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A novel technology combining forming and reaction synthesis has been developed to manufacture NiAl alloy sheet components which are difficult to form using conventional fabrication approaches. A semi-circular shaped NiAl sheet component was successfully fabricated using forming-reaction synthesis integrated process (FRSIP) with laminated Ni/Al foils. Through microstructure characterization, the mechanism of the reaction synthesis of laminated Ni/Al foils was studied for manufacturing homogenous components. The process was performed at 650 °C under the pressure of 15 MPa for 4 h to consume Al layers and produce the multilayered composite of Ni/Ni2Al3/Ni, and further annealed at 1200 °C under the pressure of 25 MPa for 1 h to produce fully dense and homogeneous NiAl alloy. Based on electron back-scatter diffraction (EBSD) analysis, the NiAl sheet contains inter-laminated coarse-grain layers (CGLs) and fine-grain layers (FGLs), which formed at original Al foil layers and original Ni foil layers, respectively. The grain sizes of the CGLs can be adjusted by controlling the thickness of the original Ni foils. The mechanical properties of NiAl sheet were studied by means of nano-indentation tests and tensile tests, which showed that the weak grain boundary weakened the Hall-Patch (H-P) phenomenon. The bimodal grain structure was a main factor influencing the performance of plastic deformation at high temperature.

A combination method of beneficial wrinkle and preform shape is proposed to solve the problem of non-uniform thickness distribution during hydroforming of a variable diameter tubular component. The effect of loading path for the hydroform part and the preform shape are simulated by LS-DYNA. At the same time, the wall thickness deviation of the maximum and minimum of the hydroformed part is considered as the optimal target and the loading path for the preform shape is optimized to obtain the beneficial wrinkles by response surface methodology. Simultaneously, hydroforming experiments were conducted to verify the simulation results. Study shows that the loading path plays an important role in the forming of the beneficial wrinkles, which influence the cracking and the wrinkling defects. Only the loading path is appropriate can the beneficial wrinkles be formed and the wrinkles are flattened in the subsequent calibrating process. Response surface methodology is an effective way to obtain the optimal loading path, and the desired loading path can be achieved by controlling the relationship of the axial feeding and the internal pressure.

An interesting process of double-sided tube hydro-bulging was proposed to provide a beneficial three-dimensional stress state in the deformation zone of the tube, so as to delay the occurrence of bursting on the tube. Previously proposed forming limit theory models with consideration of through-thickness normal stress found that the external pressure could lead to a deferred occurrence of plastic instability, but it has not been confirmed experimentally. In this article, the tensile plastic instability of tubes under double-sided pressures is further assessed based on the classical plastic instability theory. However, it is seen that the occurrence of plastic instability has not found delay when high external pressure was exerted on the outside surface of tube simultaneously, which is opposite to the previous forming limit models. In addition, an experiment investigation about double-sided tube hydro-bulging is conducted to verify the theoretical results, and the experimental results show that the external pressure has hardly any influence on forming limit strain of the 2A12 aluminum alloy tube before the occurrence of necking. Moreover, the contradiction between our results and the previously proposed forming limit theory models is that the previous models ignored the thickness item in the equilibrium equation.

The deformation behavior was characterized using uniaxial tensile and free bulging testing. Digital Image Correlation (DIC) system was used to probe the full strain fields during the whole bulging process. Thickness distribution of the friction stir welded (FSW) sheet was analyzed and compared with the base metal. The flow stress of FSW joint was lower than that of base metal at the temperature of 400 °C and initial strain rate of 0.001 s−1. The ultimate tensile strength of FSW joint was about 70% of the base metal. The deformation was concentrated in the nugget zone of the weld during both uniaxial tensile tests and free bulging tests at high temperature, exhibiting significant inhomogeneous deformation characteristic. The bulging height of FSW sheet was only 50% of the base metal. The directions of major strains of weld zone and adjacent base material in the FSW sheet were vertical to each other during bulging tests. Such an incompatible deformation behavior resulted in the poor formability of FSW sheet compared with base metal.

An ellipsoidal shell is first welding assembled by 12 pieces of lateral petal and 2 pieces of polar plate, and then hydro-formed into the needed dimension. In order to analyze the effect of welding distortion of preform shell on dimension accuracy of ellipsoidal shell, welding assembly and subsequent hydro-forming of ellipsoidal shell with the axis length ratio 2.2 were conducted by experimental research along with simulation. Welding distortion was experimentally evaluated for every sequential number of weld seams, and the displacement of each weld seam was recorded by 3D-video measurement. It is shown that the radial displacements on the welding seams are inward the radial direction, and the magnitudes of deformation increase with the progress of welding assembly. Considering the welding distortion of preform shell, simulation was conducted on hydro-forming process; latitudinal stress distribution and thickness distribution were given. An experiment on hydro-forming process was carried out, and the axis length variation, volume variation, and residual stress on the weld seams were stated. It is shown that the latitudinal stress, thickness on lateral petals, and long axis variation are asymmetrical at the early stage of deformation, but the wrinkling does not occur. With the increase of internal pressure, sectional profiles at latitudinal direction will trend to circle and a sound symmetric ellipsoidal shell has been obtained. The magnitude of residual stress after hydro-forming is very small and sometimes is compressive, which can significantly improve the ability of resist stress corrosion for pressure vessel. It is proved that the welding distortion can be eliminated by severe plastic deformation and it has less influence on the forming accuracy. However, it may be considered when the plastic deformation is slight such as hydro-forming of sphere.

