Dingfei Zhang

In this work, we reported an unusual phenomenon of strain neutral layer (SNL) spreading in an as-rolled AZ31B magnesium alloy sheet during V-bending. The SNL on the middle symmetrical surface perpendicular to the transverse direction (TD) of the sheet extended to the compression region and was accompanied by a mound-like feature. However, the SNL on the side surface perpendicular to the TD was distributed with a parallel band feature. The underlying mechanism was revealed by the finite element (FE) analysis. The results indicate that the three-dimensional compressive stresses in the compression region of the bending samples were responsible for the above phenomenon. Moreover, the area of the SNL in the middle position gradually decreased as the bending test progressed. The findings in this study provide some new insights into the bending deformation behavior of magnesium alloy.

The layered metal oxide VOCl is a kind of promising electrode material for rechargeable batteries. It is the first time that the thermodynamic, electronic, and kinetic properties of lithiated and magnesiated VOCl were systematically investigated. The upper limit of Li and Mg topological intercalation into VOCl is x _Li = 1 and x _Mg = 0.5, respectively. Beyond the critical value, further lithiation and magnesiation will cause the phase evolution of layered VOCl. Upon lithiation, four discharge plateaus are observed at 2.10, 2.23, 1.62 and 1.23 V vs Li ⁺ /Li in the concentration range of 0 ≤ x _Li ≤ 1. Upon magnesiation, the average voltage reaches 1.10 V vs Mg ²⁺ /Mg in the concentration range of 0 ≤ x _Mg ≤ 0.25, which are consistent with the experimental values. The pair correlation function (PCF) diagrams display the formation of V metal at high concentration of x _Li and x _Mg , proving the occurrence of conversion reaction. The diffusion energy barriers of Li ions and Mg ions in VOCl are 0.22 and 0.72 eV, respectively, which are much lower than those of other intercalation materials. The layered VOCl bulk is a high-rate capability cathode material for lithium-ion battery. Based on the thermodynamic/kinetic properties and the AIMD simulation results, the electrochemical mechanism of layered VOCl is an intercalation-conversion reaction during the lithiated and magnesiated processes. The conversion-type cathodes have the potential to circumvent the sluggish solid-state Mg diffusion and improves the performance of Mg rechargeable batteries with high-energy density and high-rate capability.

Herein, the ZM61 alloys extruded at the extrusion ratios of 39 and 84 are named as ZM61‐39 alloy and ZM61‐84 alloy, respectively. The tensile mechanical properties and microstructure of both ZM61‐39 and ZM61‐84 alloys deformed at room temperature and different high strain rates (100, 500, and 1000 s⁻¹) along extrusion direction (ED) are investigated. The results show that, with the increase of strain rate, the strength of ZM61‐39 alloy changes a little, while the strength of ZM61‐84 alloy gradually increases. The fracture strain of both ZM61‐39 and ZM61‐84 alloys decreases as strain rate increases. The strength of ZM61‐39 and ZM61‐84 alloys shows different trends with increasing strain rates, which is mainly attributed to their different deformation mechanisms. The tension twinning‐basal slip dominates the deformation of ZM61‐39 alloy at high strain rates. And the nonbasal slip is the main deformation mechanism of ZM61‐84 alloy at high strain rates. In addition, ZM61‐39 alloy exhibits lower strength and better ductility than ZM61‐84 alloy at same high strain rates, which is strongly affected by the grain size.

Corrosion rates of ideal Mg alloys used for sealing tools in petroleum industry should be able to be altered to adapt to different downhole environments, and corresponding mechanisms of modified corrosion rates need to be clarified. In this study, annealing treatments were carried out at 400 or 450 °C for 2 h to tune the microstructures and corrosion rates of Mg-2Gd- x Cu ( x = 0, 0.5 and 1 wt.%). Microstructures were characterized by scanning electron microscope, X-ray diffractometer and electron backscatter diffraction while corrosion behaviors were investigated by immersion and electrochemical tests. The results showed that after annealing, the growth in the average second phase size and the average grain size, the weakened basal texture and the eliminated residual stress contributed to reduced corrosion rates. As a result, corrosion rates of Mg-2Gd-0.5Cu and Mg-2Gd-1Cu decreased obviously but were still higher than 30 mm·y ⁻¹ after annealing, the recommended minimum corrosion rates. It proved that a gradient of corrosion rates of Mg-Gd-Cu can be achieved through annealing treatment, which were beneficial to further application of Mg-Gd-Cu in the field of oil and gas exploitation.

To obtain alloys with both high degradability and plasticity used in the petroleum industry, 0.25, 0.5, 0.75 and 1.0 wt.% Cu were added into Mg-2Gd alloy. With Cu addition, finer grain size, precipitation of Mg ₂ Cu, and variations of crystal orientation were observed. Regardless of the good mechanical properties gained by alloying Cu, the degradation rate was obviously increased in this study. The corrosion rate and I _corr of Mg-2Gd were 13.0 ± 0.1 mm·y ⁻¹ and 1.04 × 10 ⁻⁴ A·cm ⁻² , respectively, while those value of Mg-2Gd-1Cu increased to 226.4 ± 6.1 mm·y ⁻¹ and 3.42 × 10 ⁻⁴ A·cm ⁻² , respectively. We confirmed by scanning Kelvin probe force microscopy and scanning electron microscope with electron backscatter diffraction detector that profuse second phases (mainly Mg ₂ Cu), refinement of grain size, and weakened rare earth texture contributed to the lower corrosion resistance.

Hot tears were frequently formed in Aluminum (Al) parts with complex structure. In this study, OM (optical microscope), SEM (scanning electron microscope), EDS (energy dispersive spectrometer), and FDM (finite difference method) were used to reveal the hot tears mechanisms in the casted AC4B Al engine. Shrinkage porosities with the size of 300–500 μm were found in casted specimens near the parts’ surface. Many cracked brittle Fe-bearing phase were also found in crack section. The secondary dendrite arm spacing observation in five typical positions showed that the cooling rate in position 5 was faster than that in position 1. The impropriety solidification sequence in position 5 and position 1 impeded the solidification feeding of position 1, and it might lead to casting defects or even casting cracks. Numerical simulation also showed that solidification sequence promoted casting defects, which was accordant with microstructure observation. Impurity may concentrate at position 5 during filling. It is concluded that large β-Fe intermetallics and improper solidification sequence together contributed to crack initiation in the engine.