Search Results (45)

Mg-Cu bimetallic materials have been widely studied because of their low density, good electrical conductivity, and excellent hydrogen storage properties. However, the interface bonding strength of Mg/Cu is low. In this study, we examined the effect of hot-dip tin coating (HDTC) with copper (Cu) on the interfacial metallurgical bonds between AZ91D Magnesium (Mg) alloy and Cu composite casting. A transition layer composed of Mg₂Cu and MgCu₂ intermetallic compounds (IMCs) formed at the interface of the AZ91D/HDTC-Cu composite casting. However, the transition layer was about 1 μm at the AZ91D/Cu interface, mainly comprising Mg(Al, Cu)₂ IMC. Both the AZ91D/Cu and AZ91D/HDTC-Cu interfaces exhibited many labyrinthine Mg(Al, Cu)₂ IMCs and layer-like Mg₂(Al, Cu) IMCs. Moreover, the interfacial shear strength of the AZ91D/Cu was changed from 12.6 MPa to 52.4 MPa due to the solid solution of Sn atom and the precipitation of Mg₂Sn IMC at the interface after HDTC treatment. Meanwhile, the shear fracture surfaces are characterized by brittle fractures. Full article

The presence of inherent micro-pores and micro-cracks in the micro-arc oxidation (MAO) film of Mg alloys is a key factor contributing to substrate corrosion. A composite film layer with high corrosion resistance was achieved through silanizing the micro-arc oxidation film. The corrosion performance of the MAO films treated with various silane coupling agents was assessed through morphological characterization and electrochemical tests. SEM graphs depicted that the silane film can effectively seal the defects existing in micro-arc oxidation film, and electrochemical tests indicated the significant corrosion resistance improvement of MAO film after silanization treatment. Full article

Magnesium (Mg) and its alloys offer promise for aerospace, railway, and 3D technology applications, yet their inherent limitations, including inadequate strength, pose challenges. Magnesium matrix composites, particularly with metallic reinforcements like titanium (Ti) and its alloys, present a viable solution. Therefore, this study investigates the impact of Ti6Al4V reinforcement on AZ31 magnesium alloy composites produced using pulse plasma sintering (PPS). Results show enhanced microhardness of the materials due to improved densification and microstructural refinement. However, Ti6Al4V addition decreased corrosion resistance, leading to strong microgalvanic corrosion and substrate dissolution. Understanding these effects is crucial for designing Mg-based materials for industries like petrochemicals, where degradation-resistant materials are vital for high-pressure environments. This research provides valuable insights into developing Mg-Ti6Al4V composites with tailored properties for diverse industrial applications, highlighting the importance of considering corrosion behavior in material design. Further investigation is warranted to establish predictive correlations between Ti6Al4V content and corrosion rate for optimizing composite performance. Full article

With the development of computational thermodynamics, it is possible to design a material based on its simulated microstructure and properties before practical operations. In order to improve the surface properties of AZ91D magnesium alloy, Jmatpro was used in this study to design an alloy system with in situ TiC+AlTi_3-reinforced aluminum coatings. The Gibbs free energy, hardness, and phase diagrams of aluminum coatings with different ratios of Ti to B₄C were simulated. According to the simulation results, TiB₂, TiC, Al₃Ti_DO₂₂, and Al₄C₃ were formed in the coating while TiB₂, TiC, Al₃Ti_DO₂₂, Al₄C₃, and Al₃Mg₂ were formed in the transition zone between the base metal and the coating. Based on the simulation results, different amounts of Ti were used with B₄C (the ratios were 3:1, 4:1, 5:1, and 6:1) to fabricate TiC+Al₃Ti reinforced aluminum coatings on AZ91D magnesium alloy via laser cladding. The microstructure and phase composition of the coating were studied using scanning electron microscopy (SEM) incorporated with energy- dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results indicated that intermetallic phases, such as AlTi₃(C, N)_0.6, AlMg, Al₃Mg₂, Al₃Ti, and TiC were formed in the coatings. As the Ti content increased, the content of Al₃Ti increased and the content of TiC decreased in the coatings, which is consistent with the simulation results. The average hardness of the coatings was approximately four to five times that of the magnesium alloy substrate, and the corrosion current density of the coatings was around 2.5 × 10⁻⁶, which is two orders of magnitude lower than that of AZ91D magnesium alloy. Full article

