To address the deformation issue in friction stir welding (FSW) of aluminum alloy thin-walled structures, a novel method of in-situ rolling friction stir welding (IRFSW) is proposed. The effects of IRFSW on the welding distortion, microstructure and mechanical properties are studied. The results show that the IRFSW can eliminate the flash and ensure the high-quality forming of the joint. The surface grain size of IRFSW joint was obviously refined and a gradient structure with a thickness of about 282 μm was formed on the surface of the IRFSW joint. The surface microhardness of the joint was improved by grain refinement. The tensile strength of the IRFSW joint was 3.3% higher than that of conventional FSW joint. In addition, the distortion degree of IRFSW joint was reduced by 84.8% compared with conventional FSW joint.

Aiming at the problems of low accuracy of traditional ultrasonic thickness measurement methods caused by thin resin-rich layer on the surface of carbon fiber reinforced polymer (CFRP), similar acoustic parameters between the coating and the matrix, and multiple interfaces, a new method based on ultrasonic echo phase derivative spectrum (UEPDS) is proposed to measure the thickness of resin-rich layer on CFRP surface. Based on the multiple reflection rules of ultrasonic waves in multi-layer structures, the UEPDS of coupled medium/coating/substrate three-medium two-interface structure is constructed, and the theoretical relationship between the resonant frequency of UEPDS and coating thickness is identified, so as to overcome the problem that the accuracy of thickness measurement by the traditional sound pressure reflection coefficient amplitude spectrum or phase spectrum is greatly affected by the reference wave and the initial phase of the signal. Combined with calibrated sound velocity, the coating thickness can be accurately determined. The thickness of the resin-rich layer varying from tens to hundreds of microns was measured by an ultrasonic C–scanning system combined with a nominal frequency 25 MHz probe, and the thickness was compared with that observed by laser confocal microscopy. The results show that the 25 MHz probe can effectively measure the thickness of the rich resin layer with a thickness ≥40.7 μm, and the absolute error between the ultrasonic thickness cloud image and the metallographic observation thickness ≤5.1 μm, and the relative error <8.0%. The research shows that the main factor affecting the accuracy of thickness measurement is the presence of fluctuating braided gap residual resin at the resin-rich layer/matrix interface.

The high quality joints fabricated by laser arc hybrid welding have certain differences in the crosssectional geometry of the weld seam. In order to study these differences quantitatively, the back width to surface width ratio (R_w) was proposed. Based on the optimization experiments of 7050–T7451 high-strength aluminum alloy with 3 mm thickness by laser arc hybrid welding, three typical welded seams were selected to investigate the correlation effect of different R_w on the macroscopic formation, microstructure, microhardness and tensile properties of the joints. The results show that, only when the Rw exceeds a certain threshold, the weld width on both sides becomes more uniform, and porosity defects are effectively controlled. The microstructure characteristics of the weld zone from the fusion zone to the center of the weld are fine grains layer, columnar dendritic and large-scale equiaxed grains, respectively. With the R_w increasing, the width of the columnar dendritic structure gradually decreases until it disappears, while, the average grain size at the center of the weld seam gradually increases, and the tensile properties of welded joints increase firstly and then decrease. When the R_w is about 0.70, the tensile properties reach the best, with an average ultimate tensile strength of 390 MPa and elongation after fracture of 2.9%. The tensile fractures present a mixed fracture characteristic dominated by brittle fracture.

In order to realize the effective control of welding quality, the influence of the process parameters on the composite arc voltage in the new laser–plasma arc coaxial hybrid welding of titanium alloy was investigated. An arc electrical characteristic acquisition system was adopted to collect the arc electrical signals in the process of hybrid welding, and the multiple linear regression method was utilized to construct a regression model between the process parameters and the arc voltage, so as to deeply analyze the influence rules of hybrid welding process parameters, such as nozzle height, laser power, and plasma current, on the arc voltage. The results showed that under the conditions set in this experiment, the plasma voltage in the hybrid welding fluctuated dynamically within the range of 18–36 V. Moreover, as the nozzle height, current value, and laser power gradually increased, the arc voltage showed an upward trend. Through the quantitative evaluation of the regression model, the influence of the nozzle height on the arc voltage was the most prominent, followed by the plasma current, and the laser power had the least influence. By observing the changes in the arc morphology, the accuracy of the regression model in judging the weights of the influencing factors was verified. This provided experimental evidence and theoretical basis for further optimizing the welding process.

