Search

Solid-state welding offers distinct advantages for joining reactive materials, such as magnesium (Mg) and its alloys. This study investigates the effect of linear friction welding (LFW) on the microstructure and mechanical properties of cast AZ91 (Mg–9Al–1Zn) and AZ91–2Ca alloys, which (to the best knowledge of the authors) has not been reported in the literature. Using the same set of LFW process parameters, similar alloy joints—namely, AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca—were manufactured and found to exhibit integral bonding at the interface without defects, such as porosity, inclusions, and/or cracking. Microstructural examination of the AZ91/AZ91 joint revealed dissolution of the Al-rich second phase in the weld zone, while the Mn containing phases remained and were refined. In the AZ91–2Ca/AZ91–2Ca joint, the weld zone retained Ca- and Mn-rich phases, which were also refined due to the LFW process. In both joint types, extensive recrystallization occurred during LFW, as evidenced by the refinement of the grains from ~1000 µm in the base materials to roughly 2–6 µm in the weld zone. These microstructural changes in the AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca joints increased the hardness in the weld zone by 32%. The use of digital image correlation for strain mapping along the sample gage length during tensile testing revealed that the local strains were about 50% lower in the weld zone relative to the AZ91 and AZ91–2Ca base materials. This points to the higher strength of the weld zone in the AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca joints due to the fine grain size, second phase refinement, and strong basal texture. Final fracture during tensile loading of both joints occurred in the base materials.

The corrosion performance of the AZ91 and AZ91 + 2%Ca (AZX912) magnesium alloys joined using linear friction welding was investigated. For similar and dissimilar metal combinations—namely AZ91/AZ91, AZX912/AZX912, and AZ91/AZX912, the performance was evaluated by mass loss analysis and the scanning vibrating electrode technique in 1 wt% NaCl solution. Galvanic behavior between AZ91 and AZX912 was examined by potentiostatic polarization and galvanic current measurements. Approximately 0.3–0.6 mm thick seamless weld zones were generated in all of the welds, which did not show any appreciable changes in the surface profiles acquired after the corrosion test. The corrosion-induced mass loss rate of the AZ91/AZX912 dissimilar weld was 10% higher than those of the AZ91/AZ91 and AZX912/AZX912 similar welds. The galvanic test indicated that AZ91 and AZX912 were the anodic and cathodic regions, respectively, with a difference in the corrosion potential of 20–30 mV. The corrosion of the AZ91/AZX912 weld was presumed to proceed via a macro-galvanic cell between the base alloys, whereas the weld acted as a bridge and did not influence the corrosion.

Tensile properties, formability and thermal conductivity of Mg-3Zn-0.5Ca-0.5Al-xMn (x: 0.1–1.5 in wt%) sheet alloys with different Mn contents were investigated. Benefitting from dense Al-Mn nanoscale spherical precipitates, yield strength was significantly enhanced by 39 MPa with increasing the Mn content from 0.1 wt% to 1 wt%. In the meanwhile, excellent formability was maintained with Erichsen values larger than 8 mm. Further increasing the Mn content to 1.5 wt% did not contribute to strengthening due to the formation of coarse β-Mn particles. In spite of larger additive amount, thermal conductivity improved for the 1 wt% Mn added alloy compared to the 0.1 wt% Mn added alloy due to the increased amount of Al-Mn nanoscale spherical precipitates, which reduced a content of Al solute atoms. High strength (average yield strength: 180 MPa), high formability (Erichsen value: 8.5 mm) and high thermal conductivity (133 W/(m K)) were simultaneously achieved in the 1 wt% Mn added alloy.