In this study, near-liquidus squeeze casting AZ91D alloy was used to prepare differential support, and the microstructure and mechanical behavior under different applied pressure were investigated. Under the preset temperature, speed, and other process parameters, the effect of applied pressure on the microstructure and properties of formed parts was analyzed, and relevant mechanism was also discussed. The results showed that the ultimate tensile strength (UTS) and elongation (EL) of differential support can be improved by controlling real-time precision of the forming pressure. The dislocation density in the primary phase increased obviously with the pressure increasing from 80 MPa to 170 MPa, and even tangles appeared. When the applied pressure increased from 80 MPa to 140 MPa, the α-Mg grains were gradually refined, and the microstructure changed from rosette to globular shape. With increasing the applied pressure to 170 MPa, the grain could not be further refined. Similarly, its UTS and EL gradually increased with the applied pressure increasing from 80 MPa to 140 MPa. With increasing to 170 MPa, the UTS tended to be constant, but the EL gradually decreased. In other words, the UTS (229.2 MPa) and EL (3.43%) of the alloy reached the maximum when the applied pressure was 140 MPa, and the comprehensive mechanical properties were the best. Full article

The modified nano-CeO₂/Zn–Mn phosphate composite coating was deposited on AZ91D magnesium alloy by chemical conversion to enhance its densification and corrosion resistance. The growth mechanism and corrosion resistance of the composite coating is clarified by adding different concentrations of ZnO and a certain amount of nano-CeO₂ into the phosphate-plating solution. XRD and EDS show that the composite membrane is mainly composed of MgO, Mg(OH)₂, Mn₃(PO₄)₂·5H₂0, Zn, Zn₃(PO₄)₂·4H₂O and CeO₂. Among them, AZ91D magnesium alloy matrix presents dispersed granule, clustered and petal-shaped under the action of different concentrations of ZnO. Under the optimum ZnO concentration, after adding nano-CeO₂, dense grains appear, and cracks and pores in the riverbed are obviously reduced. Compared with single-layer phosphate coating, the performance of composite coating is significantly improved. The results show that the obvious double-layer structure is observed by SEM, and the thickness of the coating is about 48 μm. The LCSM shows that the surface roughness of composite coating is moderate. EIS shows that when the fitting impedance is 8050.43 Ω and PH = 3, the dropping time of copper sulfate in the composite coating is 58.6 s, which is better than that in the single-layer coating. The Tafel polarization fitting curve shows that the corrosion current density of the composite coating is obviously lower than that of the single coating, the corrosion current density is decreased from 1.86 × 10⁻⁶ A/cm² to 9.538 × 10⁻⁷ A/cm², and the corrosion resistance is obviously improved. Full article

Atmospheric pressure plasma (AP) treatment, using an open-air jet of ionized CO_2, N₂, or air, was applied to AZ91D Mg alloy surfaces to investigate its effects on primer coating adhesion and corrosion resistance. The CO₂ and air AP treatments formed an O- and C-rich surface layer (Mg-O-C) consisting of agglomerated nanoparticles and pits with a depth of a few microns and increasing the surface roughness by 6–8 times compared with the reference 600 grit-finished surface. Then, three commercial primers, zinc phosphate (ZnP), chromate-containing epoxy, and MIL23377, were applied on the treated surfaces to evaluate the corrosion resistance associated with the coating adhesion. Microscopic analysis demonstrated stronger interlocking between the primer layer and the nano-/microrough Mg-O-C surface compared to the untreated (600 grit-finished) surfaces, indicating improved coating adhesion and corrosion resistance. Crosscut tests of the MIL23377 primer on the CO₂ and air AP-treated surfaces showed the highest level of adhesion, ASTM class 5B. Salt spray corrosion tests showed that after 8 days of exposure, the primer coatings on air AP-treated surfaces had corrosion areas that were more than four times smaller than that of the 600 grit-finished surface. The N₂ AP treatment showed similar adhesion enhancement. The preliminary operation expenses for AP treatment using CO₂, N₂, and air were estimated at USD 30.62, USD 35.45, and USD 29.75 (from an air cylinder)/USD 0.66 (from an air compressor) per m², respectively. Full article

