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The influence of welding parameters on temperature distribution during plunging and dwelling phase of friction stir welding (FSW) 2219 aluminum alloy thick plate has not been studied. Improper selection of welding parameters will result in uneven temperature distribution along with the thickness of the weldment, leading to welding defects and ultimately affecting the mechanical properties of the weldment. To achieve the prediction of temperature distribution and the optimization of welding parameters, a simulation process model of FSW 18-mm-thick 2219 aluminum alloy is established based on DEFORM. The validity of the simulation is verified by experiments. With the minimum temperature difference in the core area of the weldment as the target value and weldable temperature range of 2219 aluminum alloy as the constraint conditions, orthogonal experiments are conducted considering the rotational speed, the press amount, the tool tilt angle, the plunging traverse speed and the dwelling time. The results of variance analysis show that the rotational speed and the dwelling time are significant factors affecting the temperature field during the plunging and dwelling phase. Through single factor simulation, the welding parameters during the plunging and dwelling phase are optimized. This study guides the selection of welding parameters of the FSW 2219 aluminum alloy thick plate.

This study investigates the application of the Keyhole–Tungsten Inert Gas Welding (K-TIG) hot-wire filling welding technique with mechanical arc oscillation to weld a 95 mm-thick Ti-6Al-4V titanium alloy plate. The root layer thickness achieved with this technique reaches up to 17 mm, with an average filling thickness of 2.5 mm. The weld bead displays a smooth, shiny appearance, and no significant welding defects are observed in the cross-section of the welded joint. Experimental results show that the welded joint consists of the α phase in different forms, as well as fine α+β microstructures. Compared to the base material, both the weld metal and the heat-affected zone exhibit a lower crystallographic texture strength, with more complex texture types. The impact toughness of the welded joint is excellent, with no significant weaknesses. The impact toughness of the weld metal significantly surpasses that of both the base material and the heat-affected zone. The engagement strengthening effect induced by high-current filling plays a crucial role in enhancing the impact toughness of the weld metal.

While using the subway brings people convenient transportation, The low frequency vibration caused by metro is one of the factors that seriously threaten the physical and mental health of human beings and the working environment. Phononic crystals structure and elastic metamaterials have been favored for the past few years because of their excellent low frequency vibration control properties. In this paper, based on local resonance theory, an elastic metamaterial thick plate structure is designed to attenuate low frequency vibration. Through plane wave expansion method and numerical simulation, the dispersion curve and reduced vibration effect of the thick plate structure are simulated and analyzed, and it is proved that the elastic metamateric thick plate structure opens the bend wave band gap range of 36–110 Hz within the limits of lower frequency below 150 Hz. Finally, a kind of new lower frequency vibration isolation thick plate barrier is designed to minish the effect of low-frequency vibration, which has a potential engineering application foreground in the field of low-frequency vibration control and isolation of subway.

The residual stress is non-uniform in the thickness direction for thick plates jointed by friction stir welding (FSW). An analytical method by using the material flow in the welding process is proposed to solve the non-uniform residual stress of thick plates. The streamline model for the material flow is established in terms of the relationship between stream function and velocity fields in the weld. The cumulative plastic strain is computed by integrating the strain rate along each streamline. The residual stress field is obtained based on characteristic strain theories. Experiments of FSW are conducted for thick plates of aluminum alloy 2024-T3. The residual stresses in the welded region are measured by both X-ray diffraction and the contour method. The relative error of the predicted residual stress in the top surface of the weld is 4.8%. The accuracy of the analytical model can be verified. The analytical and experimental results show that the distribution of residual stress is asymmetric with a conventional “M” shape, and the distance of the two peak stresses is 40.63 mm in the top surface of the weldment. The flow mechanism of material and residual stress in different regions of thick plates by FSW are revealed. The proposed model may be used for the prediction and analysis of the non-uniform distribution of residual stress in thick plates jointed by FSW.

5A06 Aluminum (Al) alloy and AZ31B magnesium (Mg) alloy with 20 mm thickness were successfully butt joined by friction stir welding. In order to control the composition of Al and Mg alloys along thickness direction, an inclined butt joint was designed in this study. The microstructure and phase identification at the interface of Al/Mg joints were examined using scanning electron microscopy with an energy-dispersive spectroscopy and Micro X-ray diffraction. The results indicated that there were two different formation mechanisms of intermetallic compounds at the interface of thick plate Al/Mg joint. The first was constitutional liquation, and eutectic structure consisting of Al12Mg17 and Mg solid solution existed at the top and upper-middle of the Mg side interface. The second was diffusion reaction, and the two sub-layers of Al12Mg17 and Al3Mg2 formed at the lower middle and bottom of the Mg side interface. In addition, the diffusion thickness values of Al12Mg17 and Al3Mg2 layers decreased gradually from the lower middle to bottom of the Mg side interface. As the position changes from the middle to the bottom near the Mg side interface, the diffusion coefficient of Al3Mg2 phase rapidly decreases from 3.14 × 10−12 m2/s to 6.9 × 10−13 m2/s and the diffusion coefficient of Al12Mg17 phase decreases from 6.8 × 10−13 m2/s to 1.5 × 10−13 m2/s.

