•This paper shows the current situation in two aspects in resistance spot welding.•The effect of process analysis is limited because methods lack physical support.•The quality control should combine ...quality estimation and energy delivery strategy.•Future works about the resistance spot welding are also provided.
Resistance spot welding (RSW) is frequently employed in current industrial occasions. However, the process is multi-field coupled and highly nonlinear, and full of uncertainties and disturbances. This paper presents recent primary advances and progress in process analysis and quality control of the RSW operations. Online welding process analysis, and relative online quality estimation for the welding products, are very important because they can help to save energy and improve the efficiency during actual production. It should deeply interpret the process characteristics, and then reasonable relations between selected monitoring process variables, such as dynamic resistance or electrode displacement, and quality criteria, such as nugget size or tensile-shear strength, can be established. Apart from online process analysis using mathematical tools, using different kinds of auxiliary measuring signals from external sensors and intrinsic process variables to monitor the process and obtain the quality information of the weld is presented and discussed. Then various process control works are reviewed. Besides the various parameters optimization methods, kinds of controllers, including feedback controllers, intelligent controllers and comprehensive controllers which combined the online quality estimation and control strategy application together, for obtaining welds with satisfactory quality, are respectively discussed. It can be seen that the establishment of general models to online process analysis, quality estimation and real time control system design for obtaining welds with satisfactory quality still remains a big challenge in reality. This work can provide references and enlightens for current academic researches or actual production in RSW relative area.
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•Dissimilar joints of aluminum to steel exhibited high static and fatigue properties.•A method was developed to compare fatigue properties of various dissimilar joints.•Static ...fracture energy was promising to predict the dissimilar joint fatigue property.•Stress intensity factors were used to explain the transition in fatigue failure mode.•High cycle fatigue was not strongly affected by brittle Fe-Al intermetallic layer.
Lightweight structures made of aluminum alloys and high strength steels are increasingly used for improving vehicle fuel efficiency. One barrier for joining aluminum and steel is the formation of brittle Fe-Al intermetallics that can have deleterious effects on joint ductility and strength under static loading conditions. However, it is unclear how the intermetallics affect the joint fatigue properties. In this study, the effect of intermetallics on fatigue properties of dissimilar metal joints between a 6xxx aluminum alloy and a high-strength steel is investigated on welds created by ultrasonic interlayered resistance spot welding (Ulti-RSW). Joint efficiency calculations are used to normalize the peak load so the fatigue properties of Ulti-RSW are compared with a wide range of joining processes in the literature. During fatigue testing the failure mode transitions from interfacial or button pull-out failure during low cycle fatigue loading (below 100,000 cycles) to through-thickness failure during high cycle (above 100,000 cycles). Based on the stress intensity factors calculated using a simple 2D fracture mechanics model, the transition in failure mode is attributed to the plastic deformation near the notch tip. Overall, this study shows that the intermetallics have little effect on the high-cycle fatigue properties of dissimilar spot joints.
This study characterizes the interfaces of Al-steel joints generated by resistance spot welding (RSW) processes. Two types of intermetallic compound (IMC) layers at the interface are characterized ...and discussed. The first type, located in central area of the interface, is composed of tongue-like Fe2Al5 adjacent to the steel and serrated-like FeAl3 adjacent to the Al; the second type, a mixture of FeAl3 and Al, lies in the periphery of the joint interface. Formation mechanisms of the two types of IMC layer observed are proposed and discussed in the paper. The thickness distributions of the IMC layer generated by different welding parameters are predicted based on the dynamic interfacial temperature histories from Al-steel RSW process simulation. The predicted IMC thickness distributions are validated against physical measurements and show good agreement. A bimodal IMC thickness distribution is found when an adequately long welding time is applied. This is found to be related to lower interfacial temperature at the center of Al-steel interface than what in the surrounding area after about 200ms of welding due to strong cooling effect by the electrode.
Multilayered thin pure aluminum (Al) foils and tabs were joined by a recently developed ultrasonic-assisted resistance spot welding (URW) process. The ultrasonic vibration was applied from the onset ...of the preheating current and maintained until the end of the main weld current. Compared with regular resistance spot welds (RSW), solidification cracking and gas porosities were substantially reduced in URW. The nugget center consisted of mixed microstructures of equiaxed dendrites and non-dendritic structures with minimal boundary segregation. Unique wavy structures were observed at the foil side fusion boundary. As the number of foil layers increased from 25 to 75, the amount of equiaxed dendrites increased while that of wavy structures decreased. The sizes of all URW nuggets exceeded the critical diameter, which led to button pullout failure mode. The hardness of weld nuggets and heat affected zone (HAZ) were higher in URW than in RSW. The ultrasonic vibration also reduced HAZ width at the tab of weld stacks.
