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This study explores the synthesis of AZ61 alloy composite powders with Co-Ni additives using high-energy ball milling (HEBM). The powders are extensively characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to analyze their morphology, composition, structure, and bonding. The hydrogen storage capacity of the powders is measured using a Sievert's-type system revealing diverse capacities. For AZ61 alloy with Ni additive (2 µm), it absorbs 90% of the capacity in 410 s, showing an activation energy of 91.46 kJmol−1 and displays Mg 2 NiH 4 as an intermediate. On the other hand, AZ61 alloy with Co additive requires 576 s to absorb 90% of the capacity, showing an activation energy of 117.23 kJmol−1 and Mg 2 CoH 5 as an intermediate. When a mixture of Ni and Co is added to AZ61 alloy, it achieves 90% capacity absorption in 300 s. In the absence of additives, AZ61 alloy (15 µm) reaches 90% capacity absorption in 1600 s. The incorporation of additives significantly reduces the activation energy. A correlation between longer absorption times and larger activation energies provides valuable insights into the storage kinetics and activation energy associated with the hydrogen absorption/desorption process. [Display omitted] • The addition of Ni, Co, and a mixture of Ni and Co to the AZ61 alloy enhances its hydrogen storage capacity compared to the alloy without additives. • The hydrogen storage capacities of the AZ61 alloy with Ni, Co, and Ni-Co additives were measured to be 4.5 wt%, 5.316 wt%, and 5.14 wt%, respectively. • The presence of specific reaction intermediates, such as Mg 2 NiH 4 and Mg 2 CoH 5 , was confirmed through XRD patterns, indicating their role in the hydrogen absorption process and promoting reversibility and cycle stability. • The activation energy for hydrogen absorption in the AZ61 alloy with Co additive was found to be 117.23 kJ/mol while that of Ni was 91.46 kJ/mol. • Kinetics to achieve 90% capacity: AZ61 alloy with Ni additive requiring 410 s, the alloy with Co additive requiring 576 s, the alloy with Ni and Co mixture requiring 300 s, and the alloy without additives requiring 1600 s. These results highlight the influence of additive composition on the kinetics of hydrogen absorption. [ABSTRACT FROM AUTHOR]

In this work, a practical numerical model with few parameters was proposed for the prediction of environmental hydrogen embrittlement. The proposed method adopts hydrogen enhanced plasticity-based mechanism in a fracture strain model to describe hydrogen embrittlement. Fracture toughness degradation of three commercial steels SA372J70, AISI4130 and X80 in high pressure hydrogen environment were investigated. Firstly, governing equations for hydrogen distribution and material damage evolution was established. Hydrogen enhanced localized flow softening effect was coupled within fracture strain dependency on stress triaxiality. Then, the numerical implementation and identification process of model parameters was described. Model parameters of the investigated steels were determined based on experiment results from literatures. Finally, with the calibrated model, fracture toughness reduction of the steels was predicted in a wide range of hydrogen pressure. The prediction results were compared with experimental results. Reasonable accuracy was reached. The proposed method is an attempt to reach balance between physical accurate prediction and engineering practicality. It is promising to provide a simplified numerical tool for the design and fit for service evaluation of hydrogen storage vessels. • Hydrogen embrittlement prediction model with few parameters was proposed. • Identification of model parameters with a few support of experiments. • Simplified Fracture toughness prediction model with acceptable accuracy. [ABSTRACT FROM AUTHOR]

In this study, AZ61 alloy processed by equal channel angular pressing (ECAP) method, is presented. This research seeks to find out the relationship that exists between the microstructure of the AZ61-magnesium alloy doped with SiC and Ni and processed by ECAP in terms of hydrogen storage properties. The results indicate that grain size reduces nearly 10 times after 4 passes of ECAP. Homogeneous distribution of the SiC in the metal matrix composite (MMC) and dynamic recrystallization are also observed. There is a gradual reduction in the grain size when the number of ECAP passes are increased. This microstructural refinement induced by ECAP improves the storage capacity and reaction kinetics of the alloy. Besides, the addition of Ni catalyst achieves faster absorption and desorption kinetics. However, it does not change its capacity. Ni reacts with Mg to form an intermetallic, which is hydrogen-absorbing, which in turn, catalyzes the reaction. Apart from introducing defects, the ECAP process also produces Mg/Al intermetallic, which acts catalytically. It is shown that SiC-doped AZ61-magnesium alloy can absorb and desorb 6.8 wt% H 2 at 648 K and 50 atm. • AZ61 with SiC and Ni additives prepared by gravity stir casting method. • Dispersion characteristics of the particles influences the rate limiting factors. • AZ61-1 wt%SiC achieves a hydrogen capacity of 6.8 wt%. • Performance declines to 6.5 wt% when Ni catalyst is added. • Combining SiC and Ni shows improved kinetics. [ABSTRACT FROM AUTHOR]

