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Ultrasonic welding is known as "green welding manufacturing technology" because of its fast, energy-saving, clean and pollution-free technical characteristics. Therefore, ultrasonic welding technology has a wide application prospect in aerospace, automobile and other fields. In this study, ultrasonic welding between AZ31B magnesium and pure copper are carried out. The fracture, microstructure and tensile properties of the joint are studied, and its connection mechanism is analyzed. The finite element analysis model of magnesium-copper ultrasonic welding process is established. The analyses of test results show that the fracture mode of magnesium-copper ultrasonic welded joint is interface-type fracture. The joint strength reaches the maximum value of 3798 N. The ultrasonic connection between magnesium alloy and copper is mainly realized by the interface diffusion layer formed in the welding process. The main component of the interface diffusion layer is mg2cu. The growth trend of interface diffusion layer is revealed. The analyses of FEM results show that the heat is generated in the central area of the solder joint, and then transferred around. The maximum temperature at the interface can reach 550 ℃. The distribution law of temperature field and plastic deformation field of joint are revealed.

When welding high-strength steel and ultra-thin plates, traditional resistance spot welding has technical problems such as a narrow process window and difficulty in ensuring both welding strength and forming quality, making it one of the bottlenecks in the manufacture of high-end structural parts in the fields of vehicles, aviation and aerospace. The core reason is that the traditional spot welding thermal cycle mode is single, the energy is highly concentrated, and the controllability is poor. Therefore, there is an inconsistency between its energy distribution and nugget quality. In view of the above difficulties, a new idea of resistance spot welding of special-shaped electrodes based on energy distribution design is proposed. By inlaying insulating ceramics and other materials on the electrode end face, a "composite annular electrode" is prepared to realize the regulation of energy distribution in the welding process. In this paper, the thermo-electric-structural coupling FEM of a new composite electrode is established to reveal the detailed influence of the diameter of the ceramic core on the joint forming and thermal distribution. And the optimal ceramic core diameter is optimized for ultra-thin plates and high-strength steel plates commonly used in automobiles.

A clinch-resistance hybrid spot welding method was presented to join Al and steel. The nugget formation was analysed via microstructure observation and numerical simulation. A cup section nugget wa...

This paper presents a test device to explore the influence of geometric attribute of the contact surface on friction coefficient along with sliding speed and contact pressure. Friction tests were conducted on a third-generation high strength steel QP980. The friction coefficients for different surface curvatures, contact pressures and sliding speeds were calculated and the influences of these factors were analyzed. The formula for calculating the friction coefficients between curved contact surfaces was derived. The relationship between bending induced surface roughness increase and friction coefficient was established. An enhanced friction coefficient model with pressure, velocity and curvature dependence was proposed. The enhanced friction model was applied to simulate the stamping of an automotive part and a better correlation was achieved.

A novel clinch-resistance spot welding method of dissimilar materials was presented. A group of punch-die electrodes was used to weld 1-mm 5083 Al alloy and 1-mm galvanized steel sheets. Microstructure and mechanical properties of the welded joints obtained with punch-die electrodes were studied. Stress is analyzed by numerical simulation, and the tensile shear strength distribution under different welding parameters is analyzed using artificial neural network. A cup section is formed after welding, which results in 3D connection of the bonding interface. Stress concentration on the steel/Al contact surface locates on the connection between the punch tip and die tip. The melt zone is mainly formed at the nugget edge, and a relatively small melting area is generated at the central area on the Al side. The maximum failure load can be increased to 4.5 kN. The range of parameters for obtaining high strength is relatively wide in clinch-resistance spot welding, and the interaction of current and time has a significant effect on the strength.

The extensive application of automobile high-strength steel requires high welding strength. A composite ceramic-filled annular electrode is designed based on the concept of controlling heat distribution and changing the nugget-growth mode. DP980 high-strength steel sheets were resistance welded to explore the effect of the annular electrode, and a traditional resistance spot electrode was also used for comparative analysis. The formation and mechanical properties of the nugget were analyzed. The results show that the resistance annular welding formed an annular nugget whose plan view is similar to the end face of the electrode. The annular nugget had a smaller surface indentation depth than the spot-welded nugget. Under the same external diameter of the end face of the electrode, applying the annular electrode produced a nugget area larger than that produced by a traditional circular end face electrode, thereby providing higher tensile and peeling strengths within a larger welding process window. The numerical simulation results of resistance annular welding (RAW) indicated that no current passed in the ceramic filled area; a small annular liquid nugget formed at the initial stage, and then grew inward and outward simultaneously during the welding process. Keywords: Ceramic-centered annular electrode, Resistance welding, High strength steel