In this study, the discharge performance of Mg-6 wt% Al alloy anodes with varying Ca and Zn contents was evaluated by electrochemical studies and surface analyses. The results indicated that the cell voltage and anode efficiencies changed according to the alloy compositions and discharge currents. The 6 wt%Al-1wt%Zn-1wt%Ca (AZX611) alloy was discovered to exhibit the highest cell voltage of 0.678 V and anode efficiency of 64% at the discharge current of 10 mA cm−2. Although the calculated charge corresponding to the mass loss of AZX611 was equal to the sum of the calculated charge stemming from the captured H2 and the discharge current, the other alloys yielded smaller values. The discharge products of these alloys were analyzed by X-ray diffraction to locate the peaks related to metallic Mg species. The electrochemical impedance spectroscopy analysis of the AZX611 alloy, conducted under the discharged state using a proposed equivalent circuit, revealed a close relationship between the resistance in the high frequency loop and the anode efficiency.

This paper describes the sintering behavior of combustion-synthesized (Y, Ca)-α-SiAlON powders when using spark plasma sintering (SPS) technology. The effects of sintering temperature, heating rate, and holding time on the densification behavior, α→β phase transformation, and Vickers hardness were investigated in detail. Fully dense Y-α-Si 12−( m + n ) Al m + n O n N 16− n ( m =1.2, n =0.6, Y-α-SiAlON) and Ca-α-Si 12−( m + n ) Al m + n O n N 16− n ( m =1.0, n =0.5, Ca-α-SiAlON) were obtained during sintering for 10 min at final temperatures as low as 1400 °C and 1500 °C, respectively. X-ray diffraction results showed that more than 50 mass% of α-phase transformed to the β-phase for Y-α-SiAlON after SPS, whereas no obvious α→β phase transformation was observed for Ca-α-SiAlON, even after sintering at a high temperature of 1600 °C. A maximum Vickers hardness of 18.56 GPa and 19.95 GPa was reached for Y-α-SiAlON and Ca-α-SiAlON, respectively.

The time variation of galvanic corrosion that occurred in an AZX611 magnesium/A6N01 aluminum alloy in differently concentrated NaCl solutions was evaluated by galvanic potential/current measurements and the Scanning Vibrating Electrode Technique (SVET). The weight loss and surface profile of alloy samples after the test were measured to quantify the degree of galvanic corrosion. The galvanic current showed a maximum at the initial stage and then decreased with time. Higher concentrations of NaCl resulted in higher currents, and the decay proceeded at a slower rate. The weight loss measurement revealed that galvanic corrosion damaged not only AZX611 but also A6N01 due to the surface alkalization caused by the cathode reaction. SVET detected numerous local anodes on the AZX611 surface, which gradually disappeared and were replaced with passive areas. As the NaCl concentration increased, local anodes appeared at the joint, which agrees with the results of previous studies. For the A6N01 counterpart, the entire surface was corroded regardless of NaCl concentration. The analysis of the surface profile supported the SVET results. It was concluded that the galvanic corrosion of the AZX611/A6N01 joint was controlled by the depassivation behavior of the AZX611 anode, in which the NaCl concentration was critical.

High-quality Y- and Ca-α/β-SiAlON and α-SiAlON ceramics were synthesized via salt-assisted combustion synthesis from Si, Al, and metal oxide (Y2O3 and CaO) with the addition of NaCl and MgCl2 under a nitrogen pressure of 1 MPa. NaCl and MgCl2 were employed as they act as excellent diluents that effectively absorb the reaction heat through melting and evaporation. We found that the type of metal chlorides employed significantly affected the α/β ratio and the morphology of the product, with the use of NaCl affording high α/β ratios and equiaxed morphologies, while the use of MgCl2 resulting in low α/β ratios and elongated grains. The results of this work suggest that high-purity α/β-SiAlON composite products of intended α/β ratios can be successfully fabricated by controlling the initial metal chloride content.

