Xiao-Song Wang

The deformation of parts with complex shapes is under a tensile and shear stress state. The deformation characteristics of materials under the tensile and shear stress state are beneficial for improving the prediction accuracy of the deformation of parts with complex shapes. A loading method of circumferential tension-axial shear of thin-walled tubes using two semi-circle mandrels and one specially designed tubular specimen is proposed in this paper. An experimental device was developed according to this method using servo electric cylinders. A thin-walled 5052 aluminum tube was tested and the strain path of the center point of the deformation zone was analyzed. This loading method can be used to investigate the characteristics of tubular material under the tensile and shear stress state.

Owing to orange-peel defects, the industrial application of light alloy structural members is significantly restricted. In this study, a quasi-in situ axial tensile experiment was conducted on a 6063-T4 aluminum alloy sample. The surface morphology and microstructure evolution of the tagged area were scanned simultaneously using laser scanning confocal microscopy and electron backscattered diffraction, and the surface roughening behavior of the polycrystal aluminum alloy surface, caused by deformation, was quantitatively analyzed. As the concave–convex features at the surface appear in pairs with increasing global strain, the width of the concave features increases, whereas that of the convex features decreases gradually, resulting in the initially increasing surface roughness, which subsequently remains unchanged. During the stretching process, the small-sized grains in the 37~102 μm range show weak strain localization and the highest coordination of deformation. The deformation mode of medium-sized grains in the 114–270 μm range tends to grain deflection, and others tend to slip.

TiBw/TA15 (TA15 alloy reinforced by TiB whiskers) composites with network microstructures were successfully prepared by current-assisted sintering at 1100 °C for 10 min. The influence of the sintering parameters on the microstructures of obtained composites was investigated. The sintering temperature was the main factor affecting the average aspect ratio of TiBw, and the average diameter of TiBw could be controlled for various sintering conditions. Yield strength, ultimate compressive strength, and plastic strain at ambient temperature are 1172.5 MPa, 1818.4 MPa, and 22.4% for the TiBw/TA15 composites, respectively. Moreover, yield strength of the composites at 600 °C is 616.3 MPa, which is 26.1% higher than that of the TA15 titanium alloy. The effect of the TiBw on the microstructure evolution for the alloy matrix was discussed in detail. The strengthening mechanism of the TiBw/TA15 composites with network microstructure was attributed to the microstructure modification induced by TiBw, load bearing effect, and dislocation strengthening effect of the TiBw.

Severe surface roughening during the hydroforming of aluminum alloy parts can produce surface defects that severely restrict their application in the automobile and aerospace industry. To understand the relation between strain, grain size and surface roughness under biaxial stress conditions, hydro-bulging tests of aluminum alloy tubes were carried out, and the tubes with different grain sizes were prepared by a spinning and annealing process. The surface roughness was measured by a laser scanning confocal microscope to evaluate the surface roughening macroscopical behavior, and the corresponding microstructures were observed using electron back-scattered diffraction (EBSD) to reveal the roughening microscopic behavior. The results obtained show that the surface roughness increased with both strain and grain size under biaxial stress. No surface defects were observed on the surface when the grain size was less than 105 μm if the strain was less than 18%, or when the grain size was between 130 and 175 μm if the strain was less than 15.88% and 7.15%, respectively. The surface roughening microscopic behavior was identified as an inhomogeneous grain size distribution, which became more pronounced with increasing grain size and resulted in greater local deformation. Concentrated grain orientation also results in severe inhomogeneous deformation during plastics deformation, and serious surface roughening.

Control and use of wrinkles is a challenge in tube hydroforming because wrinkle was always considered as one of the defects of tubes from the traditional view. In this paper, a dedicated experimental setup was designed and manufactured, using which the investigation of wrinkling behavior coupled with internal and external pressure can be realized. The effect of internal or external pressure on 5A02 aluminum alloy tubes and 0Cr18Ni9 stainless steel tubes were all investigated using this setup. It was found that the number and shape of wrinkles are strongly dependent on the internal or external pressure. More important is that the geometrical configuration of wrinkles can be perfectly characterized using the Gauss function rather than the sine function adopted in the published literature. In addition, the fitted Gauss functions for every wrinkle were integrated in order to compare their area with the corresponding area of die cavity, so as to obtain the appropriate process parameters for the useful wrinkle, which can be formed in advance and then flatted in the calibration stage.