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In this study, Mg-13.2Gd-4.3Ni alloys containing continuous bulk-shaped long-period stacking ordered (LPSO), lamellar LPSO, and a small amount of eutectic phase were prepared, and the evolution of microstructure at different extrusion temperatures and its influence on mechanical and degradation properties as well as corrosion mechanism were investigated. Preheating before extrusion can effectively promote the precipitation of lamellar LPSO in matrix. EX400 with higher volume fraction of non-DRXed grains exhibited higher strength, which was mainly due to strong texture, high dislocation density, and high volume fraction of lamellar LPSO. The EX420 with higher volume fraction of DRXed grains showed higher degradation rate, which was mainly due to the higher density of grain boundary. The EX400 exhibited excellent comprehensive properties with tensile yield strength (TYS) of 334 MPa, ultimate tensile strength (UTS) of 484 MPa and elongation (EL) of 7.4%, ultimate compressive strength (UCS) of 638 MPa and compressive yield strength (CYS) of 443 MPa, degradation rate of 86.1 mg/cm2/h at 93 °C in 3 wt.% KCl solution. [ABSTRACT FROM AUTHOR]

A systematic investigation was undertaken to explore the influence of microstructure evolution in the as-cast, heat-treated, and as-extruded on the corrosion properties of a high-performance Mg-5.6Dy-3.1Ni alloy, which includes two intermediate phases. It was found that degradation rate of both as-cast and heat treated alloys primarily depended on the distribution of the LPSO and Mg 6 Ni intermetallic phases. For the as-extruded alloy, the degradation rate depended on both the distribution of the LPSO and Mg 6 Ni phases and the grain refinement of the matrix. Compared with as-cast alloy, the corrosion barrier was formed and inhibited the corrosion propagation after heat treatment. This was attributed to the network distribution of the LPSO phase, coupled with a uniform distribution of Mg 6 Ni phase. After extrusion, After extrusion, the streamlined distribution of the stripped LPSO phase. This led to a reduced corrosion barrier in the extrusion direction (ED) sample, resulting in a higher degradation rate compared to the transverse direction (TD) sample. Furthermore, the LPSO phase and grain refinement after extrusion provided a denser corrosion product film to retard the degradation rate in the TD sample. A high mechanical properties Mg-5.6Dy-3.1Ni alloy with different degradation rates in the as-cast, heat-treated, and along the extrusion direction and in the transverse direction was developed. • Developed a high strength Mg-Dy-Ni alloy with different corrosion rates by different process conditions. • The mechanism of microstructure evolution on the degradation rate of high-strength Mg-Dy-Ni alloy was elucidated. • The study alloy meet the fracturing tools with high strength and different degradation time demand. [ABSTRACT FROM AUTHOR]

• Three kinds of release agents were attempted on the surface of AZ41 Mg alloy. • Corrosion resistance of AZ41 Mg alloy embedded in Portland cement paste was studied. • Oil-based release agent coated Mg alloy presents the best corrosion resistance. Anticorrosion performance of AZ41 Mg alloy coated with three different kinds of release agents was investigated embedded in Portland cement (PC) paste containing 0.6 M NaCl. Surface characterizations were employed to obtain the surface information after coated with release agents before and after embedment. Meanwhile, electrochemical methods were adopted to assess the corrosion resistance embedded in PC paste. Results demonstrated that water-based release agent led to the corrosion of Mg alloy while the oil-based release agent not only protected the Mg alloy but also exhibited the best demolding effect. Oxide films can be generated on the surface of Mg alloy after coated with release agents. The thin film after applying the water-based release agent was magnesium/aluminium oxide and hydroxide with some talcum (3MgO·4SiO 2 ·H 2 O) particles. Additionally, thin films on the surface of Mg alloy after coated with emulsified and oil-based release agents were magnesium/aluminium oxide and hydroxide. [ABSTRACT FROM AUTHOR]

The Mg 95.34 Gd 2.66 Cu 2 alloy containing profuse solute segregation stacking faults (SFs) phase was prepared through solution treatment and furnace cooling, and its effect on corrosion behavior and corrosion mechanism were investigated. After heat treatment, the microstructure distribution of continuous bulk-shaped Mg 5 (GdCu) phase at grain boundaries and profuse solute segregation SFs phases in the matrix was realized. Compared with the as-cast alloy without SFs phase, the corrosion morphology exhibited that the galvanic corrosion expanded rapidly along the length direction of SFs phase after heat treatment. The Mg 95.34 Gd 2.66 Cu 2 alloy heat treated at 420 °C exhibited the optimal comprehensive performance, with the ultimate compressive strength (UCS), compressive yield strength (CYS) and degradation rate of 437 MPa, 291 MPa, 56.5 mg/(cm2·h), respectively. And the degradation rate increased by 40% compared with the as-cast alloy. • The profuse SFs were prepared in Mg 95.34 Gd 2.66 Cu 2 alloys by heat treatment. • SFs increased the volume fraction of the cathode phase and improved the degradation rate. • A rapid corrosion microstructure distribution model was proposed. [ABSTRACT FROM AUTHOR]

