Hydrogen In Aluminum Research Articles

Dissolution of hydrogen in metals and casting alloys

Thermodynamic calculations have shown that hydrogen from atmospheric water vapors can penetrate aluminum, iron and copper, especially into their melts. Hydrogen atoms in these metals are in free and adsorbed states. Strong and dense oxide films on the surfaces of aluminum, iron and copper significantly reduce the solubility of hydrogen in these metals. Copper and iron nanocrystals more actively adsorb atomic hydrogen than aluminum nanocrystals. This is one of the main reasons for the weak solubility of hydrogen in aluminum and the large desorption of hydrogen atoms in the crystallization of aluminum compared to iron and copper.

Melt sampling for hydrogen analysis optimized with the help of computer simulation

This research was carried out in laboratory conditions on a semi-continuous ingot casting machine owned by the Siberian Federal University. The paper compares the results of computer simulation carried out for AK12 alloy solidification process in the PoligonSoft programme. A new original mould is described designed for sampling liquid aluminium and its alloys for hydrogen analysis. The new mould has a larger surface area and walls that are made in the form of a heat exchanger intended for more efficient heat removal. It is shown that, in the commonly used Rensley mould, the melt solidifies in 14 seconds at the metal crystallization rate in the range from the pouring temperature to the solidus temperature of 15 oC/s, while in the case of the new mould these parameters are 12 seconds and 17.5 oC/s, correspondingly. The paper also compares the results of dissolved hydrogen analysis obtained when sampling was done with both the conventional Rensley mould and the new one. It was found that the concentration of hydrogen in the samples taken with the Rensley mould is lower on average by 0.01 cm3/100 g Al than in the samples taken with the new mould. Based on the results of the study, a conclusion was drawn that the proposed mould design delivers an additional advantage when sampling liquid metal. It also helps determine the concentration of dissolved hydrogen in molten aluminium with a higher degree of accuracy.This research was carried out by the Siberian Federal University as part of the governmental assignment for research; Project No. FSRZ-2020-0013.

Mysterious Field Evaporation Behavior of Hydrogen in Aluminium Based Material Analyzed with Atom Probe Tomography

Mysterious Field Evaporation Behavior of Hydrogen in Aluminium Based Material Analyzed with Atom Probe Tomography

Preparation of Ceramic Foam Filters With a Lithium-Containing Surface

Hydrogen in aluminum causes the formation of detrimental hydrogen porosity in castings. In order to reduce the formation of hydrogen pores, an approach was targeted using lithium as target for hydrogen. This approach utilizes the affinity of lithium for hydrogen, whereby spodumene (a lithium aluminum silicate) and lithium aluminate were used as lithium providers. Within the scope of this study, the preparation of ceramic foam filters with a coating of lithium-containing raw materials (spodumene) was investigated. Those investigations revealed that the spodumene coating has a detrimental influence on the bending strength of the foams when a certain level of spodumene is exceeded. This observation might be explainable by the intrusion of the spodumene into the alumina matrix of the skeleton foam. Two wetting tests at different temperatures were conducted, verifying the significant influence of the temperature on the reaction between the spodumene and AlSi7Mg. Furthermore, test filters coated with raw materials exhibiting different amounts of lithium were conducted. The hydrogen pores were evaluated by light microscopy and computed tomography. The analyzed pore size distribution in the aluminum did not elucidate the proximate influence of the lithium-coating on the ceramic foam filter on the hydrogen porosity in the aluminum.

Hydrogen Solubility in Liquid and Solid Pure Aluminum—Critical Review of Measurement Methodologies and Reported Values

Reliable information on the solubility of hydrogen in aluminum and its alloys is critical to the effort of the aluminum industry to control and ameliorate the usually deleterious effects of hydrogen on the properties and performance of pure aluminum and aluminum alloy products. Unfortunately, there is a significant disparity between published values of hydrogen solubility in pure aluminum and aluminum alloys. This is because the measurement of the extremely low soluble hydrogen concentration in aluminum and its alloys is experimentally difficult. Also, the reproducibility, accuracy, and reliability of the hydrogen solubility values are very sensitive to the measurement techniques, test conditions, chemical composition, and state of the aluminum sample. Thus, no serious discussion of the reliability of reported values of hydrogen solubility in aluminum and its alloys can be undertaken without a critical assessment of the fundamental principles of the experimental techniques used in the determination of the reported values. In this article, a critical review of the fundamental principles of the experimental techniques used in the measurement of hydrogen solubility in liquid and solid pure aluminum and aluminum alloys is presented. In addition, the reliability and possible accuracy of reported values of hydrogen solubility in solid and liquid pure aluminum are critically assessed. Empirical equations for calculating hydrogen solubility in liquid and solid pure aluminum as a function of temperature and pressure, derived from the most reliable sets of data are recommended. At 101.3 kPa (1 atm.) hydrogen partial pressure, the most reliable values of hydrogen solubility at the melting point (833 K) of pure aluminum are 0.71 cm3/100g (i.e., 6.32 × 10-5 wt.% H) and 0.043 cm3/100g (i.e., 3.81 × 10-6 wt.% H), in the liquid and solid state, respectively. So, the partition coefficient of hydrogen in pure aluminum is 0.061.