Numerical simulation and experimental methods were conducted to study the non-uniform thickness during hydroforming of a rectangular cross-sectional component by using a bent tube, which is thickened inside and thinned outside. A method of changing the contact sequence of the tube to the die surface is proposed to improve thickness distribution of hydroformed part. There are four contact sequences, Side-and-Side (SS), Side-and-Fillet (SF), Fillet-and-Side (FS) and Fillet-and-Fillet (FF), that are proposed through the preform shape for a rectangular section. The effect of contact sequence on thickness distribution was studied. The results show that SF or FF contact sequence makes the fillet corner contact with the die surface first and suppresses the further thinning in hydroforming. On the contrary, SF or SS contact sequence makes the straight side of the bend inside contact with the die surface first and benefits the full deformation of the thickening region in hydroforming. Among them, the SF contact sequence is the best for the uniformity of thickness, and SF and FF contact sequences are useful to ensure the minimum thickness of the section and help to avoid cracking defects. On the basis of it, two contact sequences, SS and FF, were applied to an instrument panel bar, respectively. There is a cracking defect in the circular section for the SS sequence, while there is no defect in the straight and circular sections for the FF sequence. And the sound part is successfully developed and applied to the assembly of the instrument panel bar of Chrysler 300C car in mass production.

To avoid out of round during hydro-forming of the orange shell with small polar plates, a new preform shell with basketball type has been designed before hydro-forming. The theory for trending spherical shell from single-curvature preform shell was analyzed. The results demonstrated that the performance difference between original sheet and weld seam does affect the deformation behavior. The roundness was analyzed by numerical simulation for hydro-forming of the basketball and orange spherical shells; and the influence of preform type was discussed on out-of-roundness. It is shown that 0.65% out-of-roundness on the 90° cross section of orange preform shell still existed when the internal pressure made the basketball preform shell to a sound circle on each section. Furthermore, an experiment was conducted on hydro-forming of basketball and orange shells with diameter 160 mm. The deformation of the shell shapes, variations of the diameters, volume change, and thickness distributions were measured in the experiment. The basketball shell has more accurate shape and uniform thickness than orange shell under the same internal pressure. It is proven that hydro-forming of the basketball preform shell is reasonable and this new type is suitable for manufacturing of the spherical shell.

To overcome the poor plastic deformation performance of AA2219 aluminum alloy sheet and its weld seam at room temperature, an integral hot gas pressure forming (IHGPF) process for a combined welded ellipsoidal shell was proposed. A simulation of the IHGPF process was conducted to analyze the axis length variation and thickness distribution during the forming process of the combined welded ellipsoidal shell at elevated temperature. The results demonstrated that lengths of the short and long axes were 150 mm and 220 mm, respectively, and that maximum wall thinning occurred at the pole. Furthermore, an experiment was conducted using IHGPF, and the forming accuracy was measured by three-dimensional video technology. A sound ellipsoidal shell with final axis length ratio of 1.5 was obtained with a shell diameter accuracy of more than 99.3%. It was experimentally proven that an aluminum alloy ellipsoidal shell can be formed using the proposed IHGPF technology.

In situ 3.5 vol% TiBw whisker reinforced TiBw/TA15 composite with a novel network architecture was successfully fabricated by reaction hot pressing (RHP) method. In order to improve the high temperature mechanical properties of the composite, solid solution and aging treatments with different parameters were carried out. After sintering, the composite formed a net-like microstructure. The strength of composite was improved by the effect of whisker-rich boundary and the interconnected whisker-lean matrix retained its ductility. The elastic modulus and hardness of different phases were tested by nanoindentation for better understanding the strengthening mechanism. The ultimate tensile strength at 600–700 °C of the composite showed the highest value when the solution temperature is 1000 °C followed by aging treatment, which was caused by the distribution of a few residual primary α phases on the boundary and in turn the increasing of volume fraction for the reinforcements. Furthermore, the size and fraction of fine α+β phases increased with increasing of aging temperature after 1000 °C solid solution treatment, leading to the increasing of ductility and decreasing of strength for the composite tested at 600–700 °C. The above results showed that the composite with novel network architecture could be strengthened by heat treatments at high temperature environment, e.g. the ultimate tensile strength could be improved more than 200 MPa at 600 °C, and more than 100 MPa at 700 °C.

During tube hydroforming process, fracture often occurs on the aluminum alloy tubes due to their low plasticity and poor formability. Therefore, the topic about formability improvement of hard-to-form tubes is of great importance and attraction in the field of tube forming. In this paper, the 5052 aluminum alloy tube was covered with a 304 stainless steel tube with good plasticity as a supporting in order to enhance its formability. Then, the double-layered tubes were hydrobulged freely under the internal pressure simultaneously. It is shown that the bulging ability of inner 5052 aluminum alloy tube can be enhanced dramatically by the outer supporting tube. The ultimate expansion ratio can be improved from 11.57 to 30.86 %, corresponding to an approximate increasing rate of 167 %. The outer supporting tube can make the 5052 aluminum alloy tube achieve a greater thickness reduction before fracture occurrence. Moreover, the outer supporting tube has also an influence on the fracture behavior of 5052 aluminum alloy tube. The microscopic dimples on the 5052 aluminum alloy tube fracture surface have become bigger and more flat, corresponding to a reduction of the number and area of microscopic dimples. The equivalent fracture strain of 5052 aluminum alloy tube is deceased when the outer supporting tube was used. In brief, the formability of 5052 aluminum alloy tubes can be enhanced dramatically by the outer supporting tube, and the deformation uniformity can also be improved.