Reaction characteristics of combustion synthesis (CS) of β-SiAlON powders in a horizontal CS chamber were compared by including two types of additives (β-SiAlON and NaCl) in Si, SiO2, and Al powder raw materials. The results showed that the reaction characteristics were influenced by the additives, which exerted a strong effect on the reaction rate and the morphology of the products. At the respective maximum combustion temperatures, a relatively slow conversion rate, with a reacted fraction (η) of 58.7%, was achieved with the addition of 12 mass% NaCl to the raw materials, whereas the addition of 45 mass% β-SiAlON powders afforded η = 88%. The NaCl additive yielded rod-like crystals, which were well developed by a long after-burn time. However, self-sintering occurred in the presence of β-SiAlON powders. The results indicate that some degree of control over the conversion rate of the reaction and the microstructures of the product can be achieved by varying the type of additives.

A facile salt-assisted combustion synthesis of β-SiAlON and systematic characterization of the endothermic effects of addition of KCl, MgCl 2 , and CaCl 2 were investigated under a nitrogen pressure of 1 MPa. Single-phase products containing crystals with different shapes were obtained. The results indicated that the metal chlorides act as perfect diluents that effectively absorb the reaction heat via their melting and evaporation, which occur in the same temperature ranges as the two stages of the exothermic processes. In addition, the products exhibited different morphologies when the type or amount of metal chlorides was changed. The results of this work suggest that single-phase β-SiAlON could be fabricated with the intended morphology by simply adding different kinds of metal chlorides.

In this work, fine powders of spinel-type LiMn 2 O 4 as cathode materials for lithium ion batteries (LIBs) were produced by a facile solution combustion synthesis using glycine as fuel and metal nitrates as oxidizers. Single phase of LiMn 2 O 4 products were successfully prepared by SCS with a subsequent calcination treatment at 600–1000 °C. The structure and morphology of the powders were studied in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were characterized by galvanostatic charge–discharge cycling and cyclic voltammetry. The crystallinity, morphology, and size of the products were greatly influenced by the calcination temperature. The sample calcined at 900 °C had good crystallinity and particle sizes between 500 and 1000 nm. It showed the best performance with an initial discharge capacity of 115.6 mAh g −1 and a capacity retention of 93% after 50 cycles at a 1 C rate. In comparison, the LiMn 2 O 4 sample prepared by the solid-state reaction showed a lower capacity of around 80 mAh g −1 .

In this work, nanoparticles of LaMO3 (M = Fe, Co, Mn) perovskite oxide catalysts were produced by facile solution combustion synthesis with glycine as the fuel and metal nitrates as the oxidizers. The electrocatalytic activities of the catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were evaluated using a three-electrode half-cell design and a full rechargeable Zn-air battery with a 6 M KOH electrolyte. Comprehensive study of combustion synthesis and characterization of synthesized products showed that LaFeO3 had been successfully prepared in a single step of combustion synthesis, while the synthesis of LaCoO3 and LaMnO3 required an extra calcination step. The effects of the glycine/nitrate ratio and the calcination temperature and duration on the particle size and crystallinity of the final products were evaluated. Electrochemical characterization showed that LaMnO3 exhibited the best catalytic activity for both ORR and OER during the initial discharge-charge cycles, especially for the ORR corresponding to the discharge of the Zn-air battery. The order of activity is as follows: LaMnO3 > LaCoO3 > LaFeO3 > CB (carbon black). However, cycling performance measurements showed that the LaMnO3 catalyzed air electrode degraded very quickly, whereas the LaCoO3 catalyzed electrode exhibited the best rechargeability and stability.

A novel method of producing submicron-size β-SiAlON powders by combustion synthesis using NaCl as a diluent was proposed. The combustion synthesis was carried out with the raw materials Si, SiO2, and Al powders, and varying amounts of NaCl under a nitrogen pressure of 1 MPa. Phase compositions and particle morphologies of the synthesized powders were analyzed. The results revealed that as the z-values increased, the amount of NaCl needed to complete the reaction increased, which in turn decreased the particle size of the product. With small z-values, single-phase products were obtained; however, with large z-values, NaCl and unreacted Si remained in the products due to the large amount of liquid phase. NaCl acted not only as a diluent by absorbing the heat generated by the reaction but also as a diffusion barrier between β-SiAlON particles, which greatly limited the growth of β-SiAlON crystals.