Aluminum and steel are widely used in automotive and aerospace industries. As a new type of solid-phase welding, ultrasonic spot welding is an effective way to achieve joints of high strength. In this paper, ultrasonic welding was carried out on aluminum-steel dissimilar alloys to investigate the influences of welding parameters on joint strength. Designed and conducted a 3-factor, 3-level comprehensive test. The analyses of test results show that there are 3 kinds of fractures on the welding joint with different welding parameters. The highest strength can reach 3910 N. Clamping force and vibration amplitude not significantly impact the tensile strength. Vibration time significantly impact the tensile strength although its significance level is close to the threshold. The interaction between welding parameters all can significantly impact the tensile strength. The artificial neural network optimized by Genetic Algorithm was used to establish an analytical model. The supplemental experiment and residual analysis were conducted to verify the accuracy of the analytical model. The analytical model show that with the increase of clamping force, the changes of optimal and minimum strength are limited, but the range of welding parameters to obtain a higher strength change significantly; the optimal welding parameters from lower vibration amplitude and higher vibration time shifts towards to higher vibration amplitude and shorter vibration time gradually; for 0.3 Mpa clamping force, the influences of vibration amplitude and vibration time on tensile strength are not significant.

Considering the poor formability of aluminum alloys at room temperature, this study proposes a stamping technique assisted by arc pretreatment that locally modifies the material properties. V-shape bending tests are conducted on the arc-treated specimens. The formability (bendability in particular) of 6061-T6 aluminum alloy is significantly improved by arc pretreatment and the springback is reduced as well. The reasons for formability improvement and springback reduction are analyzed through the microstructure, mechanical property, and fracture morphology of the heat-affected zone. The hardness at different locations within the heat-affected zone before and after bending is also tested. Finally, the advantages of arc pretreatment over other traditional forming processes at elevated temperatures are explained.

This research explores the joining between dissimilar alloys (magnesium alloy and titanium alloy) by ultrasonic spot welding. The tensile shear test shows that the joint strength increases with energy input. The fracture initiates inside magnesium alloy, indicating a high joining strength at the weld interface. Banded grain-refinement is found at the interface on the magnesium alloy side, neither transition layer nor inter-metallic compound layer is identified though. The interfacial temperature exceeds the temperature range for liquefying magnesium alloy. The precipitated aluminum from the liquid-phase magnesium alloy plays a bridging role in ultrasonic welding of magnesium alloy to titanium alloy.

A resistance welding method that uses a composite ceramic-centered annular electrode (RAW) was adopted to improve the weldability of high-strength steel. The design idea was to increase the strength of welded joints by the formation of a large nugget with low indentation depth. The strength and the nugget formation of joints produced by the RAW, and the traditional spot welding (RSW) were comparatively investigated by the microstructural, artificial neural network, and finite element model analyses. The highest failure load reached 22.3 kN in the RAW, and the strongest influence on the strength was welding time, followed by welding current, and electrode force at the end. The interaction between these welding parameters significantly influences the strength of joints in the RAW but not in the RSW. Based on the ANN models, a detailed relationship between the parameters and the strength in RAW were obtained, which also determined that the optimal window of welding parameters in the RAW was larger than that in the RSW. The FEM model analysis showed that the annular nugget was generated first, then expanded outward and inward in RAW, and finally completely fused in the nugget center. The mode of heat transfer and the nugget formation could contribute to better dissipation of the resistance heat generated in the RSW. This “soft” heat distribution yields a large nugget with low indentation depth.

The advancement in the application of light alloys such as magnesium and titanium is closely related to the state of the art of joining them. As a new type of solid-phase welding, ultrasonic spot welding is an effective way to achieve joints of high strength. In this paper, ultrasonic welding was carried out on magnesium–titanium dissimilar alloys to investigate the influences of welding parameters on joint strength. The analysis of variance was adopted to study the weight of each welding parameter and their interactions. The artificial neural network (ANN) was used to predict joint strength. Results show that in ultrasonic welding of magnesium and titanium alloys, clamping force is the most significant factor, followed by vibration time and vibration amplitude; the interactions between vibration time and vibration amplitude, and between vibration amplitude and clamping force also significantly impact the strength. By using the artificial neural network, test data were trained to obtain a high precision network, which was used to predict the variations of joint strength under different parameters. The analytical model predicts that with the increase in vibration time, the increase in optimal joint strength is limited, but the range of welding parameters to obtain a higher joint strength increases significantly; the minimum joint strength increases as well; and the optimal vibration amplitude expands gradually and reaches the maximum when the vibration time is 1000 ms, then shifts toward the low end gradually.