An ultrasonic-assisted resistance spot welding process, which can improve the quality of aluminum/steel spot-welded joints, has been developed. However, the mechanism of the ...thermal-electrical-mechanical behavior caused by the ultrasonic longitudinal vibration to welding process has not been clarified. In this study, the role and impact mechanisms of ultrasonic longitudinal vibration during the welding process to form joints were confirmed by combining the microstructural characterization of the formed joints with the signal analysis of the process, as well as the analysis of the independent finite element numerical calculation results. Additionally, the interface metallurgical reaction behavior, welding defects, fracture behavior, and joint strength characteristics of ultrasonic-assisted aluminum/steel resistance spot welding joints were comprehensively analyzed, and the results indicated that the sizes of the aluminum/steel nuggets decreased. It could be attributed to the competition among multiple ultrasonic effects. Specifically, ultrasonic vibration decreased the contact resistance between the aluminum/steel sheets, whereas the acoustic cavitation and acoustic streaming effects increased the electrical conductivity of molten steel and thermal conductivity of molten aluminum, respectively. Moreover, ultrasonic vibration promoted the radial creep of molten and near-molten aluminum, which expanded in the effective bonding area between the two workpieces. Furthermore, ultrasonic vibration effectively reduced the thickness of the intermetallic compound layer (<3.0 µm), concurrently inhibited the formation of interfacial welding defects. Finally, the peak tensile-shear load of aluminum/steel joints is significantly increased under multiple ultrasonic optimization mechanisms.
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•The ultrasonic effects are introduced into the computational model for aluminum/steel resistance spot welding process.•The effect mechanisms of ultrasonic vibration on the aluminum/steel resistance spot welding process were explored.•Ultrasonic vibration facilitates the radial creep of molten and near-molten aluminum, which can expand the bonding area.•Ultrasonic vibration decreases nugget sizes by reducing contact resistance, increasing thermal and electrical conductivity.
In this work, resistance spot welding (RSW) was used to weld dissimilar metals of cemented carbide (WC–10Co) and high strength steel (RM80). The mechanical property and microstructure of welded ...joints were analyzed by shear test, scanning electron microscopy and micro X-ray diffraction, establishing the corresponding relationship between the mechanical property of welded joints and microstructure. The results show that with the increase of welding current, the shear strength of welded joints first increased and then decreased, the maximum of which under the optimal welding process was 924 MPa. The characteristics of five interface bonding types were clarified, whose proportion under different welding currents was calculated, and the contribution of each interface bonding type to the performance of welded joints was studied based on the mechanical property and fracture mechanism.
•Maximum shear strength of the WC-10Co/RM80 joints reached 924 MPa.•Formation mechanism of five interface bonding types was analyzed.•The contribution of interface bonding types to the performance of joints was studied.•Three kinds of fracture models were established by analogy.
Abstract The optimal parameters of the resistance spot welding process are discussed, combined with the development and practice of the automobile manufacturing industry. The value, significance, and ...basic theory of the resistance spot welding process orthogonal test are summarized, and the importance of the orthogonal test is recognized. Then summarize the orthogonal test specimen and equipment preparation, test design, and finally analyze the orthogonal test to conclude that the optimal parameters of the resistance spot welding process are optimized, that is, the welding time is 9cyc, the electrode pressure is 1600N, and the optimal welding current is It is 11.5kA, which provides a reference for future manufacturing.
Abstract Zinc-based surface coatings are widely applied with high-strength steels in automotive industry. Some of these base materials show an increased brittle cracking risk during loading. It is ...necessary to examine electrogalvanized and uncoated samples of a high strength steel susceptible to liquid metal embrittlement during spot welding with applied external load. Therefore, a newly developed tensile test method with a simultaneously applied spot weld is conducted. A fully coupled 3D electrical, thermal, metallurgical and mechanical finite element model depicting the resistant spot welding process combined with the tensile test conducted is mandatory to correct geometric influences of the sample geometry and provides insights into the sample’s time dependent local loading. With increasing external loads, the morphology of the brittle cracks formed is affected more than the crack depth. The validated finite element model applies newly developed damage indicators to predict and explain the liquid metal embrittlement cracking onset and development as well as even ductile failure.
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•A novel type of single-sided magnetically assisted apparatus was developed for 7xxx series aluminum alloy RSW process.•Influencing mechanism of induced and external magnetic fields ...on weld macro and microstructure were revealed.•Improving mechanism of external magnetic field on weld performance in lap-shear, cross-tension, and fatigue tests were studied.
In this paper, an external magnetic field was introduced to resistance spot welding (RSW) to improve the weldability of A7N01 aluminum alloy. Comparative studies of the macro- and micro-structures, microhardness, and the static and dynamic mechanical properties between welds produced by traditional RSW and magnetically assisted RSW (MA-RSW) were completed. The results show that the external magnetic field could enable larger nugget diameter, the softened columnar grain zone (CGZ-I), the hardened columnar grain zone (CGZ-II) and the finer equiaxed grain zone (EGZ). As a result, compared to traditional RSW joints, the MA-RSW joints exhibited better strength, improved toughness, and greater energy absorption capacity. This resulted in a transition of the failure mode from an interfacial fracture (IF) to a partial thickness fracture (PTF) in lap-shear tests and a BP fracture in cross-tension tests, respectively. In fatigue tests, the larger nugget diameter, hardened CGZ-II and finer EGZ in the MA-RSW welds can inhibit cracks from propagating from EGZ, but from the softened CGZ to the base metal. This change of fracture mode greatly improved the fatigue life of MA-RSW welds under both high and low load conditions.