The Mg-Al-Zn-Ca system has demonstrated excellent flame resistance and mechanical properties in the as-cast condition. However, the potential of these alloys to be heat-treated, e.g., by aging, as well as the influence of the initial microstructure on the precipitation kinetics, is yet to be comprehensively explored. Ultrasound treatment was applied during the solidification of an AZ91D-1.5%Ca alloy to promote microstructure refinement. Samples from treated and non-treated ingots were subjected to solution treatment at 415 °C for 480 min, followed by aging at 175 °C for up to 4920 min. The results showed that the ultrasound-treated material could reach the peak-age condition in a shorter period than the non-treated one, suggesting accelerated precipitation kinetics and, thus, enhanced aging response. However, the tensile properties showed a decrease in the peak age compared to the as-cast condition, probably due to the formation of precipitates at the grain boundaries that promote the formation of microcracks and intergranular early fracture. This research shows that tailoring the material’s as-cast microstructure may positively affect its aging response, shortening the heat treatment duration, thereby making the process less expensive and more sustainable. Full article

SiC_p/AZ91D magnesium matrix composites with 30% SiC_p were successfully prepared by pulsed current melting in this work. Then, the influences of the pulse current on the microstructure, phase composition, and heterogeneous nucleation of the experimental materials were analyzed in detail. The results show that the grain size of both the solidification matrix structure and SiC reinforcement are refined by pulse current treatment, and the refining effect is gradually more obvious with an increase in the pulse current peak value. Moreover, the pulse current reduces the chemical potential of the reaction between SiC_p and Mg matrix, thus promoting the reaction between SiC_p and the alloy melt and stimulating the formation of Al₄C₃ along the grain boundaries. Furthermore, Al₄C₃ and MgO, as heterogeneous nucleation substrates, can induce heterogeneous nucleation and refine the solidification matrix structure. Finally, when increasing the peak value of the pulse current, the repulsive force between the particles increases while the agglomeration phenomenon is suppressed, which results in the dispersed distribution of SiC reinforcements. Full article

Magnesium alloys are perspective materials for use in transportation, aerospace and medical industries, mainly because of their good load-to-weight ratio, biocompatibility and biodegradability. For the effective production of magnesium components by the laser powder bed fusion (LPBF) process, the process parameters with verified mechanical properties need to be determined. In this paper, we prepared bulk samples with a high relative density of AZ91D magnesium alloy. Tensile tests were then performed on LPBF samples to evaluate the mechanical properties. Our results show that the bulk samples achieved a relative density >99%, in multiple planes over the full sample height, while the mechanical properties reached values of Y_S = 181 MPa, UTS = 305 MPa and A_5.65 = 5.2%. The analysis by scanning electron microscope revealed fine β-Mg₁₇Al₁₂ particles in the microstructure, which have a positive effect on the mechanical properties. The chemical composition of magnesium alloy AZ91D changed slightly during processing by LPBF due to the evaporation of the Mg content. However, the resulting composition still corresponds to the range specified by the ASTM standard for the AZ91D alloy. Full article

Porous structures of magnesium alloys are promising bioimplants due to their biocompatibility and biodegradability. However, their degradation is too rapid compared to tissue regeneration and does not allow a progressive metal substitution with the new biological tissue. Moreover, rapid degradation is connected to an accelerated ion release, hydrogen development, and pH increase, which are often causes of tissue inflammation. In the present research, a natural organic coating based on tannic acid was obtained on Mg AZ91 porous structures without toxic reagents. Mg AZ91 porous structures have been prepared by the innovative combination of 3D printing and investment casting, allowing fully customized objects to be produced. Bare and coated samples were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), fluorescence microscopy, Fourier transformed infrared spectroscopy (FTIR), tape adhesion test, Folin–Ciocalteu, and degradation tests. Different parameters (solvent, dipping time) were compared to optimize the coating process. The optimized coating was uniform on the outer and inner surfaces of the porous structures and significantly reduced the material degradation rate and pH increase in physiological conditions (phosphate-buffered saline—PBS). Full article