Aluminum alloys are widely used in areas of aerospace, automobile manufacturing, etc., due to their low density, high strength and corrosion resistance. However, the welding of aluminum alloys is a challenge in manufacturing fields, in which, traditional welding methods have problems such as high heat input and serious deformation. In recent years, laser–arc hybrid welding technology, which combines the advantages of laser welding and arc welding, has become an important method to solve the problems existed in aluminum alloy welding. This paper systematically reviews the research progress of laser–arc hybrid welding for aluminum alloys. Synergistic mechanism and technology advantages of laser–arc hybrid welding are introduced; welding structure and mechanical properties and their influencing factors are analyzed; solutions to a series of problems existed in hybrid welding joint are summarized. Finally, the development directions and application prospects of the laser–arc hybrid welding technology are expected, including automatic and intelligent development, new protective gas and welding filling materials and novel applications of laser–arc hybrid welding technology.

In the traditional laser welding of thin-walled aluminum alloy T-type welds, there are problems such as limited welding station, difficult control of process stability, and easy generation of defects. This study proposes a novel oscillating laser–arc hybrid welding method for aluminum alloy double-seam T-joints to solve the above problems, and welding process test and fluid dynamics analysis of weld pool were carried out. The results show that the oscillating laserarc hybrid welding can effectively inhibit the defects such as porosity, depression, and undercut in the three-sided welding process of single-pass laser welding. In laser–arc hybrid welding process, the transition of the droplet to the molten pool significantly enhances the flow rate, accelerates the heat and mass transfer from the center of the molten pool to the sides, which maintains the stability of keyhole while improving the melt flow characteristics.

With the expectation of high stability in the laser–MIG hybrid welding for magnesium alloy, the real-time monitoring experiments of droplet transfer behavior during the hybrid laser welding process were conducted. A comparative analysis between the droplet transfer behaviors in laser–MIG hybrid welding and conventional MIG welding processes was performed, and the impact of wire feeding speed on droplet morphology and transfer frequency was investigated. The results indicate that the incorporation of a laser heat source significantly enhances the stability of droplet transfer during MIG welding. At the arc power of 2400 W approximately, the droplet transfer process in laser–MIG hybrid welding of magnesium alloy exhibits a globular transfer mode. The changes of wire feed speed have no notable effect on the type of droplet transfer. However, an increased wire feed speed contributes to compressing the arc and enhancing the stability of droplet transfer. Conversely, the excessive wire feeding speed may lead to an undesirable increase in droplet size and a reduction in droplet transfer frequency.

Nickel-based superalloy GH4169 is of special material properties, resulting in large cutting force, high cutting temperature, serious work hardening, tool–workpiece adhesion and tool wear during machining processing of GH4169. Therefore, it is beneficial to controlling tool wear by studying the tool wear mechanism during the process of TiAlN coated carbide tool’s orthogonal turning of GH4169 at different wear stages. Firstly, the orthogonal turning experiments were carried out with GH4169 disc as workpiece and TiAlN coated carbide tool as cutting tool on the CNC lathe, to obtain the tool wear states under different wear stages. Secondly, the tool wear surface was observed by scanning electron microscopy (SEM) and chemical composition of the tool wear surface material was analyzed. Thirdly, the existence of chemical wear of cutting tools was verified by X-ray diffraction (XRD) phase composition analysis. Finally, the tool wear control measures were proposed by combining the full-stage tool wear mechanism and tool wear rate model. The results show that the adhesive wear, abrasive wear, diffusion wear and chemical wear occur during the orthogonal turning of GH4169 by TiAlN coated carbide tools under the selected cutting conditions. The main tool wear mechanisms in the initial wear stage are adhesive wear and abrasive wear while those in the normal wear stage and sharp wear stage are adhesive wear and diffusion wear. Tool wear could be controlled by accelerating decreasing rate of abrasive wear in the initial wear stage or reducing diffusion wear rate in the normal wear stage.