Bending springback plays an important role in hydroforming of curved hollow components, and the effect will be more apparent with the increase of the strength of the material. In order to predict and eliminate the effect of springback on hydroforming process, springback of DP590 welded tube was investigated in computer numerical control (CNC) bending process using theoretical analysis, numerical simulation, and experimental methods. The effects of the bending angles, the diameter-thickness ratio d/t, and the relative bending radius R/d on springback are studied, and the influence factor of the weld position is considered. The theoretical and experimental results show that the springback of the DP590 welded tube with 65 mm in diameter and 2.6 mm in thickness varies within the range from 4.0 to 4.9 % and the amount of springback is influenced by the tube diameter and thickness. The springback reduces from 7.0 to 3.5 % when the diameter-thickness ratio is increasing from 10 to 40. On the contrary, the springback increases from 3.7 to 7.2 % when the relative bending radius is increasing from 1.2 to 4.0. The effect of weld position on springback is very little, but it has a negative effect on defects of hydroforming and wall thickness distribution. It is liable to crack when hydroforming if the weld locates on the outside or neutral layer of the bend. Finally, springback rules and weld effect are applied to form a control arm. A sound part had been successfully manufactured to avoid flash and crack defects considering the appropriate springback compensation and weld position.

Thickness distribution is always an important criterion in evaluating the deformation uniformity of sheet metal shells. In order to study the influence of double-sided liquid pressure on the thickness distribution of aluminum alloy curved shells, a dedicated experimental setup was designed to carry out double-sided sheet hydroforming processes. The thickness distribution of the formed shells were measured and compared under different loading paths. The deformation mode and the stress state were analyzed using simulation results to make a deeply understand on the mechanism of the thickness variation. It is shown that the forward pressure plays a slightly negative role in the thickness distribution of the formed parts. The deformation mode of the shells varies little when added forward pressures in the current experiments. The Von Mises stress and the effective strain of the components are improved when conducting the double-sided hydroforming process. The larger thinning phenomenon when adding forward pressure on the blank is mainly caused by the increasing of reduced third principle stress. This paper can offer suggestions and guides to the future studies about the double-sided sheet hydroforming process.

The reverse deep drawing of a plate is more difficult than that of a sheet due to the bending effect. In order to solve this difficulty, experiments and simulations were conducted to investigate the deformation behavior of forming a deeper cup using a 4.5-mm-thickness 5A06 aluminum alloy plate. Three die corner shapes were used to analyze the bending effect on the fracturing. The stress and strain distribution considering the bending effect was obtained by the simulation. It is shown that the fracture occurs at the inside flange corner and it can be avoided by changing the die corner shape. The limit drawing depth can be increased from 79 to 118 mm as the reasonable die corner shape was used. The reason for the fracturing is that a bigger tensile stress was induced by the bending effect at the inside flange corner, which leads to a stress gradient along the thickness. When the semicircle die corner shape was applied, the increment of the tensile stress at the inside area of the flange can be significantly reduced so that a deeper cup can be formed.

In order to form the needed prolate ellipsoidal shell with higher dimension accuracy, it is essential to develop an optimal pre-form shape before hydro-forming. A group of numerical simulation according to the optimal Latin hypercube design (Opt LHD) was first conducted on the combined prolate ellipsoidal shells, and the mathematical response models of axis lengths were developed. And then based on the adaptive simulated annealing algorithm, the reverse geometric modeling process was carried out and the possible pre-form shapes were given. Finally, an experimental verification was conducted to evaluate the reverse geometric modeling process, and the comparison between reverse design and experimental data was mainly discussed. It is shown that the dimension deviation between experiment and reverse design is less than 1 %. It is also experimentally proved that the needed prolate ellipsoidal shell can be formed by reversely designing an optimal pre-form shell.

Tube hydro-bulging test is a specialized method to obtain the mechanical properties of tubes when they are deformed under bi-axial stress states. However, the normal stress cannot be ignored in double-sided tube hydroforming process. In order to investigate the mechanical properties of anisotropic thin-walled tubes under three-dimensional stress state, an analytical model for stress component calculation for fixed-end tube under internal and external pressures was proposed. Furthermore, the equivalent stress and the equivalent strain were derived using the Hill 1948 yield criterion through plastic increment theory. A thin-walled AA5052-O aluminum alloy tubes were bulged under different external pressures using a dedicated testing apparatus for double-sided tube hydro-bulging tests. Then, hardening curves considering anisotropy were obtained for each external pressure condition, respectively. It is shown that the strain hardening exponent of AA5052 tube shows a slight increase with the increasing external pressure, and the external pressure of 85 MPa has little or no effects on the hardening behavior of tubes. Moreover, the anisotropy has a little effect on the strain hardening exponent, but has an obvious influence on the strength coefficient of the AA5052 tube. Therefore, for the measurement of the AA5052 tube’s mechanical properties under three-dimensional stress state, the effect of external pressure can be ignored but the anisotropy of tubes must be considered.