Hydrogen Absorption and Desorption Behavior on Aluminum-Coated Hot-Stamped Boron Steel during Hot Press Forming and Automotive Manufacturing Processes.

Our study mainly focused on diffusible hydrogen in aluminum–silicon-coated hot-stamped boron steel during a hot press forming process and in pre-treatment sequential lines of the automotive manufacturing process using a thermal desorption spectroscopy (TDS) technique. First, in the hot stamping procedure, as the soaking time increased in the heating furnace at a specific dew point when austenitizing, a high concentration of diffusible hydrogen was absorbed into the hot-stamped boron steel. Based on the TDS analysis of hydrogen absorbed from hot stamping, the activation energy value of hydrogen trapping in 1.8 GPa grade steel is lower than that of 1.5 GPa grade steel. This means that diffusible hydrogen can be more easily diffused into defective sites of the microstructure at a higher level of the tensile strength grade. Second, in sequential pre-treatment lines of the automotive manufacturing process, additional hydrogen did not flow into the surface, and an electro-deposition process, including a baking procedure, was effective in removing diffusible hydrogen, which was similar to the residual hydrogen of the as-received state (i.e., initial cold rolled blank). Based on these results, the hydrogen absorption was facilitated during hot press forming, but the hydrogen was sequentially desorbed during automotive sequential lines on aluminum-coated hot-stamped steel parts.

Technology and equipment for isolated aluminum melt overflow from a vacuum transport ladle with using the siphon

The work was performed at the Sayanogorsk aluminum plant UC RUSAL in the technological scheme from an aluminum cell to an alloying furnace. The article presents comparative results of studies of the dynamics of saturation of aluminum with hydrogen when using a vacuum transport ladle with a closed (siphon) cast metal overflow and the existing technology of overflow. The basic design of a vacuum transport ladle with a removable siphon is presented. It is shown that one of the main sources of saturation of aluminum melt with hydrogen is its interaction with air moisture during open overflows of metal during its movement from the cell to the alloying furnace. During the study, it was found that pouring aluminum from the cell using traditional technology increases the hydrogen content by an average of 0.045 cm3/100 g Al, and pouring aluminum from the cell with an experimental ladle with a siphon increases the concentration of hydrogen in the metal by an average of 0.029 cm3/100 g Al. It was found that when pouring aluminum from the ladle into the alloying furnace using traditional technology, the hydrogen content increases from 0.220 cm3/100 g Al to 0.297 cm3/100 g Al, and when using a vacuum transport ladle with a closed (siphon) overflow, the hydrogen content decreases from 0.189 cm3/100 g Al to 0.161 cm3/100 g Al. It is shown that an additional advantage of pouring aluminum melt with an experimental vacuum transport ladle with a closed (siphon) overflow is to reduce the amount of dross removed from the metal surface, as well as to reduce metal losses due to oxidation of the melt. The specific dross formation according to the existing overflow technology was 1,962 kg/t Al, and when using an experimental vacuum pump with a closed (siphon) overflow, the specific formation of dross was 1,204 kg/t Al.The work was performed using the results of research conducted during the implementation of project 14.578.21.0193 from October 3 for the period 2016–2018. “Development of theoretical and technological solutions for reducing hydrogen in aluminum and low-alloy aluminum alloys” in the framework of the Federal target program “Research and development in priority areas of development of the scientific and technological complex of Russia for 2014–2020” with financial support from the Ministry of education and science of Russia.

Retention characteristics of hydrogen in pure aluminum and duralumin with cold-working

Behavior of hydrogen trapping in defects induced by cold-working (CW) of pure aluminum (Al) and Duralumin (A2017) were examined by thermal desorption analysis (TDA). The total desorption amount of deuterium in pure Al and A2017 increased with the working rate of CW; the desorption amount for hydrogen trapped at dislocations increased though that at vacancies and their clusters was likely saturated. Strong hydrogen trapping was observed in A2017, which disappeared by CW.