In this study, the hydrogen storage performance of commercial AZ31-Mg alloys combined with various allotropes of carbon was investigated and the microstructural modifications with respect to plastic deformation and high energy milling techniques investigated, with the aim of obtaining enhanced hydrogen storage efficiency. The hydrogen storage performance of alloys prepared with different weight ratios of carbonaceous materials as a catalyst was monitored in order to explore the effective improvement in hydrogen storage performance through microstructural modification. Additionally, the effects of different processing methods such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were also observed. AZ31 Mg based composites with various carbon additives were produced through gravity resistance casting and their micrographic structures examined through optical Microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The average particle size distributions of the sample powders were also measured. The rate of hydrogenation kinetics was calculated by a Sievert's type apparatus. Significant enhancement of the hydrogenation performance was obtained with the addition of carbonaceous materials. Overall, the hydrogen storage performance after ECAP deformation of the AZ31-3CB (carbon Black) composite showed a gain in the maximum capacity of 6.72 ± 0.05 wt%. Similar, after milling of the AZ31-3G (Graphene) composite materials, a maximum potential capacity of 6.83 ± 0.04 wt% was attained within 792 ± 144.34 s, with desorption of the entire H 2 content in 143.2 ± 26.09 s. The obtained results revealed significant improvement in the hydrogen storage capacity of AZ31-Mg alloys with the addition of carbon materials and with respect to plastic deformation and milling techniques. Graphical illustration of sample preparation process flow. Image 1 • AZ31/Carbonaceous additives fabricated by Gravity resistance casting method. • Carbonaceous addition modifies the microstructure of AZ31 alloy. • AZ31-3G (Graphene)-HEBM reaches the H 2 capacity of 6.83 ± 0.04 wt% in 792 s. • HEBM exhibits enhanced hydrogenation properties than ECAP for AZ31-3G (Graphene). [ABSTRACT FROM AUTHOR]

Abstract In this work, the hydrogen sorption properties of AZ31 magnesium alloys with various additions of nickel (Ni) (i.e., Ni (X = 0, 2, 4) wt.%) were investigated. Cast ingots with different AZ31/Ni P compositions were fabricated using a gravitating mechanical stir casting (GMSC) method. Two different processes, namely, equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were performed to improve its hydrogen storage properties. The particle size of the sample powders were measured by laser diffraction analysis. The microstructures, powder morphologies, and phase transformation were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hydrogen sorption kinetics were measured by a Sievert's type apparatus. The results showing the impact of the ECAP and HEBM processes on the hydrogen storage properties were compared. The AZ31-4 Ni ECAP processed sample showed a maximum hydrogen storage capacity of 7.0 wt.% at 2322 s with complete desorption of all the hydrogen in less than 5 min at a temperature of 375 °C. On the other hand, the pure AZ31 alloy which was treated with the HEBM process showed the maximum hydrogen capacity of 6.5 wt.% at 2393 s with desorption of all the hydrogen within 6 min. In addition, the activation energy, as illustrated by the Kissinger plot, revealed that the activation energy of the ECAP processed AZ31-4 Ni was 104.73 (KJ/mol), obviously lower than the material processed by HEBM and pure MgH 2. Graphical abstract Image 1 Highlights • Alloy composition fabricated by GMSC method. • AZ31-4Ni-ECAP reaches the H 2 storing capacity of 7.0 wt.%. • AZ31-4Ni-ECAP alloy exhibits activation Energy of (104.73 kJ/mol). • ECAP shows better results than HEBM. [ABSTRACT FROM AUTHOR]

In this study, commercial AZ31 Mg alloys were processed by equal channel angular pressing (ECAP) to study the effects of processing route and numbers of passes on hydrogen storage properties of AZ31 alloys. Furthermore, Mg-based metal matrix composites (MMCs) were fabricated by gravimetric casting of AZ31 alloy, activated carbon and Ni to investigate the effect of additives on hydrogen storage properties. The results indicated that kinetics of hydrogen uptake increased with the increasing number of pass. AZ31 processed by ECAP route B c with 8 passes had hydrogen capacity of 7.0 wt%, and demonstrated the highest grain refinement and the fastest hydrogen absorption kinetics. With the addition of 5 wt% of activated carbon and 0.5 wt% Ni, the hydrogen sorption kinetics of MMCs was enhanced and was comparable to that of the AZ31 processed by ECAP with 8 passes; however, in exchange for the improved kinetics, the hydrogen storage capacity was lowered to 6.3 wt%. To enhance hydrogen absorption kinetics, adding catalysts in the casting process could be more efficient than post-casting ECAP treatment if saving processing time is the priority. [ABSTRACT FROM AUTHOR]