Excellent mechanical properties and satisfactory corrosion resistance were achieved in an Al–Zn–Mg–Cu alloy via non-isothermal ageing (NIA) treatment. The precipitation and age-strengthening were elucidated by combining the TEM observing, DSC analysis and the mechanical properties testing results. The corrosion resistance was evaluated based on the measured electrical conductivity. The effect of staring temperature (Ts) and the cooling rate (Rc) of the NIA processes on the properties was systematically investigated. The continuously decreasing temperature is found inhibit existing precipitates’ coarsening and also induces secondary precipitation. High Ts and low Rc bring about high conductivity and low hardness. Extra hardening together with a conductivity decrease occurs at the later stage of NIA processes due to the forming of fine secondary precipitates. High strength combined with high conductivity can be obtained by setting Ts at the 180–190 °C range and Rc at the 10–20 °C/h range. An optimized NIA process (cooled from 190 to 100 °C at 20 °C/h) provides higher strength and comparable SCC resistance within a halved processing time by looking the typical T74 ageing as a reference.

Due to the requirement of lightweight in the automotive industry, aluminum alloy components with irregular cross sections have been used for body-in-white parts. In order to obtain an aluminum alloy cross member with uniform thickness distribution and acceptable dimension accuracy, a hydro-forming process of a 6063-T4 aluminum alloy cross member was studied by experimental research and numerical simulation. To avoid severe thinning and bursting during hydro-forming, the design of experiments according to a central composite design method was carried out, and the significance of pre-form structural parameters was discussed on thinning. According to the optimum pre-form shape, experimental researches were then conducted on thickness distribution of typical sectional profiles and dimension accuracy. It is shown that the maximum thinning is 14 %, which is located on sectional profile B-B. The deviation of circumferential dimension accuracy along the axial direction is 0.33 %. The maximum dimensional deviation at sectional profiles A-A and B-B is 0.19 and 0.22 mm, respectively; accordingly, the dimension accuracy along the width direction is 0.4 and 0.31 %, respectively. Finally, a sound hydro-formed cross member is obtained.

With the increasing use of advanced high strength steel for automotive components, hydro-formed hollow components have the advantage of both high strength and high stiffness. In order to manufacture a 780 MPa torsion beam satisfied with both improved safety and lightweight, hydro-forming process of 780 MPa torsion beam was studied by experimental research and numerical simulation. Pre-form design according to central composite method was carried out to avoid forming flash and bursting during hydro-forming. Response surface model of the effect of pre-form structure on thickness distribution was developed, and significance of structural parameters on the response value was discussed. According to the genetic algorithm, an optimum pre-form shape has been obtained. An experiment was carried out on the basis of the optimum pre-form shape, and the effect of loading paths was deeply discussed on hydro-forming process. It is shown that the axial feeding within acceptable range can significantly improve the thickness distribution and forming accuracy. Finally, a well hydro-formed torsion beam is manufactured.

In order to resolve the problem that the polar zone is not deformed during hydro-forming of prolate ellipsoidal shell, a combined prolate ellipsoidal shell with double generating lines has been designed as the pre-form shell before hydro-forming. The distribution of the stress and variation of shell shape were analyzed by numerical simulation for hydro-forming of the combined prolate ellipsoidal shell, and the effect of structural design before hydro-forming was mainly discussed on the plastic deformation of the polar zone. It is shown that the polar zone is completely deformed towards to the design shape. The dividing line disappears with the increasing of internal pressure, and finally, every position along the longitudinal and latitudinal direction is a smooth arc. An experiment was conducted on hydro-forming of the new combined prolate ellipsoidal shell. The plastic deformation of the polar zone was deeply observed, and the variation of axis lengths and thickness was mainly measured in the experiment. It is shown that the polar zone is successfully deformed and the long axis has reached the design dimension during hydro-forming. Meanwhile, a sound prolate ellipsoidal shell has been obtained. It is proved that the needed prolate ellipsoidal shell can be formed by designing a reasonable pre-form shell.

In order to obtain a reasonable pre-form shell design for the needed sound ellipsoidal shell, a research has been conducted on variation of axis lengths during hydro-forming process of the combined ellipsoidal shell with double generating lines. Numerical simulation was carried out for parametric study of the pre-form shells with different structural parameters according to the Box-Behnken design method, and a mathematical response model between axis lengths and structural parameters was developed by multivariate quadratic regression analysis. Experiments were then carried out for hydro-forming process of the combined ellipsoidal shells with double generating lines. The deformation of the shell shape was separately reported, and the variation of axis lengths was recorded. Subsequently, comparative analysis of axis lengths between experimental data and predicted data coming from mathematical response model was deeply discussed. The comparison results show that the variation of axis lengths can be well predicted by the mathematical response model, which indicates that the needed ellipsoidal shell can be easily obtained by the optimization design of pre-form shell.

