Transactions of Nonferrous Metals Society of China最新文献

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al− 2Nb−2Cr−0.15B alloy at 1160−1220 °C for 30 min. The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature, interfacial microstructure and joint strength were emphatically investigated. Results show that the TiAl joints brazed at 1160 and 1180 °C possess three interfacial layers and mainly consist of α₂-Ti₃Al, τ₃-Al₃NiTi₂ and Ti₂Ni, but the brazing seams are no longer layered and Ti₂Ni is completely replaced by the uniformly distributed τ₃-Al₃NiTi₂ at 1200 and 1220 °C due to the destruction of α₂-Ti₃Al barrier layer. This transformation at 1200 °C obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa. Notably, the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.

The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses, including electrical conductivity, mechanical properties, local corrosion properties, and slow strain rate tensile stress corrosion tests. Microstructure characterization techniques such as metallographic microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were also employed. The results indicate that the tensile strength of the alloy produced by T6I6 aging is similar to that produced by T6I4 aging, and it even exceeds 700 MPa. Furthermore, the yield strength increases by 52.7 MPa, reaching 654.8 MPa after T6I6 aging treatment. The maximum depths of intergranular corrosion (IGC) and exfoliation corrosion (EXCO) decrease from 116.3 and 468.5 µm to 89.5 and 324.3 µm, respectively. The stress corrosion factor also decreases from 2.1% to 1.6%. These findings suggest that the alloy treated with T6I6 aging exhibits both high strength and excellent stress corrosion cracking resistance. Similarly, when the alloy is treated with T6I4, T6I6 and T6I7 aging, the sizes of grain boundary precipitates (GBPs) are found to be 5.2, 18.4, and 32.8 nm, respectively. The sizes of matrix precipitates are 4.8, 5.7 and 15.7 nm, respectively. The atomic fractions of Zn in GBPs are 9.92 at.%, 8.23 at.% and 6.87 at.%, respectively, while the atomic fractions of Mg are 12.66 at.%, 8.43 at.% and 7.00 at.%, respectively. Additionally, the atomic fractions of Cu are 1.83 at.%, 2.47 at.% and 3.41 at.%, respectively.

The coupling effects of electrical pulse, temperature, strain rate, and strain on the flow behavior and plasticity of 5182-O aluminum alloy were investigated and characterized. The isothermal tensile test and electrically-assisted isothermal tensile test were performed at the same temperature, and three typical models were further embedded in ABAQUS/Explicit for numerical simulation to illustrate the electroplastic effect. The results show that electric pulse reduces the deformation resistance but enhances the elongation greatly. The calibration accuracy of the proposed modified Lim−Huh model for highly nonlinear and coupled dynamic hardening behavior is not much improved compared to the modified Kocks−Mecking model. Moreover, the artificial neural network model is very suitable to describe the macromechenical response of materials under the coupling effect of different variables.

A 3D elastic-plastic FE model for simulating the force controlled stretch-bending process of double-cavity aluminum profile was established using hybrid explicit−implicit solvent method. Considering the computational accuracy and efficiency, the optimal choices of numerical parameters and algorithms in FE modelling were determined. The formation mechanisms of cross-section distortion and springback were revealed. The effects of pre-stretching, post-stretching, friction, and the addition of internal fillers on forming quality were investigated. The results show that the stress state of profile in stretch-bending is uniaxial with only a circumferential stress. The stress distribution along the length direction of profile is non-uniform and the maximum tensile stress is located at a certain distance away from the center of profile. As aluminum profile is gradually attached to bending die, the distribution characteristic of cross-section distortion along the length direction of profile changes from V-shape to W-shape. After unloading the forming tools, cross-section distortion decreases obviously due to the stress relaxation, with a maximum distortion difference of 13% before and after unloading. As pre-stretching and post-stretching forces increase, cross-section distortion increases gradually, while springback first decreases and then remains unchanged. With increasing friction between bending die and profile, cross-section distortion slightly decreases, while springback increases. Cross-section distortion decreases by 83% with adding PVC fillers into the cavities of profile, while springback increases by 192.2%.