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• Polymer-Portland cementitious coatings with autogenerated oxide film were prepared on Mg alloy. • PC-based coatings enhance corrosion resistance of Mg alloy by three orders of magnitude. • Addition of dolomite and metakaolin enhances resistance of PC-based coating. • Autogenerated oxide film of coated Mg alloy plays a dominant role in anticorrosion. • Adsorption of MoO 4 2– further enhances the quality of autogenerated oxide film. A simple one-step anticorrosion Portland cement (PC)-based coating with an autogenerated oxide film on the surface of Mg alloy was successfully prepared in this study. The anticorrosion of coated Mg alloys was assessed by several electrochemical methods including open circuit potential, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization. The morphology and composition of PC-based coatings were characterized via scanning electron microscopy and X-ray diffraction. The composition of the autogenerated oxide film was analyzed via X-ray photoelectron spectroscopy. Results show that the PC-based coatings can significantly enhance the corrosion resistance of AZ41 Mg alloy due to the synergetic effect of PC-based coating and autogenerated oxide film. Particularly, the quality of oxide film plays a dominant role in determining anticorrosion of Mg alloy. Furthermore, the addition of metakaolin and dolomite enhances the resistance of PC-based coating and meanwhile, MoO 4 2– ions from PC-based coating can adsorb in the oxide film, improving the quality of the oxide film. [Display omitted] [ABSTRACT FROM AUTHOR]

• A high strength and high corrosion rate Mg-Er-Ni alloy was designed and fabricated by regulating the LPSO and γ′ phases. • Mg-13.5Er-4Ni alloy with outstanding mechanical strength (UTS: 514 MPa) and corrosion properties (142.5 mg cm−2 h−1). • The corrosion and mechanical mechanisms are elucidated for high strength and high corrosion rate Mg-Er-Ni alloy. As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered (LPSO) phase and density of lamellar γ′ phase were prepared, and the microstructure, mechanical, and degradation properties were investigated. Coupling the bulk LPSO phase and the lamellar γ′ phase, and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ′ phase, a synergistic increase in strength and degradation rate can be achieved. On the one hand, the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ′ phase, which provide more galvanic corrosion. Moreover, high densities of the lamellar γ′ phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized (DRXed) grains during the hot extrusion. On the other hand, the ultimate tensile strength (UTS) and tensile yield strength (TYS) of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa, respectively, which was mainly attributed to grain boundary and texture strengthening, bulk LPSO phase and lamellar γ′ phase strengthening. Overall, Mg-14Er-4Ni alloy, which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ′ phase, realized a synergistic enhancement of strength and degradation rate. The UTS, TYS, and degradation rate of Mg-14Er-4Ni were 514 MPa, 358 MPa, and 142.5 mg cm–2 h–1 (3 wt% KCl solution at 93 ℃), respectively. This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments. [Display omitted] [ABSTRACT FROM AUTHOR]

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−2even after the embedment of 96 h in the Portland cement (PC) system containing 3.5 wt% NaCl.

An anticorrosive CaCO3/MgO coating was obtained on AZ41 Mg alloy via rapid electrochemical deposition for the application of concrete formwork. Surface characterizations were 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 CaCO3layer 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 CaCO3layer 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.

AbstractUltra-high-performance concrete (UHPC) has attracted much attention in civil engineering. However, the high deadweight of UHPC limits its application. To reduce the density of UHPC, this study developed an ultra-high-performance lightweight concrete (UHPLC) by combining the use of shale ceramic sand and nano-materials, according to the modified Andreasen and Andersen (MAA) model. Taking advantage of nanotechnology, graphene oxide (GO) was utilized to improve the mechanical performance of UHPLC, and the effects of GO on the workability, mechanical properties, and microstructure of UHPLC were systematically investigated. It was found that: 1) UHPLC with an apparent density of 2022 ∼ 2114 kg/m³ was prepared according to the MAA model; 2) Owing to the addition of GO, the flexural strength, compressive strength, and elastic modulus of UHPLC increased by 6.3 ∼ 22.4%, 7.6 ∼ 16.7%, and 4.1 ∼ 13.0%, respectively; 3) Considering the effects of GO on the mechanical properties and microstructure of UHPLC, the optimal content of GO was 0.06%.