In order to enhance the corrosion resistance of the AZ41 Mg alloy used as concrete formwork, a bilayer CaCO 3 /MgO coating was fabricated on the surface of AZ41 Mg alloy with addition of Ca-EDTA in the chemical conversion solutions. Effect of different Ca-EDTA concentrations on the surface morphology of as-prepared CaCO 3 /MgO coating and corrosion resistance in simulated concrete pore solutions with 3.5 wt% NaCl were investigated. SEM, XPS and XRD were combined to investigate the morphology and composition of the coatings. Electrochemical methods and immersion tests were used to assess the anticorrosion performance of the as-prepared coatings. Results show that an integrated bilayer CaCO 3 /MgO coating can be prepared on AZ41 Mg alloy by the addition of Ca-EDTA. Electrochemical tests reveal that the CaCO 3 /MgO coating prepared at 0.01 M Ca-EDTA possesses the best corrosion resistance at varying concentrations of Ca-EDTA. Ca-EDTA accelerates the release of Mg2+ and further affects both nucleation and growth of CaCO 3 particles. Appropriate addition of Ca-EDTA can simultaneously preserve the stability of CaCO 3 and enhance coating density. • A bilayer CaCO 3 /MgO coating via ultrasound-assisted chemical conversion improve the corrosion resistance of AZ41 Mg alloy. • Addition of disodium calcium of ethylenediamine tetra-acetic acid (Ca-EDTA) can improve the density of CaCO 3 particles. • The CaCO 3 /MgO coating prepared at 0.01 M Ca-EDTA possesses the best corrosion resistance. • Both stable components and a dense structure maybe key factors for a coating to possess outstanding corrosion resistance. [ABSTRACT FROM AUTHOR]

The effects of the high content of erbium (Er) addition (9.5–17 wt%) and short-time low-temperature heat treatment on the microstructure evolution, corrosion behaviors and mechanism of Mg-xEr-1.6Ni alloys have been investigated. After heat treatment, the corrosion rate for various Er content alloys increased by 15.1–338.8% in comparison to as-cast alloys, which was mainly related to the formation of Er-rich phases and the increase the density of laminar γ′ phase. These phases increase the galvanic coupling pairs and provide more corrosion propagation paths, reducing the Er content in the Mg matrix and weakening the corrosion barrier. • Corrosion mechanism of Mg-xEr-1.6Ni alloy with different Er content was revealed. • Corrosion rate increased by 15.1%− 338.8% after low-temperature heat treatment. • Increased corrosion rate is due to formation of Er-rich phase and increased γ′ phase. • This work provides foundation for designing high-degradation Mg alloy. [ABSTRACT FROM AUTHOR]

The microstructure and corrosion behaviors of Mg-Gd–Ni alloys with various long period stacking ordered (LPSO) phase volume fraction and heat treatments were investigated. Compared with as-cast alloys, the corrosion rates increased significantly after heat treatment, and increased with increasing volume fraction of LPSO phase, which may be due to the transformation of continuous bulk reticular LPSO phase to discontinuous rod-like and the precipitation of the lamellar 14 H LPSO phase, changing the corrosion propagation paths and providing more galvanic corrosion points for alloy with high LPSO phase volume fraction, resulting in corrosion rate of MgGd3Ni3 alloy increased significantly by 58.1%. • The corrosion mechanism of Mg-Gd-Ni alloys by change of LPSO phase volume fraction and heat treatment were clarified. • The change of corrosion propagation paths and precipitation of lamellar LPSO phase accelerates the corrosion of the alloys. • Compared toas-cast alloys, the corrosion rates of MgGd 3 Ni 3 alloy increased significantly by 58.1% after heat treatment. [ABSTRACT FROM AUTHOR]

The passive behaviour of new alloy corrosion-resistant steel Cr10Mo1 and plain carbon steel (as a comparison) in simulating concrete pore solutions of different pH (ranging from 13.5 to 9.0) under open circuit potential conditions, was evaluated by various electrochemical techniques: potentiodynamic polarization, capacitance measurements and electrochemical impedance spectroscopy. The chemical composition and structure of passive films were investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The electrochemical responses of passive films show that Cr10Mo1 steel has an increasing passivity with pH decreasing while carbon steel dose conversely, revealing carbonation does no negative effect on passivation of the corrosion-resistant steel. SIMS reveals that the passive film on the corrosion-resistant steel presents a bilayer structure: an outer layer mainly consisting of Fe oxides and hydroxides, and an inner layer enriched in Cr species, while only a Fe-concentrated layer for carbon steel. According to the XPS analysis results, as the pH decreases, more stable and protective Cr oxides are enriched in the film on Cr10Mo1 steel while Fe oxides gradually decompose. Higher content of Cr oxides in the film layer provides Cr10Mo1 corrosion-resistant steel more excellent passivity at lower pH. [ABSTRACT FROM AUTHOR]

In order to develop new Mg alloys for fracturing tools, Mg-Gd-Cu alloys containing profuse solute segregated stacking faults (SFs) were prepared by appropriate heat treatments and the effect of SFs on corrosion behavior of the alloys was investigated. It was found that the presence of SFs greatly changed corrosion behavior of the Mg-Gd-Cu alloys. Specifically, the alloys containing SFs presented higher initial corrosion rate due to the increased volume fraction of the cathodic phase associated with the SFs; while the rapid formation ability as well as uniform and complete distribution of corrosion films resulted in a lower average degradation rate. • The profuse solute segregated stacking faults were prepared in Mg-Gd-Cu alloys by heat treatment. • The presence of stacking faults greatly changed corrosion behavior of the Mg-Gd-Cu alloys. • Heat-treated alloys exhibited higher initial corrosion rates due to the increased volume fraction of the cathodic phase associated with the stacking faults. • The rapid formation ability as well as uniform and complete distribution of corrosion product films of heat-treated alloy resulted in a lower average corrosion rate. [ABSTRACT FROM AUTHOR]