Hydrogen diffusivity and solubility in stressed fcc crystals

Although many materials are used under extreme conditions, the effects of stress and strain are often neglected in material studies, especially when studying the solubility or calculating the diffusivity of substitutional or interstitial species. In this work, a general method based on first-principles calculations and elasticity theory in fcc systems is presented to fill this gap. The case of hydrogen in aluminum is investigated in detail as an application sample by comparing results from the density functional theory (DFT) and the elasticity theory. Additional systems, Ni, Cu and Pd, are also examined for hydrogen but in the framework of the elasticity theory only. Different types of stresses, i.e. hydrostatic, multi-axial and shear stress, are investigated for comparison purposes. The symmetry break induced by the loading is analyzed at the atomic scale by calculating the jump rates, at macroscopic scale from computed diffusion coefficients. Equations of diffusion are developed for each loading. Results show that the effect of loading on atomic parameters – insertion energies, energy barriers, etc.– can be accurately captured by the elasticity theory in terms of elementary parameters calculated using the DFT. Results show that the effect of stress is weak in the case of hydrogen.

Nanoporous Aluminum for Solid-State Hydrogen Storage

Effective hydrogen storage is still a challenge because the common approach to store hydrogen gas mechanically compressed in cylinders can be unsafe due to the high pressure and flammability risks involved. A promising alternative is solid-state hydrogen storage in lightweight materials. In this work, we explore ways to store hydrogen in ultrafine nanoporous aluminum during real-time fabrication of this nanoporous aluminum. Here I will present our novel scalable air-free synthesis method for ultrafine and oxide-free nanoporous aluminum with structure size in the range of 10-20 nm via selective electrolytic dealloying [1,2] and show how we extend this method to incorporate hydrogen in this nanoporous aluminum. Hydrogen can then be released by heating the material at moderate temperatures (~130°C). This method of hydrogen storage can find great use in on-board hydrogen storage for vehicular applications. [1] J.S. Corsi, J. Fu, Z. Wang, T. Lee, A. K. Ng, and E. Detsi: ACS Sustainable Chem. Eng. 7 (2019). [2] T. Lee, J. Fu, V. Basile, J. Corsi, Z. Wang, and E. Detsi: Under Review.

The Effect of Hydrogen on Pore Formation in Aluminum Alloy Castings: Myth Versus Reality

The solubility of hydrogen in liquid and solid aluminum is reviewed. Based on classical nucleation theory, it is shown that pores cannot nucleate either homogeneously or heterogeneously in liquid aluminum. Results of in situ studies on pore formation show that pores appear at low hydrogen supersaturation levels, bypassing nucleation completely. The results are explained based on the bifilm theory introduced by Prof. John Campbell, as this theory is currently the most appropriate, and most likely, the only mechanism for pores to form. Examples for the effect of hydrogen on pore formation are given by using extreme data from the literature. It is concluded that a fundamental change in how hydrogen is viewed is needed in aluminum casting industry.

Solubility of hydrogen in liquid aluminium: reanalysis of available data

ABSTRACTData for solubility of hydrogen in liquid aluminium from 17 studies have been reanalysed, based on the concept that solubility refers to maximum concentration that can be held in solution. Analysis has shown that maximum points clearly follow a trend. These maximum points are recommended as the best available data for hydrogen solubility in liquid Al. A new solubility equation based on the maximum data is provided, which estimates a solubility that is 33% higher than the solubility equation widely accepted in the literature.

Formation of surface layer of hydrogen in pure aluminum

Hydrogen atom behavior in pure aluminum is described by ab initio modelling. All main energy characteristics of the system consisting of hydrogen atoms in a periodic aluminum crystal are found.

Theoretical Calculations of the Foaming Properties of Powder Agents for the Production of Aluminium Foams

This paper presents the theoretical calculations of the foaming process of selected powder foaming agents (TiH2, CaH2, MgH2, ZrH2, CaCO3 and MgCO3) regarding the volume of gas, relative density and density of the metal foam obtained with respect to the use of a certain amount of powdered blowing agent. This work is carried out in the frame of the university project in which a small subproject is dealing with the problem of the cellular lightweight metal structures. Furthermore by calculating the diffusion of hydrogen in both solid and liquid aluminium there were found results for the duration of the anticipated action of the powdered blowing agent (0.75, 1.0, 1.25, 1.50, 1.75 and 2.0 wt. %).

Formation of Surface Hydrogen Layer in Pure Aluminum

By quantum chemistry, the behavior of hydrogen in pure aluminum was described, and the key energy characteristics of a system consisting of hydrogen atoms in a periodic aluminum crystal were calculated.