In order to avoid the wrinkling occurrence in the equatorial zone during hydro-forming of ellipsoidal shells with the axis length ratio exceeding 2 , a combined ellipsoidal shell with two axis length ratios has been designed as the pre-form shell before hydro-forming. The distribution of the latitudinal stress was analyzed by numerical simulation for hydro-forming of the combined ellipsoidal shells and the influence of the effective axis length ratio was discussed on the deformation. It is shown that there is latitudinal compressive stress in the equatorial zone at an early stage of deformation and then it becomes tensile stress with the internal pressure increasing, so that the wrinkling does not occur. An experiment was conducted on hydro-forming of the new combined ellipsoidal shells with the effective axis length ratio 1.47 and 1.65, respectively. The deformation of the shell shape, the variation of axis length, the roundness of the equatorial zone and thickness distributions were measured in the experiment. The wrinkling can be successfully avoided during hydro-forming and the sound ellipsoidal shells have been obtained. It is proved that hydro-forming of the combined ellipsoidal shell with two axis length ratios is reasonable and this new structure shell is suitable for manufacturing of the large-size ellipsoidal shells.

A hydro-pressing method was proposed to solve the problems in tube hydroforming process, such as too high pressure, nonuniform thickness distribution, and difficult forming of section corners. The process of hydro-pressing a tube seems like pressing of a solid bar. Theoretical analysis was performed, and the calculation formulas of hydro-pressing process parameters were given. Experimental research was conducted on hydro-pressing process of rectangular cross section with curved sides and bowtie cross-sectional components. The effects of supporting pressure, displacement of the pressing on section shape, and thickness distribution were investigated. The difference was compared between the hydro-pressing forming and the conventional mechanical pressing. It is demonstrated that the supporting pressure and pressing displacement are the essential parameters that influence cross-sectional shape and thickness. The dent defect disappears gradually as the supporting pressure increases and the thickness varies unobvious during hydro-pressing process of a rectangular cross section with curved sides. When the supporting pressure is 15 MPa, the maximum thinning of the rectangular cross section with curved sides is only 1.92 %. For a bowtie cross section, the required pressure is far less than that of conventional hydroforming for the same corner radius. Thickness distribution of section corner zone is more uniform than that formed by conventional hydroforming. Compared with conventional hydroforming, the hydro-pressing is a valid method to form the closed section tubular parts with the same perimeter and different cross-sectional shapes, which remarkably improves thickness distribution and reduces the forming pressure.

Friction stir welding (FSW), as a solid state joining technique, has emerged as an efficient method for manufacturing tailor-welded blanks to optimize weight or performance in the final component. As the basic design of lightweight frame structures in the automotive and aircraft industry is frequently based on tubular profiles, the joining strategies and forming technologies have to be developed accordingly. In the present study, FSW tube was produced by a novel processing sequence. The plastic deformation characteristics during hydroforming were experimentally and numerically investigated with two types of end condition. The hydroforming performance of the FSW tubes was mainly investigated by die-bulge forming with fixed ends, and the wrinkling behavior during hydroforming was analyzed by employing axial feed on the tube ends. It is found that hydroforming FSW tube is a new deal and does show a few peculiarities. The FSW tube exhibits a spiral weld and the basin-shaped nugget. Fine-grained structure is retained during tube forming. The thinning of the tube in axial direction shows M-shaped distribution during hydroforming. The severe thinning is observed at one quarter of the expansion zone from symmetry plane. In the hoop direction, the base material near the weld suffers severe thinning due to the high hoop and axial tensile stress. The thickness distribution greatly depends on the sequence of the contacting die and the variations of the curvature radius of the tube during hydroforming. Moreover, the weld shows an inhibitory effect for the generation of the wrinkles and decreases the number of the wrinkles as compared to the seamless tube during hydroforming. This effect is more obvious when the forming pressure is lower.

Structural and magnetic properties of rare-earth doped (Sr 2 − x Gd x )FeMoO 6 compounds ( x = 0, 0.05, 0.1, 0.13 and 0.15) have been investigated. All the compounds are of single phase and belong to the space group I4/m. Because of the small size of Gd 3+ ion (compared to that of Sr 2+ ion), obvious structural distortion is introduced in the compounds and imposes an important influence on the magnetic property of (Sr 2 − x Gd x )FeMoO 6 . The competing interaction between structural distortion and electron injection results in a non-monotonic evolution of the Curie temperature ( T C ): T C decreases firstly and then increases, with a minimum value at x ≈ 0.07. Contrary to the magnetic behavior of Eu 3+ ion in (SrEu)FeMoO 6 compound, the long-range ordered Gd 3+ moment is parallel to that of Fe 3+ ion at low temperature, and the contribution of the dopant to the saturation magnetization of (Sr 2 − x Gd x )FeMoO 6 is 6.75–7.15 μ B per Gd 3+ ion, which is comparable to the magnetic moment of a free Gd 3+ ion (7.0 μ B ). Above results indicate that although the rare earth elements exhibit similar chemical and optical character, their magnetic behavior in Sr 2 FeMoO 6 compound differs to a large degree.

Friction plays an important role in the corner filling behavior during hydro-forming of rectangular section. In order to study the variation in corner filling behavior with internal pressure under the condition of different coefficients of friction, Gurson–Tvergaard–Needleman ductile damage model was used to describe material deformation involving damage evolution. First, an experimental–numerical hybrid method was applied to determine the parameters of critical porosity and failure porosity in Gurson–Tvergaard–Needleman ductile damage model. Second, a model describing the deformation behavior was established, in which the deformation zone was divided into three parts: sticking zone, sliding zone and corner zone. Third, the effect of coefficient of friction on the corner filling process was studied through simulation and experiments. The results show that as the internal pressure increases, the sticking zone starts at certain pressure and increases rapidly until taking over the whole contact length. Sticking friction will lead to greater thinning, and bursting occurs rapidly at the transition zone. Furthermore, the increase in the coefficient of friction will lead to greater variation in thinning and corner radius. For µ = 0.05 in experiments, corner filling is acceptable without bursting, correspondingly the final internal pressure is 67 MPa.

