, the diameter of the WELDing button decreases, with increasing the pulse ON time, the diameter of the WELDing button first increases and then decreases, and with increasing laser frequency, the diameter of the WELDing button decreases and then increases. In addition, with increasing pulse ON time and laser frequency, the strength of WELD NUGGET increases, and with increasing laser power, the strength of WELD button increases firstly and then decreases.

In this paper, we show how Ferrite- martensite steel is produced by annealing operation, meanwhile tensile behavior of resistance spot WELD and the effects of the resistance spot WELDing parameter and tensile failure modes in this type of steel will be examined. Design experiments were done by Taguchi statistical method and because of the number of studied parameters and factors, we chose L8 array.Parameters which could be controlled in resistance spot WELDing include WELDing time, the electrical current through the electrodes and the pressure which here is considered as factors affecting the operation and tensile strength WELDed factor is examined as a test answer. In order to predict the optimal parameters of the resistance spot WELDing, signal to noise ratio is used in Taguchi statistical method.Generally, spot WELD failure occurs in two modes: interfacial and pullout. The results show that by increasing the diameter of the WELD NUGGET, pullout failure and the pullout with tear sheets becomes more likely to happen. Results of Taguchi statistical method also show that the impact of the electrical current parameter of the spot WELDing machine compared to other properties was higher and it is less effective with increasing current. As well as SEM images of WELD fracture, surfaces have been taken and the results indicate ductile fracture in pullout mode and cleavage in interfacial mode of fracture.

Friction Stir WELDing (FSW) is a solid state WELDing method. Now, for joining the variety of materials, especially dissimilar metals, has many applications. This method has no restrictions on the fusion WELDing. In addition to its many advantages, including the joining of metals with different melting points. In this paper, a successfully joint between Al5050Aluminum alloys to AISI304 stainless steel was reported. Friction Stir WELDing (FSW) process was used for joining these dissimilar materials. In friction stir WELDing many parameters such as tool rotational speed, feedrate, offset and pin profile were effective on microstructure and mechanical properties of WELD NUGGET by. This paper is focused on the effect of tool rotational speed, feedrate and offset on tensile strength and micro-hardness. In addition, effect of annealing operations was investigated on m crostructure and mechanical properties of the WELD NUGGET. The elongation and tensile strength of the WELD NUGGET were increased 100 and 9 percent respectively by the annealing process.

In this research, microstructure and mechanical performance of dissimilar resistance spot WELDed DP780/DP980 dual-phase steels were studied utilizing optical microscope, microhardness, and tensile shear tests. Resistance spot WELDing (RSW) was performed in the current range of 7 to 12 kA, with 0. 5 kA steps. At WELDing currents lower than 7 kA low amount of melting led to the very low strength of the joints due to small WELD NUGGET diameter. The results showed that an increase in WELDing current from 7 kA up to 11 kA, result in an increase in WELD NUGGET diameter. Further increase of WELDing current (higher than 11 kA), however decreased the WELD NUGGET diameter due to severe melt expulsion. Microstructural studies showed that WELD NUGGET was primarily comprised of martensite, and the heat-affected zone (HAZ) of both sides of the joint was comprised of three different microstructural zones; upper-critical HAZ (UCHAZ), inter-critical HAZ (ICHAZ), and sub-critical HAZ(SCHAZ). Microhardness test showed that at both sides, softening occurred at SCHAZ. The results of the tensile shear test showed that both peak load and fracture energy of the joints followed approximately the same trend as WELD diameter with WELDing current. Two different fracture modes of interfacial failure (IF) and pullout failure (PF) were observed in the tensile-shear test. At WELDing currents lower than 10 kA, the failure occurred in IF mode, while at higher WELDing currents, PF was dominant. WELD NUGGET diameter at WELDing current of 10 kA; i. e., critical WELD NUGGET diameter, was ~8. 5 mm.