Effective Degassing for Reduced Variability in High-Pressure Die Casting Performance

The reduced solubility of hydrogen in molten aluminium is believed to be a key factor influencing the formation of gas porosity, which adversely affects the mechanical properties. In this study, two crucibles of AlSi10MnMg alloy were degassed using conventional rotary degassing and high shear melt conditioning (HSMC) respectively and then cast into tensile specimens using the high-pressure die casting (HPDC) process. An optimal holding time of 10 min was established for both processing techniques corresponding to reduced density index (DI) and reduced variation in tensile performance. After rotary degassing, DI values were found to increase with increasing holding times, rising to 4.1% after 70 min. For HSMC, a quasi-steady state was observed with a maximum DI value of 1.4% after 190 min. The pore size in HPDC cast specimens was observed to be considerably lower after degassing with the HSMC device compared with rotary degassing.

Investigations on dual laser beam welding of aluminum high pressure die castings at reduced ambient pressure

During the manufacture of aluminum high pressure die castings, the aluminum alloy is in a liquid phase during the majority of process steps. Due to the high solubility of hydrogen in liquid aluminum, the die casted part likely has an increased hydrogen content, which affects the weldability negatively. When welding these materials, hydrides dissociate and hydrogen is liberated and forms porosity during solidification. To avoid the described formation of porosity, friction stir welding below the melting point and electron beam welding with high frequency beam oscillation were investigated in prior research. Other studies reported that the formation of porosity during laser beam welding of pure aluminum was prevented by the application of dual beam configurations. However, it is well known that laser beam welding under vacuum condition has several advantages, such as the increase in penetration depth, the enhanced degasification, or the overall calming effect on the melt pool when welding ferrous metals. Aiming to combine these advantages, the current work consequently focuses on the occurrence of porosity during dual laser beam welding of aluminum die castings under vacuum (100–0.1 hPa) and atmospheric conditions. All results are based on the outcome of x-ray computed tomography or tensile testing.

Thermal Desorption Spectroscopy Study on the Hydrogen Behavior in a Plasma-Charged Aluminum

Hydrogen in aluminum has been known to be the cause of blister and pore. Some aluminum alloy is susceptible to stress corrosion cracking, which is based on intergranular cracking arisen from hydrogen embrittlement. The behavior of hydrogen in aluminum has not been fully understood yet. Hydrogen gas plasma enables to introduce high hydrogen concentrations into specimen without Al (OH)3 layer on the surface of specimen. In this paper, we have investigated the behavior of hydrogen in a plasma charged aluminum by means of thermal desorption spectroscopy, a method to evaluate the amount and trap states of hydrogen. Cold-rolled pure aluminum were annealed, electro-polished and charged with hydrogen gas plasma. Immediately after hydrogen gas plasma charging, TDS tests were performed under ultra-high vacuum. The hydrogen desorption spectrums obtained by TDS tests had three peaks corresponding to the co-diffusion of hydrogen-vacancy pair, dislocation and pore. Compared to a sample without charging, in a plasma charged sample, the amount of hydrogen trapped in vacancies especially increased.

Role of impurities, defects and their complexes on the trapping of hydrogen in bulk aluminum and on the Al(1 1 1) surface

First principles calculations are performed to explore and quantify the stability of hydrogen in several Al environments including bulk Al and Al(111) surface, with the possible presence of vacancies and Mg, Cu and Zn impurities as substitutional defects in bulk or in the surface or as adatoms on the surface. In contrast to common statement, we show that hydrogen has a natural propensity to self-organize in bulk Al and demonstrate that vacancies can serve as nucleation centers for this process leading to massive hydrogen accumulation into aluminum. We then discuss the surface adatom defect and observe that it activates molecular hydrogen dissociation enabling further hydride insertion into bulk Al. Finally, we find that Mg, Cu, or Zn isolated impurities do not significantly impact hydrogen trapping indicating that structural defects rather than the local chemistry of isolated impurities are governing hydrogen accumulation in aluminum.

Ab initio study of boron and aluminum hydrides nanoparticles

Using Density Functional Theory (DFT), the desorption energies of Hydrogen in Aluminum, and Boron nanoparticles (NPs) is calculated. The type of NPs studied here, were MnHm with M = Al or B, n varying from 2 up to 20 and m/n between 0 and 3. NPs combining the two atoms (Aln−xBxH3n) were also examined. These types of clusters combine the low weight of B with the low desorption energies of Al. For each NP, several different geometries were studied in order to find the one with the lowest energy.