As a new press, cylinder-crown integrated hydraulic press (CCIHP) is analyzed firstly in this paper. The hydraulic cylinder consists of a hemispherical shell, which also functions as a main proportion of press crown. Compared with the conventional hydraulic press which has a hydraulic cylinder mounted in the press crown, the structure and force distribution of CCIHP are significantly different. First, the section modulus of the hemispherical crown is much larger than that of the conventional rectangle crown because the hydraulic cylinder and press crown are manufactured into a solid part and have a higher geometry centroid. Therefore, the hemispherical crown has lower tensile bending stress and a higher safety factor from the strength point of view when the same bending moment is applied. Second, under the conditions of same value in terms of the allowable stress, internal pressure and internal radius, the wall thickness of hemispherical hydraulic cylinder could be much thinner than that of the conventional hydraulic cylinder. Both of the reasons mentioned above can result in a weight reduction of the press. Also, the cylinder and the press crown can be reinforced by each another, as a result, the material strength capacity is better utilized. As a prototype, the 6300 kN CCIHP with hemispherical hydraulic cylinder, which is the first one of this kind press designed and manufactured by Harbin Institute of Technology (HIT) is introduced in this paper. Finite element analysis for CCIHP has shown that both the stress and displacements on the press during the loading process are allowable, even if eccentric force is loaded. Finally the priority application range of CCIHP has also been proposed.

Due to economic and ecological reasons, the application of tailor-welded blanks of aluminum alloy has gained more and more attention in manufacturing lightweight structures for automotives and aircrafts. In the study, the research was aimed to highlight the influence of spinning on the formability of FSW tubes. The microstructural characteristics of the FSW tubes during spinning were studied by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The formability of the FSW tubes with different spinning reduction was assessed by hydraulic bulge test. It is found that the spinning process shows a grain refinement of the tube. The grains of the FSW tube decrease with increasing thickness reduction, and the effect of grain refinement is more obvious for the BM compared to that of the weld. The difference of grain size and precipitates between the weld and BM leads to an asymmetric W-type microhardness distribution after spinning. The higher thickness reduction of the tube, the more uniform distribution of grains and precipitates it shows, and consequently results in more significant increase of strength. As compared with the result of tensile test, the tube after spinning shows better formability when the stress state changes from uniaxial to biaxial stress state.

We study the evolution of magnetic excitations in the disordered two-dimensional antiferromagnet ${\mathrm{Sr}}_{2}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{4}$. The maximum energy of the magnetic excitation remains robust up to $x=0.77$, with a gap opening at low dopings and increasing to over 150 meV at $x=0.77$. At these higher Ru concentrations, the dispersive magnetic excitations in ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ are rendered essentially momentum independent. Up to a Ru concentration of $x=0.77$, both experiments and first-principles calculations show the Ir ${J}_{\text{eff}}=1/2$ state remains intact. The magnetic gap arises from the local interaction anisotropy in the proximity of the Ru disorder. Under the coherent potential approximation, we reproduce the experimental magnetic excitations using the disordered Heisenberg antiferromagnetic model with suppressed next-nearest-neighbor ferromagnetic coupling.

Subsequent spinning combined with post weld heat treatment (PWHT) was imposed to the friction-stir welding tube, and the effects of PWHT on the formability and microstructural stability of the FSW tubes were investigated in detail. The formability of tubes, evaluated by the hydraulic bulge test, is significantly improved after spinning and PWHT due to the grain refinement, removal of the thickness reduction and heterogeneous microstructure of the weld. Even abnormal grain growth occurs, the tubes still show a relatively high formability compared to the extruded tubes. The PWHT process plays key roles in controlling the size of precipitates and subgrains, and consequently dominates the microstructure stability that is correlated to the strain hardenability and formability of the tubes.

The effect of the microstructure heterogeneity on the tensile plastic deformation characteristic of friction stir welded (FSW) 2024 aluminum alloy was investigated for the potential applications on light weight design of vehicles. The microstructure characteristics of the FSW joints, such as the grain structure, dislocation density and the distribution of precipitation, were studied by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The tensile deformation characteristic of the FSW joints was examined using the automatic strain measuring system (ASAME) by mapping the global and local strain distribution, and then was analyzed by mechanics calculation. It is found that the tensile deformation of the FSW joints is highly heterogeneous leading to a significant decrease in global ductility. The FSW joints mainly contain two typical deformation zones, which show great effect on the regional inhomogeneous deformation. One is the nugget zone (NZ) with a region of 8 mm in width, and the other is part of the BM with a region of 10 mm in width. The BM of the joints is the weakest region where the strain localizes early and this localization extends until fracture with a strain over 30%, while the strain in the NZ is only 4%. Differences in regional strain of FSW joints, which are essentially controlled by grain structure, the distribution of precipitation and dislocation density, result in decrease on the overall mechanical properties.