Optimal selection of friction stir welding (FSW) process parameters is critical for ensuring an even temperature distribution and high weld quality. This study ascertained the impact of process parameters on temperature distribution in the core area of friction stir welded 2219 aluminum alloy thick plate and determined the optimal combination (the range of rotational speed was estimated as 457.15–500.00 r/min, the welding speed was found within the range of 68.50–84.75 mm/min) of these parameters. The FSW process simulation model of 2219 aluminum alloy thick plate was established using DEFORM. The temperature field simulations of plunging, dwelling, welding, and withdrawal phases of FSW were also realized. Thermocouple temperature measurement experiments were performed to validate the model. The impact of welding process parameters on the core area’s maximum temperature and temperature difference was also investigated. The polynomial fitting method was used to establish a prediction model based on maximum and minimum temperatures of the FSW core area. The surface-fitting method was applied to draw the fitting surfaces of maximum and minimum temperatures, which intersected with the upper and inferior limit planes of reasonable welding temperature of 2219 aluminum alloy material, respectively. The intersection line was projected onto the plane with welding and rotational speeds as horizontal and vertical coordinates, respectively, and the optimized combination of welding process parameters was obtained.

Purpose This work attempts to present vibration characteristics of axially traveling moderately thick plates resting on an elastic foundation. The plate is composed of functionally graded (FG) materials, and both its dynamic and kinematic conditions are considered in which the vibration natural frequency and axial velocity involved are taken into account. Methods Based on the Mindlin plate theory and the virtual work principle, the free vibration analysis of an axially traveling moderately thick FG plate is carried out using the finite element method (FEM). Results and Conclusion The validity and accuracy of the present method and related numerical results are verified against the ANSYS software. Some parametric studies on the vibration characteristics of axially traveling moderately thick FG plates are presented in detail, including the effects of axial velocity, gradient index, boundary condition, foundational coefficient and so on. It is confirmed that the gradient index is closely related to material properties, while the axial velocity affects vibration natural frequencies through centrifugal force and Coriolis force. Coefficients of Winkler foundation and Pasternak foundation increase the flexural rigidity of axially traveling moderately thick FG plates, while the viscous coefficient of three-parameter foundation is on the contrary. Also, the boundary conditions influence the vibration behaviors significantly.

The amount of metal materials is gradually increasing with the rapid development of manufacturing industry. Medium-thick plate aluminum alloy is widely used in heavy military vehicles, marine engineering, and other fields for weight reduction or corrosion resistance. However, it is difficult to obtain high-quality deep penetration welds by traditional welding technology to meet the requirements. Based on the welding solution of plate aluminum alloy, this paper summarizes the deep penetration welding process of aluminum alloy plates and analyzes the mechanism and research progress of various process methods. It mainly includes active flux tungsten inert gas welding, pulse melting electrode inert gas welding, swing arc narrow gap GMAW welding, high energy beam welding and laser arc hybrid welding, etc. The welding technology assisted by external magnetic field or ultrasonic field can also realize deep penetration of the weld, and can improve the weld forming, reduce porosity and cracks and other defects. The research on deep penetration welding technology is helpful to promote the high-speed development of plate aluminum alloy welding to automation and intelligence.

The main objective of this study is to uniformly solve the buckling problem of fully clamped (CCCC) orthotropic/isotropic rectangular plates with different thicknesses. The analysis uses the symplectic superposition method. This method describes the buckling problem of orthotropic rectangular moderately thick plates (RMTPs) in the Hamiltonian system for treatment in the symplectic space. First, the governing equations of RMTPs are represented by Hamiltonian canonical equations. Then, the original buckling problem of a CCCC rectangular moderately thick plate (RMTP) is divided into two sub-buckling problems. The variable separation method in the Hamiltonian system is used to calculate the general solutions of these two sub-buckling problems. The symplectic superposition solution of the original buckling problem is obtained by superimposing the general solutions of the two sub-buckling problems. Finally, the analysis results of the buckling load and modal shape of orthotropic rectangular plates under various thicknesses and aspect ratios are presented in numerical examples.

The microstructure and hardness along the thickness direction of a water-quenched, high-strength thick plate with a thickness of 40 mm were investigated with three specimens from the thick plate: surface, 1/4t, and 1/2t (center) thickness, and the phase transformation behavior of the thick plate according to the cooling rate was analyzed through dilatometric experiments. Finally, the cooling rate for each thickness of the thick plate was estimated by comparing the microstructure and hardness of the thick plate along with the thickness with those of the dilatometric specimens. Martensite microstructure was observed on the surface of the water-quenched thick plate due to the fast cooling rate. On the other hand, an inhomogeneous microstructure was transformed inside the thick plate due to the relatively slow cooling rate and central segregation of Mn. A small fraction of bainite was shown at 1/4t thickness. A banded microstructure with martensite and bainite resulting from Mn segregation was developed at 1/2t; that is, the full martensite microstructure was transformed in the Mn-enriched area even at a slow cooling rate due to high hardenability, but a bainite microstructure was formed in the Mn-depleted area owing to relatively low hardenability. A portion of martensite with fine cementite at the surface and 1/4t was identified as auto-tempered martensite with a Bagaryatskii orientation relationship between the ferrite matrix and cementite. The microstructure and hardness as well as dilatation were investigated at various cooling rates through a dilatometric experiment, and a continuous cooling transformation (CCT) diagram was finally presented for the thick plate. Comparing the microstructure and hardness at the surface, 1/4t, and 1/2t of the thick plate with those of dilatometric specimens cooled at various cooling rates, it was estimated that the surface of the thick plate was cooled at more than 20 °C/s, whereas the 1/4t region was cooled at approximately 5~10 °C/s during water quenching. Despite the difficulty in estimation of the cooling rate of 1/2t due to the banded structure, the cooling rate of 1/2t was estimated between 3 and 5 °C/s based on the results of an Mn-depleted zone.