In this study, the effects of process parameters including WELD current and electrode force on the microstructure of resistance spot WELDing on Zr-1%Nb alloy sheets of 0.3mm thickness were investigated. In the microhardness investigation of the WELD NUGGET cross section, the Vickers hardness measurement was performed in the direction of the WELD NUGGET diameter on a base metal, HAZ, and WELD NUGGET for the WELDed specimens with different parameters. Applying more electrode force in the same WELDing time yielded the grain growth which was found to be an important observation in this study. In the metallographic images, it was observed that the grains were deformed to be longer in the heat flow direction when more electrode force was applied. The hardness measurement of the WELD zones and base metal showed that, the WELD NUGGET had a maximum amount of hardness where it decreased in HAZ and subsequently in the base metal. This difference is due to transformation of the a+b and b phases. Transformation from b to a phase, which was carried out by a massive diffusion process and formation of the Widmanstatten a structure was achieved by slow cooling. The mentioned structure was found to be harder and stronger than the equiaxed a microstructure of the WELD metal.

This research looks at how microstructure and mechanical properties change in resistance spot WELDs of QP980 advanced high-strength steel. It specifically focuses on the effects of zinc coating and how it influences WELD NUGGET formation, mechanical properties, and fracture behavior. The study involved microscopic examinations, mechanical tests, and finite element simulations to determine the thermal history of different WELD zones. A key finding was that rapid cooling during the WELDing process led to the formation of, metastable phases, such as martensite, in both the WELD NUGGET and the heat-affected zone. A finite element model of the WELDing process was used to simulate heat distribution and analyze the microstructure in various WELD regions. This model showed that reaching the peak temperature during four-pulse resistance spot WELDing is delayed. This delay, along with proper hold times, helps prevent the formation of voids. The simulated thermal history and the rapid heating/cooling conditions effectively predicted the evolution and transformation of the microstructure in different WELD areas. It was found that the presence of a zinc coating, and the resulting reduction in electrical contact resistance, delayed the formation of the WELD NUGGET at lower WELDing currents. However, at higher currents, the primary source of heat generation shifted from contact resistance to bulk resistance within the steel sheet. This led to larger WELD NUGGETs in coated samples compared to uncoated ones. While uncoated samples showed higher WELD NUGGET hardness (512 Vickers) and greater tensile-shear strength (with a maximum load-bearing capacity of 28.1 kN in uncoated samples versus 24 kN in coated samples), coated samples were able to achieve the critical WELD NUGGET size for a change in fracture mode at lower WELDing currents (9 kA compared to 9.5 kA).

The purpose of this study is to investigate the effect of resistance spot WELDing (RSW) parameters on NUGGET size and ultimate strength of Magnesium alloy sheets AZ61 under tensile-shear test. In this study microstructural examination and hardness measurements were carried out on the WELDed samples. The results show that the WELD NUGGET zone is divided into two separate parts: the equiaxed dendritic zone (EDZ) perched at the center of the WELD NUGGET and the columnar dendritic zone (CDZ) situated around the fine-grained zone having it surrounded. The effect of the following three parameters: electric current, WELDing time and electrode force on the dimensions of the WELD NUGGET and the WELDed ultimate strength is investigated. The response surface method (RSM) is employed to examine the effects of WELDing parameters and to attain optimum parameters. The analysis of variance (ANOVA) results of RSM model shows that however the tensile-shear strength and NUGGET size are improved with increasing the WELDing current and WELDing time, the WELDing current is the most influential parameter. In addition, the optimal values for the WELDing parameters are calculated to achieve the maximum NUGGET size and the ultimate strength of WELDed joint. Finally, a regression model is proposed in order to predict the peak load and the NUGGET size as function of the mentioned WELDing parameters.

The main purpose of this study is optimization of resistance spot WELDing of AZ61 Mg alloy to achieve maximum NUGGET size and minimum tensile residual stresses in WELDing area. Since the stability and strength of a WELDed structure is strongly dependent on the NUGGET size and the residual stresses, an integrated artificial neural networks and genetic algorithm is utilized to optimize the WELDing parameters. In this study, the resistance spot WELDing process is simulated by a 2D fully coupled structural-electrical-thermal finite element model. The finite element model is developed to predict of the NUGGET size and the residual stresses in the WELDing area. In order to validate the FE model, the results are compared with the obtained results from the experimental tests. The results show that the FE model has a good agreement with the experimental tests. The input parameters for optimization are: electrical current, WELDing time and electrode force. The results show that the integrated optimization algorithm is successful in determining the optimized WELDing parameters. Based on the optimization results, the maximum NUGGET size 6. 33 mm and the minimum tensile residual stress 228 MPa are achievable by using 16kA, 16 Cycles and 848 N as current, WELDing time and electrode force respectively.