Facile Fabrication and Properties of Super-hydrophobic MgAl-LDH Films With Excellent Corrosion Resistance on AZ31 Magnesium Alloy

A super-hydrophobic anti-corrosion film was facilely prepared via in situ growth of layered double hydroxides (LDHs) on the etched AZ31 magnesium alloy and then modification by 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane (PFOTMS) in this work. The morphology, structure, composition, surface roughness and water contact angles (WCA), and the anti-corrosion performance of the samples were investigated. The results revealed that the micro/nano hierarchical surface morphology of the films was composed of island structures obtained after chemical etching and MgAl-LDH nanowalls grown in situ. The best hydrophobicity (CA = 163°) was obtained on the MgAl-LDHs with the maximum surface roughness. Additionally, the potentiodynamic polarization, electrochemical impedance spectroscopy, and immersion test indicated that the super-hydrophobic LDH films provided better corrosion resistance to AZ31 magnesium alloy due to the double-protection derived from the LDHs and super-hydrophobic properties. Furthermore, the contact angle could be kept at above 140° after dipped in 3.5 wt% NaCl solution for 6 days.

Temperature Dependency on the Microscopic Mechanism in the Normal Direction of Wrought AZ31 Sheet under Dynamic Compressive Behavior

In order to analyze the competitive relationship of different deformation mechanisms in wrought AZ31 magnesium alloy, the dynamic compressive experiments were conducted by a Split Hopkinson Pressure Bar (SHPB) apparatus and a resistance-heated furnace in the range of temperature between 20 and 350 °C at the strain rate of 1000 s−1. With the help of Electron Backscattered Diffraction (EBSD) observation, theoretical calculated Schmid Factor (SF), Critical Resolved Shear Stress (CRSS), and critical equivalent stress (σ0.2), the dynamic compressive deformation behavior and corresponding mechanism of wrought AZ31 magnesium alloy along the normal direction (ND) were revealed in the current study. The results demonstrate that the c-axis of grains are gradually reoriented parallel to the normal direction of wrought AZ31-ND sheet with the temperature increasing, except the dynamic recrystallization (DRX) mechanism was activated or grains grew up. The non-basal slip and 101¯2 tension twinning are respectively the predominant deformation mechanisms at lower temperatures (≤250 °C) and higher temperatures (≥250 °C). The predominant type of DRX mechanism of wrought AZ31-ND sheet is rotational dynamic recrystallization (RDRX), which is regarded as an obstacle for the kernel misorientation concentration region enhancement.

Numerical study on the plastic deformation behavior of AZ31 magnesium alloy under different loading conditions

Based on the stress characteristics of the instantaneous cross-section deformation of the wall reducing section during the cold rolling of two-roll Pilger pipes, the rectangular samples with 0° and 90° to the extrusion direction (ED) were cut from the extruded AZ31 magnesium alloy bar for 3% pre-deformation test to simulate its stress state equivalently. The sample was then cut from the pre-deformed sample by wire cutting for secondary compression, and the sample that is not pre-deformed is selected. The mechanical behavior and texture evolution of AZ31 magnesium alloy under different loading conditions were respectively studied by EBSD experiment and VPSC simulation. Results show that the true stress–strain curve and texture evolution characteristics of AZ31 magnesium alloy during the secondary compression process are in good agreement with the prediction of the VPSC model. The secondary compression behavior can be effectively explained by the relative activity of the deformation modes. The pre-deformation in the ∥ED (⊥ED) direction is conducive to the shift of the pole density of the {0001} basal surface texture to the positive and negative directions of the ED (TD). The pre-deformed sample exhibits a higher yield strength than the non-pre-deformed sample in the same loading direction. The high ductility of magnesium alloys can be achieved by activating pyramidal 〈c + a〉 slippage.