The 2195 Al–Li alloy, as one of the representative third-generation Al–Li alloys, has extensive applications in lightweight aerospace structures. In this paper, the anisotropy in mechanical properties and microstructure evolution of 2195 Al–Li alloy sheets were investigated under a strain rate of 0.01, 0.1, 1 s⁻¹ and a temperature of 440 and 500 °C. Experimental results showed that the hot tensile properties of the 2195 Al–Li alloy sheet exhibited a strong dependence on loading directions. The peak stress (PS) and elongation (EL) along the rolling direction (RD) were larger than the transverse direction (TD). For the tests carried out at 440 °C-1 s⁻¹, the PS values of the sheets stretched along the RD and TD are 142.9 MPa and 110.2 MPa, respectively. And, most of the PS anisotropy values are larger than 15%. The anisotropy in EL is less significant than in PS. All the differences are about 10%. Moreover, dimples in the samples stretched along RD were more and deeper than those along TD at 440 °C. The fracture morphology along RD and TD were similar, and both were cleavage fractures at 500 °C. Particularly, the fractions of high angle grain boundaries (HAGBs) along TD were all about 5% larger than those of RD. And, there were more small-sized continuous dynamic recrystallization (CDRX) grains inside the initial grains and discontinuous dynamic recrystallization (DDRX) grains featured with the local bulge of grain boundaries along TD. This was due to the smaller average Schmid factor and the vertical EL trend of the initial grains when the samples were stretched along TD. A model of grain evolution during the dynamic recrystallization (DRX) along RD and TD was proposed based on EBSD results. The Schmid factor and banded structure had a more prominent effect on the hot ductility of the 2195 Al–Li alloy compared with the degree of DRX, thus presenting a higher EL and better hot ductility along RD.

Boron steel welded tubes show strong potential as blanks in the integrated hot gas forming–quenching process for fabricating complex thin-walled automotive parts. Nonetheless, the non-uniform characteristics of the base metal and the weld in the high-heat welded tube can result in uneven deformation during the bulging process. This inconsistency hampers precise predictions of the deformation behavior of the welded tubes at high temperatures. Accordingly, this research explored the flow characteristics and mechanical properties of PHS1500 boron steel welded tubes. This research was conducted at 850 °C and 900 °C, with strain rates of 0.01 s⁻¹–1 s⁻¹. The Johnson–Cook model was modified for both the base metal and the weld using experimental stress–strain data. Meanwhile, to assess the model precisions, the correlation coefficient r and the average absolute relative error (AARE) were employed. Finally, hot gas forming of PHS1500 boron steel welded tubular parts with complex shapes was predicted through a finite element analysis. This research showed a positive correlation of the strain rate with both the yield and tensile strengths in the base metal and the weld. The average yield strength and tensile strength of the weld were 12.8% and 3.9% higher than those of the base metal, respectively. The r and AARE of the modified Johnson–Cook constitutive model for the base metal’s and the weld’s flow stress were 0.99 and 2.23% and 0.982 and 5.31%, respectively. The maximum deviation in the predictions of the distribution of the wall thickness of a typical cross-section of the formed complex-shaped tubular parts was less than 8%.

In response to the growing demand for complex thin-walled lightweight alloy components in the automotive and aerospace industries, this study investigates the limitations of traditional gas pressure forming technologies. Using 2A12 aluminum alloy thin sheets as the research material, hot high-speed gas bulging experiments were conducted to study the effects of rapid inflation and rapid deflation processes on the forming accuracy, wall thickness, and strain distribution of bulged components. This aims to provide guidance for theoretical research and validate the superiority of the rapid deflation process. The results show that: (1) When forming cup-shaped components at 400 °C, the die-fitting degree of the component formed by the rapid deflation process reaches 89.5% and the minimum corner radius is 2.5 mm. Overall, the forming accuracy of this process is significantly superior to that of the rapid inflation process. (2) Within the temperature range of 400–450 °C, the rapid deflation process successfully formed a spherical-bottom component with a depth of 30 mm, overcoming the cracking defects induced by localized cooling and non-uniform temperature fields in the rapid inflation process, thereby improving the forming limit. (3) Under consistent conditions, the wall thickness uniformity of the sheet formed by the rapid deflation process is significantly higher than that of the sheet formed by rapid inflation, and the wall thickness uniformity improves with increasing temperature. Future work is expected to further enhance the repeatability and stability of forming accuracy and the forming limits of extreme geometries by further optimizing process parameters and expanding the material applicability range. This will provide practical technical support for the manufacturing of lightweight, high-performance aerospace equipment and automotive components.

Large-dimension complex integral thin-shell components are widely used in advanced transportation equipment. However, with the dimensional limitations of raw blanks and the manufacturing process, there are inhomogeneous geometric and mechanical properties at welded joints after welding, which have a significant effect on the subsequent forming process. Therefore, in this paper, the microstructure of welded joints with a sharp property change was accurately characterized by the proposed isothermal treatment method using the BR1500HS welded tube as an example. In addition, an accurate constitutive model of welded tubes was established to predict the deformation behavior. Firstly, the heat-treated specimens were subjected to uniaxial tensile tests and the stress–strain curves under different heat treatment conditions were obtained. Then, the continuous change in flow stress in the direction of the base metal zone, the heat-affected zone and the weld zone was described by the relationship between the microhardness, flow stress and center angle of the welded tube. Using such a method, a continuous constitutive model of welded tubes has been established. Finally, the constitutive model was compiled into finite-element software as a user material subroutine (VUHARD). The reliability of the established constitutive model was verified by simulating the free hydro-bulging process of welded tubes. The results indicated that the continuous constitutive model can well describe the deformation response during the free hydro-bulging process, and accurately predicted the equivalent strain distribution and thickness thinning rate. This study provides guidance in accurately predicting the plastic deformation behavior of welded tubes and its application in practice in hydroforming industries.