Al Precipitation Research Articles

Effect of heat treatment on microstructure and mechanical properties of a Fe-12.2Cr-10Ni-1Mo-1Ti-0.6Al precipitation hardening-stainless steel manufactured via laser powder bed fusion

Effect of heat treatment on microstructure and mechanical properties of a Fe-12.2Cr-10Ni-1Mo-1Ti-0.6Al precipitation hardening-stainless steel manufactured via laser powder bed fusion

An H3O-alunite method for production of smelter grade alumina from an ammonium alum solution after high-pressure acid leaching of coal fly ash

Precipitation of H3O-alunite from an ammonium alum solution using boehmite as a seed was studied. The ammonium alum solution was obtained after high-pressure leaching of mullite-type coal fly ash (CFA) with a mixture of 7.5 M H2SO4 + 40% NH4HSO4 at 200 °C. Fe(III) was extracted from the ammonium alum solution by ion exchange sorption using the Purolite S957 resin. Effects of temperature (70–90 °C), seed boehmite (100–400 g/l), ammonium alum (60–240 g/l), and precipitation duration (2–8 h) on the Al precipitation degree were evaluated. Calcination of the precipitate at 300–950 °C to obtain alumina powder was studied next. Concentration of impurities, specific surface area, phase composition, morphology, and the average particle size distribution of alumina powders were investigated. The results show that smelter grade alumina (SGA) can be obtained at optimized parameters of precipitation and calcination.

Nanoscale Al precipitation in the Si phase in AlSi10Mg alloy during electron beam powder bed fusion

Additive manufacturing of Al alloys has garnered attention in the aerospace and automobile industries. This is the first study on the formation of nanoscale Al precipitates in the Si phase of an AlSi10Mg alloy during electron beam powder bed fusion (EB-PBF). Spherical Si particles were homogeneously dispersed in the Al matrix, highlighting the difference from the laser beam PBF (LB-PBF) microstructures. Nanoscale Al phase was formed with a crystallographic orientation relationship with the surrounding Si phase: (111)Si//(111)Al and [11¯0]Si//[11¯0]Al. The formation of Al nanoprecipitates was attributed to an interplay between non-equilibrium solidification, wherein excess Al was dissolved in the Si particles, and the subsequent decomposition of the supersaturated Si phase during high-temperature exposure owing to the preheating procedure. To the best of our knowledge, such formation of Al nanoparticles has not been reported in AlSi10Mg produced through conventional processing or LB-PBF. Thus, the unique thermal history of EB-PBF provides novel opportunities for microstructural evolution, which may be beneficial for the development of novel Al-based alloys.

Effect of Aging Treatment on the Strength and Microstructure of 7075-Based Alloys Containing 2% Li and/or 0.12% Sc

The present study was performed on three versions of 7075 alloy to which Sc or Sc + Li was added. The alloys were subjected to various aging treatments. The microhardness results show that the highest value of hardness was achieved when the alloy containing Li + Sc was aged at 120 °C for 24 h whereas the minimum level was exhibited by the base alloy aged at 280 °C. The results were interpreted in terms of the size and distribution of the main hardening phase (η′(MgZn2)), and the role of the presence of Al and Cu in the used alloy. Precipitation of Al3(Sc, Zr, Ti) phase particles during solidification of the Sc-containing ingots was also discussed. The coarsening and spheroidi-zation of η-phase particles take place through the Ostwald ripening mechanism while smaller par-ticles in solution dissolve and deposit on larger particles. In Sc-containing alloys, star phase particle consists of different layers. The change in the brightness from layer to layer indicates that the Zr and Sc concentrations are varied within the star phase, since the atomic number of Zr (40) is higher than the atomic number of Sc (21). The addition of Sc, as well, leads to marked decrease in the grain size of the as-cast alloys i.e., 300 µm and 45 µm, respectively. The interaction between Li and Sc would reduce the effectiveness of the grain refining effect of Sc. The results of the refining effect of Sc were confirmed using the EBSD technique.

Efficient extraction and recovery of lithium from waste aluminum cryolite electrolyte

The accumulation of alkali metals in cryolite electrolyte has negative impacts on the operation of aluminum electrolysis, and part of electrolytes need to be periodically replaced and discharged. A cleaner and efficient process was proposed to recover LiF and Al2(SO4)3 from the waste cryolite electrolyte. Under the optimum sulfated roasting conditions, 87.55% of Li and 30.30% of Al were leached. The obtained cryolite residue with a low molecular ratio could be returned to the aluminum electrolysis system. The addition of sodium benzoate achieved the efficient separation of Al3+ from Li-containing leachate, and the Al precipitation ratio was 99.78%. Acid leaching of the aluminum precipitate regenerated benzoic acid and recovered 99.62% of Al2(SO4)3. Finally high-purity cubic LiF was prepared from Li2SO4 solution, and the recovery of LiF was 98.78%.

