Process Characterizations of Ultrasonic Extruded Weld-Riveting of AZ31B Magnesium Alloy to Carbon Fiber-Reinforced PA66.

Traditional metal-plastic dissimilar welding methods directly heat the metal workpiece, which may cause potential thermal damage to the metal workpiece. Ultrasonic extruded weld-riveting (UEWR) is a relatively new method for dissimilar joining of carbon fiber-reinforced thermoplastic (CFRTP) and metal. In this method, the CFRTP workpiece is melted using the ultrasonic effect and is squeezed into prefabricated holes in the metal workpiece to form a rivet structure. In this method, the metal workpiece is not directly heated, and potential high-temperature losses can be avoided. This paper investigates the process characterizations of UERW of AZ31B magnesium alloy to carbon fiber-reinforced PA66. The process parameters are optimized by the Taguchi method. The joint formation process is analyzed based on the fiber distribution in the cross-sections of joints. The effects of welding parameters on the joint microstructure and fracture surface morphology are discussed. The results show that a stepped amplitude strategy (40 µm amplitude in the first stage and 56 µm amplitude in the second stage) could balance the joint strength and joint appearance. Insufficient (welding energy < 2600 J or amplitude-A < 50%) or excessive (welding energy > 2800 J or amplitude-A > 50%) welding parameters lead to the formation of porous defects. Three fracture modes are identified according to the fracture surface analysis. The maximum tensile shear strength of joints at the optimal parameters is about 56.5 ± 6.2 MPa.

Effect of Process Parameters on Joint Performance in Hot Pressure Welding of 6061 Aluminum Alloy to CF/PA66.

Polymer-metal hybrid structures combine the merits of polymer and metal materials, making them widely applicable in fields such as aerospace and automotive industries. However, the main challenge lies in achieving efficient and strong connections between the metal and polymer components. This paper uses the jet electrochemical machining (Jet-ECM) method to customize the surface morphologies on 6061 aluminum alloy (AA6061) sheets. The connection between AA6061 and carbon fiber-reinforced PA66 (CF/PA66) is then achieved through hot pressure welding (HPW). The effects of aluminum alloy surface morphology, welding force, and welding time on the mechanical properties and microstructure of the joint are investigated. The optimal process parameters are determined by the design of the experiment. The results show that the aluminum alloy surface morphology has the greatest impact on the mechanical property of the welded joint. The optimal process parameters are surface morphology with wider, shallower, and sparsely distributed grooves on the aluminum alloy surface, the welding force is 720 N, the welding time is 12 s, the welding temperature is 360 °C, the cooling time is 16 s, and the optimal peak load of the joint is 6690 N. Under the optimal parameters, the fracture morphology in the AA6061 side is almost entirely covered with CF/PA66. The joint experiences cohesive failure in most areas and fiber-matrix debonding in a small area.

Enhancing Mechanical Properties: Exploring the Effect of Annealing Temperature on Wire Arc Additively Manufactured High-Strength Steel.

This study investigates the mechanical properties of exceptionally high-strength steel produced by wire and arc additive manufacturing (WAAM), using the 304 stainless steel wire and the low carbon wire (LCS). The study found that annealing treatment can enhance the steel's mechanical properties. The microstructure in the LCS layer changed from ferrite to bainite and then to a mixture of austenite, pearlite, and bainite with increasing annealing temperature. In contrast, the SS layer retained its martensitic structure, albeit with altered lath sizes. The annealing treatment also improved the orientation of the grains in the steel. The optimal annealing temperature observed for the steel was 900 ℃, which resulted in a maximum tensile strength of 1176 MPa along the Y direction and 1255 MPa along the Z direction. Despite the superior mechanical properties, the LCS layer still exhibited failure during tensile testing due to its lower hardness. The study suggests that annealing treatment can be a useful technique for enhancing the mechanical properties of high-strength steel in WAAM applications.

Prediction of Resistance Spot Welding Quality Based on BPNN Optimized by Improved Sparrow Search Algorithm.

Accurately predicting resistance spot welding (RSW) quality is essential for the manufacturing process. In this study, the RSW process signals of 2219/5A06 aluminum alloy under two assembly conditions (including gap and spacing) were analyzed, and then artificial intelligence modeling was carried out. To improve the performance and efficiency of RSW quality evaluation, this study proposed a multi-signal fusion method that was performed by combining principal component analysis and a correlation analysis. A backpropagation neural network (BPNN) model was optimized using the sine-chaotic-map-improved sparrow search algorithm (SSA), and the input and output of the model were the variables after multi-signal fusion and the button diameter, respectively. Compared with the standard BPNN model, the Sine-SSA-BP model reduced the MAE by 42.33%, MSE by 51.84%, and RMSE by 31.45%. Its R2 coefficient reached 0.6482, which is much higher than that of BP (0.2464). According to various indicators (MAE, MSE, RMSE, and R2), the evaluation performance of the Sine-SSA-BP model was better than that of the standard BPNN model. Compared with other models (BP, GA-BP, PSO-BP, SSA-BP, and Sine-PSO-BP), the evaluation performance of the Sine-SSA-BP model was best, which can successfully predict abnormal spot welds.

Microstructural Characterization and Mechanical Behavior of NiTi Shape Memory Alloys Ultrasonic Joints Using Cu Interlayer.

NiTi shape memory alloys (SMAs) are a class of functional materials which can be significantly deformed and recover their original shape via a reversible martensitic phase transformation. Developing effective joining techniques can expand the application of SMAs in the medical and engineering fields. In this study, ultrasonic spot welding (USW), a solid-state joining technique, was used to join NiTi sheets using a Cu interlayer in between the two joining sheets. The influence of USW process on the microstructural characteristics and mechanical behavior of the NiTi joints was investigated. Compared with conventional fusion welding techniques, no intermetallic compounds formed in the joints, which is extreme importance for this particular class of alloys. The joining mechanisms involve a combination of shear plastic deformation, mechanical interlocking and formation of micro-welds. A better bonding interface was obtained with higher welding energy levels, which contributed to a higher tensile load. An interfacial fracture mode occurred and the fracture surfaces exhibited both brittle and ductile-like characteristics with the existence of tear ridges and dimples. The fracture initiated at the weak region of the joint border and then propagated through it, leading to tearing of Cu foil at the fracture interface.