In this study, an integrated analytical and computational framework was established to relate the curing process and loading behavior, and the computational method was systematically verified by carrying out the four-point bending test for AS4/8552 composite, which overcame the previous reported separation between the curing molding analysis and damage mechanics analysis of carbon fiber reinforced plastic (CFRP) composite. During the analysis of curing process, the mechanical strain, thermal expansion strain, and chemical shrinkage strain of the fiber and resin matrix were comprehensively taken into account. Meanwhile, the CHILE model was introduced based on the time-varying evolution of material properties to characterize the changing law of temperature with material parameters, thereby, a coupled thermal–chemical–mechanical analysis model based on time-varying characteristic was established correspondingly. During the mechanical performance analysis, the curing residual stress field was considered as a predefined field, the Hashin failure criterion and Cohesive zone model were used to characterize the intralayer and interlayer damage of the composites, respectively. The results showed that the curing residual stresses not only affect the damage mode and distribution of material, but also reduce the ultimate load of damage failure. The predicted load–displacement curves and damage zone of the CFRP composites under the four-point bending were in good agreement with the experimental results, which verifies the effectiveness of the proposed method in this study.

Si₃N₄ ceramics with high thermal conductivity and high strength were fabricated through gas pressure sintering at 1 MPa N₂ and 1850 ℃ , holding for 4 h in this study. Effects of doping methods (coating and traditional ballmilling) and sintering additive content on the phase composition, relative density, microstructure, mechanical property and thermal conductivity of the as-prepared Si₃N₄ ceramics were systematically studied. The results show that increasing the sintering additive content enhances the second-phase crystallinity, relative density, mechanical property, and thermal conductivity of the Si₃N₄ ceramics. Compared with the traditional ball-milling method introducing sintering additives, the coating method is more favorable to improving the dispersion uniformity of sintering additive, enabling Si₃N₄ ceramics to form a continuous network liquid phase with sintering additive mass fraction of merely 3%, thereby promoting the densification, improving microstructure uniformity, and ultimately enhancing the mechanical property and thermal conductivity of Si₃N₄ ceramics. The sample prepared using the coating method with sintering additive mass fraction of 5% achieved a thermal conductivity of 76.07 W·m^–1·K^–1, fracture toughness of 8.39 MPa·m^1/2 and bending strength of 922.41 MPa, and showing a 13% increase in bending strength compared with the ball-milled sample.

As a forming process with less mold constraints, free bending technology is prone to the occurrence of wrinkling defects caused by instability of thin-walled tubes, which limits its application in high-end manufacturing fields. This study establishes a mechanical model for unstable wrinkling of AA5052 aluminum alloy thin-walled tubes used in aerospace vehicles. Theoretical analysis indicates that the initial geometric micro-defects in the tubes significantly reduce the forming limit under influence of the additional axial thrust. In addition, the mechanical properties of AA5052 aluminum alloy tubes were obtained through uniaxial tensile tests. On the basis of considering initial geometric micro-defects, a finite element model for predicting wrinkling during coreless free bending forming of AA5052 tubes was established using the ABAQUS/Implicit algorithm. The results indicate that the simulation prediction model incorporating initial geometric micro-defects can effectively predict the geometric shape and development trend of tube wrinkling. Finally, accuracy of the model was verified through free bending forming tests. This study is of great significance for understanding the unstable wrinkling behavior in free bending forming and improving the control level in manufacturing process.

Due to the large size and small stiffness of aircraft skin, it is easy to produce machining deformation during cutting processing. Aiming at the problem of mirror machining deformation of skin, a deformation prediction flexible method based on substructure technology is proposed. This method divides the whole thin-walled part into two parts, and reduces difficulty of solving the deformation model of the whole thin-walled part by coupling the deformation models of the two parts. On the basis of considering the continuity of tool path deformation, the traditional iterative method is still used to predict machining deformation at the initial cutting position while in other cutting positions, convergence depth of the previous cutting position is used as the initial iterative value. Compared with the traditional iterative prediction method of machining deformation, the proposed method greatly improves the convergence rate. Moreover, effectiveness of the proposed method was demonstrated through finite element simulation and mirror machining experiments, with overall computational time and iteration times reduced by 46.15% and 41.94%, respectively.