Microstructure and Mechanical Properties of a Precipitation‐Strengthened Fe–Al–Nb Alloy

Fe–Al alloys provide an attractive property profile for applications at temperatures of up to 700 °C. Herein, a Fe–25Al–2Nb (at%) alloy is, manufactured on an application‐relevant scale. Preforms are cast and subsequently forged into a turbine blade shape. The microstructural evolution and mechanical properties, namely quasistatic strength and creep response, are tested in different manufacturing conditions and are compared to the properties of equilibrated laboratory alloys, as well as to literature results. The cast process leads to coarse‐grained initial nonequilibrium microstructures with lower amounts of Laves phase as compared to thermodynamic equilibrium. Forging at 900 °C leads to the significant formation of subgrains in the Fe–Al matrix and precipitation of the Laves phase. The as‐cast condition of Fe–25Al–2Nb exhibits a complex creep behavior governed by the transient formation of a coherent Heusler phase as well as Laves phase formation and recrystallization in later stages of creep. In the forged condition, the material behaves similarly to long‐term annealed material. Although Fe–25Al–2Nb has slightly lower strength and lower creep resistance over the entire temperature range tested, it performs well compared to Ta‐containing Fe–Al alloys due to its lower cost and density.

Insights on mechanisms of aluminum phytotoxicity mitigation by canola straw biochars from different regions

To better understand the amendment effects and mechanisms of aluminum (Al(III)) phytotoxicity mitigation by different regional crop straw biochars, wheat seedling root elongation trials were conducted. The contributions of liming effect, oxygen-containing surface functional group adsorption, and oxyanions precipitation to Al(III) phytotoxicity mitigation by Ca(OH)2, pristine and ash-free canola straw biochar were evaluated. The results indicated that biochars derived from canola straw collected from four different regions (Yingtan, Xuancheng, Nanjing, and Huaiyin) caused 22–70% wheat seedling root elongation, which might be linked to liming effect. Incorporation of the corresponding ash-free biochars caused 15–30% elongation, which could be attributed to the surface functional group adsorption. About 0–60% of changes could be explained by Al(III) precipitation with inorganic oxyanions. These findings provide new insights into the physicochemical properties, potential applications, efficiencies, and underlying mechanisms of crop straw biochar in alleviating Al(III) phytotoxicity, which is dependent on the cultivation soil, and indicate similar application of crop straw biochar for acidic soil amelioration, contaminated soil remediation, and arable soil improvement.Graphical

Corrosion behavior of aluminum alloy in simulated nuclear accident environments regarding the chemical effects in GSI-191

Long-term aluminum (Al) corrosion tests were designed to investigate the condition that would generate severe Al corrosion and precipitation. Buffer agents of sodium tetraborate (NaTB), trisodium phosphate (TSP) and sodium hydroxide (NaOH) were adopted. The insulation materials, fiberglass and calcium silicate (Ca-sil), were examined to explore their effects on Al corrosion. The results show that significant precipitates were formed in both NaTB/TSP-buffered solutions at high pH. The precipitates formed in NaTB solution raise more concerns on chemical effects in GSI-191. A passivation layer formed on the surfaces of coupon in solution with the presence of insulations could effectively mitigate Al corrosion. The Fe-enriched intermetallic particles (IPs) embedded in coupon appeared to serve as seeds to readily induce precipitation via providing extra area for heterogeneous Al hydroxide precipitation. X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses indicate that the precipitates are mainly boehmite (γ-AlOOH) and no direct evidence confirms the presence of sodium aluminum silicate or calcium phosphate.

Effects of nanosized precipitates on the Portevin-Le Chatelier behavior: Model prediction and experimental verification

The influence of homogenously-distributed nanosized Al3(Sc, Zr) precipitates on the Portevin-Le Chatelier (PLC) behavior in a model AlMgScZr alloy was investigated by experimental characterization and theoretical modeling. A remarkable advantage of the selected alloy is that the solute Mg concentration remains unchanged during the precipitation of Al3(Sc, Zr) nanoparticles, which effectively rules out the influence of solute concentration change on PLC. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) were used for quantitative characterization of precipitates and evaluation of key modeling parameters. By comparing the results for AlMg (without precipitates) and AlMgScZr (with precipitates) the effects of precipitates on the PLC phenomenon were clarified. It was found that the precipitates decrease the critical strain for the occurrence of PLC. Further, by evaluating dislocation densities of both alloys via synchrotron X-ray diffraction (XRD), the influence of precipitates on PLC was clarified by revealing the different roles of solute atoms and precipitates played in the dislocation-dislocation interaction. A model was proposed to account for these phenomena.