The Mg–Er–Ni alloy with comparable strength and solubility was prepared by controlling the Ni content. The mechanical properties and corrosion mechanism of alloys with long-period stacking ordered (LPSO) phase, as well as those with both LPSO and γʹ phases, were investigated and clarified. This study focused on investigating the underlying reasons for the high mechanical strength and fast corrosion rate of the Mg–13Er–3Ni alloy with LPSO and γʹ phases. The highest corrosion rate of the Mg–13Er–3Ni (wt.%) alloy is not only associated with the high volume fraction of the LPSO phase, which provides a larger zone for the corrosion cathode rather than forming a corrosion barrier, but also linked to the introduction of the γʹ phase that forms new sites for galvanic corrosion and avoids the formation the Er2O3corrosion product film with corrosion-resistant. Moreover, The high mechanical properties of Mg–13Er–3Ni alloy are mainly attributed to the texture strengthening, dislocation strengthening and the second phase reinforcement that were caused by high volume fraction of LPSO phase and the precipitation of lamellar γʹ phase in Mg matrix. Generally, Compared to the Mg–13Er-1.5Ni (wt.%) alloy, the corrosion rates and mechanical strength of Mg–13Er–3Ni (wt.%) alloy were increased significantly by 302.8% and 50.3%, respectively, by coupling the LPSO and γʹ phases. Its ultimate tensile strength of 445 MPa and corrosion rare of 128.5 mg cm−2 h−1, which provides a new high strength and rapid corrosion Mg alloy materials for fracturing tools application.

The effects of Er and Ni content on the microstructure evolution, corrosion mechanism of Mg–Er–Ni alloys with different orientations were investigated. With the increase of Er and Ni content, the corrosion rate of extrusion direction (ED) increases, while transverse direction (TD) is reversed, which may be due to the distinct corrosion mechanism in different orientations, where ED and TD exhibit soluble and corrosion-resistant mechanism, respectively. Moreover, high content second phase alloy with a large deformation grain fraction and low levels second phase alloy with fully recrystallized grains have larger and smaller corrosion rate differences in ED and TD, respectively.

Laser powder bed fusion (LPBF) of AlMgScZr alloys have a combination of high strength and good ductility, which may apply to damage-tolerant structures. However, there have been only limited studies on the toughness performance of this promising alloy system. In the present work, the impact toughness of an LPBF-processed AlMgScZr alloy, which is critical for the application that involves high-strain-rate loading, was systematically investigated using instrumented Charpy impact testing. The results demonstrated that the AB(as-built)-LPBF-processed AlMgScZr alloy had a good combination of yield strength and impact toughness (338 ± 3 MPa, 27.47 ± 1.04 J), which were about 2 and 4 times those of the AC(as-cast)-processed AlMgScZr alloy (160 ± 1 MPa, 6.21 ± 0.66 J). However, post-aging treatment greatly deteriorated the impact toughness. On one hand, the strain-hardening capability of the LPBF-processed AlMgScZr alloy was reduced after post-aging; on the other hand, the coplanar slip associated with the L12superlattice structure of the secondary Al3(Sc,Zr) phase promoted the intergranular brittle fracture. This resulted in the remarkable strength-impact toughness conflict in the AA(as-aged)-LPBF-processed AlMgScZr alloy (512 ± 2 MPa, 4.27 ± 0.09 J). This study not only provides valuable insights into the dynamic fracture resistance of the LPBF-processed AlMgScZr alloys but also sheds light on the importance of choosing whether to post-age the LPBF-processed AlMgScZr alloy based on service loading conditions.