The effect of Y₂O₃ addition on the microstructure and properties of the laser cladded Al-Si alloy coating on the surface of AZ91D magnesium alloy was investigated in this study. The experimental results showed that the Al-Si + Y₂O₃ cladding layers contained α-Mg, Mg₂Si, Al₄MgY and a small amount of Al₁₂Mg₁₇ phases. The coarse dendrites, reticulated eutectic structures and massive phases in the coatings tended to be refined and gradually uniformly distributed with the increased amount of Y₂O₃. The introduction of Y₂O₃ into the cladding layer favored the improvement of microhardness and wear resistance due to the grain refinement strengthening and dispersion strengthening. The addition of Y₂O₃ also promoted the reduction of localized corrosion sites and made the corrosion surface smoother, implying that the corrosion resistance of the Y₂O₃-modified coatings was better than that of the unmodified cladding layer. Full article

The synthesis of Eu³⁺-doped MgAl oxide coatings containing MgO and MgAl₂O₄ was accomplished through plasma electrolytic oxidation of AZ31 magnesium alloy in aluminate electrolyte with the addition of Eu₂O₃ particles in various concentrations. Their morphological, structural, and above all, photoluminescent (PL) and photocatalytic activity (PA) were thoroughly investigated. PL emission spectra of MgAl oxide coatings feature characteristic emission peaks, which are ascribed to f–f transitions of Eu³⁺ ions from excited level ⁵D₀ to lower levels ⁷F_J. The charge transfer state of Eu³⁺ or direct excitation of the Eu³⁺ ground state ⁷F₀ into higher levels of the 4f-manifold are both attributed to the PL peaks that appear in the excitation PL spectra of the obtained coatings. The fact that the transition ⁵D₀ → ⁷F₂ (electrical dipole transition) in Eu³⁺-doped MgAl oxide coatings is considerably stronger than the transition ⁵D₀ → ⁷F₁ (magnetic dipole transition) indicates that Eu³⁺ ions occupied sites with non-inversion symmetry. Because of oxygen vacancy formation, the Eu³⁺-doped MgAl oxide coatings had a higher PA in the degradation of methyl orange than the pure MgAl oxide coating. The highest PA was found in Eu³⁺-doped MgAl oxide coating formed in an aluminate electrolyte with 4 g/L of Eu₂O₃ particles. The PA, morphology, and phase of Eu³⁺-doped MgAl oxide coatings did not change after several consecutive runs, indicating outstanding stability of these photocatalysts. Full article

Magnesium and its alloys are widely used in many areas because of their light weight, excellent dimensional stability, and high strength-to-weight ratio. However, the material exhibits poor wear and corrosion resistance, which limits its use. Plasma electrolytic oxidation (PEO) is an effective surface modification method for producing ceramic oxide layers on Mg and their alloys. The influence of the additions of sodium tetrafluoroborate (NaBF₄) and sodium fluoride (NaF) into alkaline-silicate electrolyte on the properties of the conversion layers formed in the magnesium AZ91D alloy has been investigated. Surface morphology and chemical composition were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The anticorrosive properties of the layers were evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods in simulated body fluid (SBF). The presence of NaBF₄ or NaF in the electrolyte increases the corrosion resistance of the protective layer. However, the best anticorrosive properties show the layers obtained in the presence of NaBF₄. This is probably caused by the incorporation of boron and fluorine in the form of Mg (BF₄)₂ mainly in the barrier layer. Full article

Micro-arc oxidation (MAO) coatings were obtained from an AZ91D magnesium alloy at different oxidation times (5, 10, 15, and 20 min), using a zirconium salt electrolyte system, with (NH₄)₂ZrF₆ as the main salt. The morphology of the coatings was studied using a scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). Energy dispersive spectrometry (EDS), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to determine the type of element and the composition of its phase. The potentiodynamic polarization curve (PDP) was applied to illustrate the corrosion resistance of the coatings. We found the coatings had minor porosity and the best compactness when the MAO treatment time was 10 min. The coatings mainly comprised MgO, ZrO₂, MgF₂, and Zr₃O₂F₈ phases and amorphous magnesium phosphate. Among the MAO coatings prepared in this experiment, the 10 min coating had the lowest corrosion current density (I_corr), and the I_corr was 4.864 × 10⁻⁸ A/cm², which was three orders of magnitude lower than the uncoated AZ91D magnesium alloy. Full article