Significance Single-phase β-SiAlON particles with submicron size were prepared via combustion synthesis (CS) using natural kaolin, Si, and Al as raw materials under a nitrogen atmosphere of 1 MPa. Kaolin could not only act as the raw material to provide the source of oxygen, but also act as the diluent to reduce the reaction temperature by eliminating the structural water during reaction process.

A process for the industrial production of magnesium hydride (MgH 2 ) based on a thermal equilibrium method and its application to portable hydrogen sources is proposed. Mg powders and tablets compressed with mechanically ground Mg ribbons were successfully hydrogenated in a 50-kg-batch furnace. The resultant MgH 2 showed a hydrogen yield of around 96% with good reproducibility. The compression ratio of Mg tablets was found to be an important factor in the hydrogenation yield. A hydrolysis technique using citric acid as an additive was employed to generate hydrogen under 373 K. Increasing the concentration of citric acid and the temperature accelerated the hydrolysis reactivity. A hydrogen reactor utilizing hydraulic head pressure was developed. It generated hydrogen continuously for 1 h at a flow rate of 100 ml min −1 with hydrolysis of 5 g of tablet-form MgH 2 . The conversion yield was around 70%, regardless of the flow rate.

Glow Discharge Optical Emission Spectroscopy (GD-OES) was applied to analyze the surface structure of injection-molded AZ91D magnesium alloy products. The thickness of surface layer containing mold lubricant is approximately 300 nm. H and C elements are good indicators for monitoring the presence of mold lubricant. A chemical cleaning system based on acid etching, desmutting and neutralizing steps can provide the magnesium surface free from mold lubricant.

Laser melting can be used to alter the surface of alloys and produce a fine microstructure, usually improving corrosion resistance. In the present work, a pulsed Nd:YAG laser was used to melt and rapidly quench the surface of die cast AZ91D and AM60B magnesium alloys with the objective of improving the corrosion resistance in salt-water (NaCl) solution. The corrosion of AZ91D and AM60B was not significantly reduced by laser melting even though the microstructure of both alloys was refined but a close examination of corroded surfaces gave indications about some corrosion enhancing factors. The physical aspect of corroded surfaces and the microstructure of laser melted specimens are presented along with the results of corrosion tests.

The corrosion behavior of nitrogen ion (N2+)-implanted AZ91D magnesium alloy (UNS M11916) in 5 wt% sodium chloride (NaCl) solution was investigated using weight-loss measurement and electrochemical techniques. Ion implantation improved corrosion resistance at doses > 1 × 1016 ions/cm2 (6.5 × 1016 ions/in.2). At doses of 5 × 1016 ions/cm2 (3.27 × 1017 ions/in.2), the mean corrosion rate and maximum pitting depth reached minimums. Impedance spectra drew a capacitive semicircle at 2 × 1016 or 5 × 1016 ions/cm2 (1.3 × 1017 ions/in.2 or 3.2 × 1017 ions/in.2). Additional inductive loops were observed in the lower frequency of untreated or implanted specimens outside this range. The presence of the inductive loop was discussed in terms of corrosion morphology, particularly in terms of the occurrence of pitting corrosion. Monitoring polarization resistance (Rp) was shown to be useful in evaluating effects of ion implantation.

The growth rate of magnesium casting production in North America has averaged 16.6 percent per year over the last ten years.1−3 The fastest growing application for magnesium is the high-pressure die casting for automotive components, which represents approximately 70–80% of the magnesium casting shipments in recent years. This paper presents the latest developments in magnesium alloys, product design, casting technology, surface finishing, and magnesium-matrix composites. Current and future automotive applications of magnesium castings are also discussed.