The electro-reduction of CO2 to produce energy sources has been considered as a visionary pathway with the help of renewable electricity, which can achieve carbon neutrality and mitigate global warming.
A CaCO3 coating with good anticorrosion and adhesion performance was fabricated via ultrasound-assisted chemical conversion on AZ41 magnesium alloy, with a water-bath treated coating as a control. The coating formed on AZ41 mainly consists of an outer CaCO3 layer and an inner (Ca, Mg)CO3 layer. Surface characterizations were carried out to obtain the morphology and the chemical composition, mechanical tests were also adopted to assess the hardness and the adhesion of the coating prepared. Afterwards, the long-term corrosion resistance was investigated via electrochemical methods in the chloride-containing Portland cement system. Results show that the ultrasound-assisted coating exhibits higher mechanical properties. In addition, the corrosion resistance of the ultrasound-assisted coating is also higher than that of the bare AZ41 alloy and the water-bath treated coating. This could be due to the formation of a much more compact CaCO3 coating on AZ41 Mg alloy, which is mainly benefit from the assistance of the ultrasound. Ultrasound accelerates the nucleation of CaCO3 crystals and assists the removal of hydrogen bubbles. Additionally, corrosion mechanism was suggested and discussed for the CaCO3 coating.
An anticorrosive CaCO3/MgO coating was obtained on AZ41 Mg alloy via rapid electrochemical deposition for the application of concrete formwork. Surface characterization was carried out to obtain the morphology and chemical composition of the coating. Afterwards, long-term anticorrosion performance was investigated via electrochemical methods in the chloride-containing Portland cement system. Results show that the electrochemical deposited coating consists of an outer CaCO3 layer and a compact inner MgO layer. Pre-immersion in the electrochemical deposition electrolyte contributed to the formation of a dense coating. The pretreatment plays an active role in the formation of an inner MgO layer, which significantly enhanced the binding between outer CaCO3 layer and Mg substrate. The electrochemical deposited CaCO3/MgO coating with pretreatment shows improved anticorrosion property than the coating without pretreatment, which could be ascribed to the formation of the dual-layer structure. Additionally, corrosion mechanism is suggested and discussed for the CaCO3/MgO coating.
Mg-Gd-Y-Zn-Zr alloy is an important lightweight material in the aerospace field. Wire arc additive manufacturing (WAAM) provides a new route to fabricate large Mg alloy components. Here, a Mg-8Gd-4Y–1Zn-0.5Zr (wt.%) alloy was fabricated using WAAM based on the cold metal transfer (CMT) process. Subsequently, a short-time solid solution + aging treatment was designed to tailor the microstructure. In the as-fabricated condition, the microstructure mainly consisted of fine α-Mg, network (Mg,Zn)3(Gd,Y) eutectic phase, and lamellar γ′ basal precipitate. After 500 °C-1 h short-time solid solution, the eutectic phase rapidly dissolved, the long-period stacking ordered (LPSO) phase formed, and the fine grain was maintained. Due to the good deformation capacity of the fine grains and the kinking deformation capacity of the LPSO phase, the ductility was significantly improved from 5.2 ± 0.4% to 15.5 ± 1.1%. After further 200 °C-64 h artificial aging, dense β′ prismatic precipitates formed. Thanks to the synergistic strengthening of the fine grains and β′ prismatic precipitates, a yield strength of 242 ± 4 MPa was achieved. However, the kinking deformation of the LPSO phase was inhibited, resulting in a drastic decrease of ductility to 6.1 ± 0.5%. Overall, the combination of strength and ductility of the CMT-based WAAM-processed Mg-Gd-Y-Zn-Zr alloy under an optimized heat treatment regime can be superior to those of the cast Mg-Gd-Y-Zn-Zr alloys with similar contents of Gd and Y elements. This work can guide further performance optimization for WAAM-processed Mg-Gd-Y-Zn-Zr alloys.
The poor anticorrosion property of magnesium alloys is one of main concerns prior to their various applications. In this study, an anticorrosive hydrogen phosphate coating was fabricated via the ultrasound-assisted chemical conversion treatment on AZ41 Mg alloy for concrete formwork. The coatings prepared by the conventional chemical conversion and hydrothermal treatment were also obtained as a comparison. Surface characterizations and electrochemical methods were carried out. Results show that the ultrasound-assisted coating obtained possesses a thickness more than 3 μm, which is thicker than the other two coatings. Moreover, the ultrasound-assisted coating presents a more homogeneous structure on the second phases, while the surface qualities of the other two coatings were significantly reduced due to the inhomogeneous CaHPO4·2H2O (DCPD) formed on the second phases in AZ41 Mg alloy. The ultrasound-assisted chemical conversion coating exhibits a good corrosion resistance even comparable to the hydrothermal coating. It exhibits a corrosion current density on the order of magnitude of 10-7 A·cm-2 even after the embedment of 96 h in the Portland cement (PC) system containing 3.5 wt.% NaCl.
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