Cast commercial AZ61 magnesium alloys were processed through equal channel angular pressing (ECAP) and were comminuted into chips by filing with a rasp in order to measure their hydrogen storage properties. The effects of the number of ECAP passes and the processing route of ECAP on the hydrogen storage properties of AZ61 magnesium alloys were investigated. ECAP processing led to severe dynamic recrystallization and grain refinement of the AZ61 alloys. Of the analyzed samples, the AZ61 alloy processed via the Bc ECAP route with eight passes exhibited the smallest grain size, the fastest hydrogen absorption and desorption rates, and the highest gravimetric hydrogen storage capacity of 6.2 wt%. [ABSTRACT FROM AUTHOR]

We studied the hydrogen storage properties of commercial AZ31 and AZ91 magnesium alloys with refined microstructure. Various processing techniques, such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM), were utilized to modify the microstructure and phase composition of the alloys. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical digital microscopy (ODM) were utilized to characterise the microstructure and phase transformations during the hydrogen absorption/desorption processes. The isothermal kinetics are measured by a Sieverts'-type apparatus at the temperature of 350 ℃. In the ECAP process, the AZ31 alloy had a slightly higher storage capacity and faster absorption kinetics, absorbing 6.0 wt% (6.6 wt% - maximum) of hydrogen in less than 12 min. In the HEBM process, AZ91 absorbed 6.5 wt% of hydrogen and desorbed it in 347 ± 13 s, a faster rate than AZ31. The pressure–composition isotherms of all studied alloys at a temperature of 300 °C were determined. The processed alloys exhibited no pressure hysteresis. The microstructure of bulk samples and the morphology of prepared powders were shown to affect their hydrogenation behaviour. The activation energies for hydrogen desorption were 119 ± 2 kJ/mol for AZ31 alloy processed by ECAP and 128 ± 3 kJ/mol for AZ91 alloy processed by HEBM, which are significantly lower than the activation energy values of pure Mg hydride. • Hydrogen storage properties of commercial AZ31 and AZ91 alloys are studied. • The ECAP and HEBM processes were employed to enhance hydrogen storage performance. • Both processes significantly improved the kinetic and thermodynamics properties. • The processed alloys exhibited no pressure hysteresis • The activation energies reduced to 119 ± 5 kJ/mol for AZ31-ECAP and 128 ± 5 kJ/mol for AZ91-HEBM. [ABSTRACT FROM AUTHOR]

• The highest temperature of 82.972 °C is located at the bottom of cylinder. • The flow velocity increases to 202.41 m/s at the first second and then decreases. • The temperature rises to maximum exponentially at the first 30 s of filling. • The temperature is almost above 85 °C except for the first 10 s when the ambient is 40 °C. Hydrogen has been considered a feasible energy carrier for fuel cell vehicles (FCVs), which offers a clean and efficient alternative for transportation. The hydrogen is filled from high-pressure stations into hydrogen storage systems (HSS) in FCVs. During the refueling of high-pressure hydrogen, it can cause a rapid increase in temperature in the HSS due to the thermal characteristics of the system leading to safety problems. For safety reasons, the tank's maximum temperature and fueling pressure are limited to less than 85 oC and 125% of the vessel design pressure, respectively. This paper presents the fast-filling process of hydrogen tanks through experiments and simulations based on Computational Fluid Dynamics (CFD). Several critical parameters, such as the initial pressure, the initial temperature of hydrogen, and the filling rate that can contribute to the temperature rise, are investigated during the fast-filling process. The temperature within the tank increase with the decrease of initial pressure and the increase of ambient temperature with less filling time. In the case of a linear pressure increase from 2 to 35 MPa within 180 s at the ambient temperature of 20 oC, the maximum temperature reached 82.97 °C. In addition, the average velocity of the inlet gas of the hydrogen cylinder increases to 202.41 m/s rapidly in the first second and then decreases to 14.3 m/s slowly for the remaining filling process. For an ambient temperature of 40 oC, the maximum temperature can reach 101.24 oC during the process except for the first 10 s when the gas temperature within the tank was consistently above 85 oC, causing significant damage to the cylinder. As a result, reasonable and effective fast-filling strategies are designed to ensure safety at high ambient temperatures. [ABSTRACT FROM AUTHOR]