A large-diameter thin-walled aluminum alloy tube was produced by friction stir welding combined with spinning, and the tube’s microstructure and mechanical properties were investigated. The microstructural heterogeneity of the friction stir welded joint is significantly improved by severe plastic deformation, which results in the generation of a fine-grained structure and uniform distribution of second-phase particles in the weld and base material. The weld region of the tube shows similar microstructure and mechanical properties to that in base material.

Finite element analysis (FEA) and experiment were conducted to reveal the reason of weld seam movement and its effects on strain state and thickness distribution during tailor-welded tube (TWT) hydrobulging with dissimilar thicknesses. It is indicated that weld seam movement happens during TWT hydrobulging, and the direction is from the thinner tube to the thicker tube, which induces nonuniform thickness distribution. The different strain states during the bulging process are the intrinsic feature of weld seam movement. Weld seam movement is aggravated by thickness difference between thinner and thicker tubes increase, but is insensitive to weld seam position. When the thickness ratio is bigger than 1.4, movement would concentratedly occur during the late period of the hydrobulging process. Such kind of deformation character can bring out local thickness thinning on a thinner tube, but on the contrary for a thicker tube, especially at the zone adjacent to weld seam. Consequently, sharp fluctuation of thickness distribution is brought out near the weld seam, which obviously cuts down fatigue life of the tube component.

Both experimental and simulation studies were run to investigate the effects of deformation sequence on stress and strain states and thickness distribution during tailor-welded tube hydroforming. The effects of geometrical boundary condition were also studied. Then, an approach to improve thickness uniformity was put forward. Both stress and strain histories indicate that the deformation states of thinner and thicker tubes were obviously different duo to the difference in thickness during tailor-welded tube hydroforming. These induce tensile strain concentrates to happen near weld seam on thinner tube, but compressive strain on thicker tube, which lead to strain mutation around weld seam on tailor-welded tube components. As result, bigger thinning takes place on thinner tube. The difference in thinning ratio between thinner and thicker tubes reaches about 6.6%. By deformation sequence optimization, thickness distribution uniformity can be improved obviously. When deformation sequence altered from thicker tube to thinner tube, the difference in thinning ratio between two segments can be decreased to 1.5%. At last, the effects of geometrical parameters of preform component were analyzed and the suitable parameters were given.

Post-weld annealing treatment (PWAT) process was developed to improve the plasticity of friction-stir-welded 2024 aluminum alloy. The effect of the PWAT on plastic deformation behavior and microstructure of the joints were studied using tensile test, the ASAME® automatic strain measuring system, and the electron backscattered diffraction (EBSD). It is found that the elongation of the as-welded joint can be improved by PWAT and increases with the decreasing PWAT temperature. The maximum elongation of the PWAT joints can reach up to 160% of that of the as-welded joint, and the joints exhibit no decrease in the tensile strength. The deformation inhomogeneity of the as-welded joint is significantly improved by large plastic strain occurring in the thermo-mechanically affected zone (TMAZ) when the PWAT temperature is lower than 250°. As the PWAT temperature increases, the deformation in the weld nugget is found to be more beneficial than that in the TMAZ for improving the plasticity of the joint. The high plasticity of the joint is attributed to the presence of the fine-equiaxed grains in the weld nugget during PWAT.

In the original version of this article, the formula found in Section 2.3 and Eq. 1 were presented incorrectly.

Both experimental and simulation studies were run to investigate the deformation uniformity of tailor-welded tube hydroforming with dissimilar thickness. The effects of weld-seam location and difference in thickness were analysed in detail. There are indications that obvious differences in deformation states appear between thinner and thicker tubes owing to poor deformation uniformity, which induces fluctuation in axial strain distribution, especially in the weld-seam zone nearby. Consequently, excessive thinning takes place on the thinner tube. Deformation uniformity improves as the length ratio increases or the thickness ratio decreases. However, it is more sensitive to the thickness ratio, and hence more effective for improving deformation uniformity by optimizing structure design.

Both experimental and simulation studies were run to investigate the deformation characteristics and influence of dissimilar thickness on hydro-bugling of tailor-welded tube. Both stress and strain histories obtained through finite element simulation indicate that the deformation of thicker tube lags behind the deformation of thinner tube all the way through the bulging process. Plastic deformation occurs first in the middle zone of the thinner tube and then extends to the thicker tube crossing the weld seam. In general, the expansion occurred in two segments with dissimilar thickness is nonuniform. But, the deformation compatibility increases with the length ratio. It is therefore concluded that the mechanism for improving the deformation compatibility is to induce the deformation in the thicker tube by enhancing the bulging pressure required for the deformation in the thinner tube by changing the stress state in the thinner tube and applying the work-hardening effect.

The tube hydroforming process for manufacturing the tubular part with large perimeter difference was studied by means of experiments and FE simulation. It is an asymmetrical one and the expansion ratio is 70 percent. The part is successfully hydroformed by applying the useful wrinkles to accumulate sufficient metal in the area with large expansion ratio. The thickness distribution is analyzed, and the maximum thinning ratio of the part is 21.6 percent. It is shown from the experiment and simulation results that the tubular part with large perimeter difference, long expansion area and asymmetrical shape can be obtained in one step, applying the useful wrinkles. Typical failure modes were analyzed.

The principle of the stretch reducing process is analyzed and three models of pass design are established. The simulations are done about variables, such as, stress, strain, the stretches between the stands, the size parameters of the steel tube, and the roll force parameters. According to its product catalogs the system can automatically divide the pass series, formulate the rolling table, and simulate the basic technological parameters in the stretch reducing process. All modules are integrated based on the developing environment of VB6. The system can draw simulation curves and pass pictures. Three kinds of database including the material database, pass design database, and product database are devised using Microsoft Access, which can be directly edited, corrected, and searched.

Shell hydroforming is a newly developed technology. Essentially, it is a die-less hydrobulging method, also named Integral Hydro-Bulge Forming (IHBF). Its basic principle of preforming before hydrobulging and its practical applications are introduced in this paper. Thickness and size change during the process, and numerical simulation, are also discussed.

The processes of precision forming of a flange for a large special vessel and a large pressure vessel are introduced in this paper. The common characters of these manufacturing processes are: (a) final precision machining was completed in the construction site with a multifunctional machine tool; (b) the flange was prepared from six or subparts in a conventional plant without joints; (c) precision assembly and welding of the subparts after transporting them to the construction site was performed to secure a solid ring before machining.

Rotary forging is an incremental forging process and is available to form various axisymmetrical parts from cylindrical billets. However, under certain conditions, a cylindrical billet is liable to be formed into a mushroom-shape after rotary forging, but not a drum shape in upsetting. A 3D rigid–plastic finite element method is used to simulate the rotary forging process to reveal the deformation mechanism of the mushroom shape workpiece. The stress, strain rate and strain distributions at different positions of the workpiece and at different times during the process are presented, and then the deformation zones are presented in detail for analyzing the deforming patterns. The reasons why the part with H0/D=0.5–1.0 (ratio of initial height to diameter) is formed into a mushroom shape are analyzed and it is concluded that these are non-uniform deformation under the effect of the eccentric loading and the different deforming degrees along the tangential direction at various heights of the workpiece. However, this kind of effect can be used to manufacture a part with a flange from a cylinder, instead of being regarded as a defect.

In this paper the authors try to extend the stress mechanics of tube hydroforming by combining the typical characteristics of stress states and yield equations of tube hydroforming with practical results. By determining how the stress state moves on the yield ellipse during the process, the characteristics of tube hydroforming are presented for the first time. The authors also discuss how the stress state effects the process and reach the conclusion that the control of tube hydroforming parameters is in fact the control of the stress state.

Five hollow components with complex cross-sections, including two automotive parts, were formed successfully in a hydroforming press with a maximum pressure of 400 MPa, under computer control. The thickness distributions are discussed in detail for every component, in particular for a chassis part. The materials of these five components cover aluminium alloy, stainless steel and mild steel and the application fields involve the aircraft, aerospace and automotive industries. Among these components, the maximum diameter of one hydroformed part is 161 mm and the maximum thickness is 4 mm. For parts with a greater expansion ratio, more than 50%, or low formability materials such as aluminium alloy, wrinkled tubular blanks can be used as preforms to form hollow components. By using this method, material is first accumulated in the expanding area by the formation of wrinkles, and then the wrinkles are flattened to shape the part by increasing the internal pressure in the calibration stage. The important thing point is to obtain “useful” wrinkles instead of “dead” wrinkles.

At the present time, hydroforming technology is used widely for forming lightweight or complicated components in the automotive industry and aerospace industry, etc. Recent developments and the character of hydroforming, especially sheet hydroforming and tube hydroforming, also known by the name of internal high pressure forming, are discussed in detail. Based on applications and by using liquid as a forming media, the state of the art and key technologies concerned with equipment, process control, simulation, etc. are explored in detail. Conclusions are drawn concerning possible future developments in hydroforming technology.

Large size vessels are widely used as LPG spherical tanks, elevated water towers, vacuum simulators for the space environment, landmarks and others. Prof. Z.R. Wang has supervised several engineering projects in which he has innovated manufacturing technologies. In this paper, some cases of large vessels manufactured by one of his inventions, integrated hydro-bulge forming, are described. Also the new large flange forming method and the new flexible reconfigurable discrete die for forming curved shell petals are introduced.

Numerical simulation by the finite-element method is one of the most powerful means for simulating sheet forming processes, including the possibility to predict the development of defects such as wrinkling. In this paper, numerical simulations of the integral hydroforming of shell products, the hydroforming process of tubular products and the viscous pressure forming of a superalloy corrugated part are reported. The simulations were conducted using the explicit finite-element code LS-DYNA and the code DEFORM.

Tube hydroforming is a process of manufacturing lightweight components, especially automotive parts. The typical failure modes such as folding back, wrinkling, buckling and fracture often occur due to the unreasonable selection of internal pressure and axial feeding. Most previous papers draw the conclusion that wrinkling is a failure mode. However, according to research carried out by the authors of this paper, not all wrinkles are defects. Accumulation of materials in main deformation areas through wrinkles is an alternative method for obtaining a perfect part. The key point is to obtain “useful” wrinkles instead of “dead” wrinkles. An investigation has been conducted on how to control the shape of the wrinkle waves and its effect on thickness distribution after hydroforming by using finite element simulation. To explore the effect of bending and unbending, a 2D simulation software, LS-DYNA2D, was used. It was found that the results from FEM can be used effectively of modelling of the main process parameters.