Experimental simulations of Zn[sbnd]Pb slag weathering and its impact on the environment: Effects of acid rain, soil solution, and microbial activity

Slag heaps are far from stable and evolve continuously from the time they are deposited. In the studied site (Świętochłowice, Upper Silesian Industrial Region, Poland), the major change in the slag heap has involved the formation of fine-grained strongly weathered material. Possible conditions of slag weathering, as well as any impacts of weathered material on the environment, have been evaluated by weathering experiments. The experiment simulating acid rain at adjusted pH = 4 precisely reproduced many features of the weathering transformations observed in nature, such as strong disintegration of slag material, formation of abundant Fe(hydro)oxides, silica and alumina removal, and Pb precipitation. Conversely, bioweathering with Acidithiobacillus thiooxidans often showed the opposite direction of transformations (Si and Al precipitation, Pb removal, transformations at the rims of larger slag particles), probably due to the too-aggressive low pH of the simulations. There are environmental consequences as more and more slag in the heap weathers, with fresh slag releasing mostly Zn and Ba. On the other hand, weathered slag material may release high contents of Pb, Cd, As, but only if the pH remains at 4–6. In present-day slag heap conditions, precipitation of Fe(hydro)oxides and other secondary phases diminishes toxic element mobility. However, soils and sediments surrounding the heap show high levels of contamination (up to 2500 mg/kg for Pb, up to 11,300 mg/kg for Zn, up to 120 mg/kg for Cd), which is perhaps due to leaching of weathered slag or its mechanical removal. Other contaminants include smelter emissions and high Ba and Hg components that are tentatively linked to the episode of early weathering of fresh slag.

A study into the behaviour of nickel, cobalt and metal impurities during partial neutralisation of synthetic nickel laterite pressure leach solutions and pulps

The behaviour of nickel (Ni), cobalt (Co) and major impurities such as aluminium (Al), trivalent chromium [Cr(III)] and ferric iron [Fe(III)] during the partial neutralisation of synthetic pressure acid leach (PAL) liquors and pulps was investigated. Ferric iron precipitation took place between pH85°C 2 to 3, and up to 54% of Cr(III) and 42% of Al were co-precipitated with Fe(III). Haematite appeared to act as a seed and promote the removal of Fe(III) from solution at a pH85°C as low as 2. Precipitation of the remaining Al and Cr(III) from solution did not commence until at or above pH85°C 3.5, and virtually went to completion at pH85°C 4 (96% precipitation extent). There was a linear correlation between the %Cr(III) precipitation and %Al precipitation from solution, which suggests that the behaviour of the two species is related and that Cr(III) is unlikely to behave independently in solution. Nickel and cobalt losses were strongly dependent on pulp pH, and valuable metal losses rapidly climbed above pH85°C 3 and further increased after 1 h of ageing; this behaviour appears to be consistent with adsorption processes. Cobalt losses were found to increase significantly in the presence of haematite whilst Ni losses were unchanged, suggesting that there is partitioning of Ni and Co during partial neutralisation of PAL pulps with Co preferentially adsorbing onto haematite. Final Ni losses were on average 1.95% and were unaffected by the presence of haematite; final Co losses were 0.38% in the absence of haematite and increased to 3.30% in the presence of haematite.

RECOVERY OF METALS FROM ELECTROACTIVE COMPONENTS OF SPENT Ni-MH BATTERIES AFTER LEACHING WITH FORMIC ACID

this work describes a route for recovering nickel, cobalt, iron, zinc and lanthanides from spent nickel-metal hydride batteries. Formic acid was used as leachant. Experiments were run at 25-50°C for 1-4 h. Under the best conditions leaching yields surpassed 99 wt.%, except for iron. The insoluble matter contains almost solely iron as iron(III) basic formate. The leachate went through six separation procedures, combining solvent extraction with D2EHPA as extractant, and precipitation reactions. Fe2+ and Zn2+ were extracted together (> 99 wt.%) from the original leachate (pH ~1.5). Yttrium and lanthanides were precipitated as oxalates directly from the raffinate (> 99.9 wt.%) upon addition of sodium oxalate. In the next steps, Mn2+ and Co2+ were extracted with D2EHPA at buffered pH (3 and ~4.8, respectively), after adding NaOHaq. About 10 wt.% of leached Ni2+ was coextracted with Co2+. The remaining Ni2+ was precipitated from the raffinate after addition of aqueous sodium oxalate at pH 6. After precipitation of Al3+ upon addition of NaOHaq. until pH ~8, sodium formate was recovered after slow evaporation of the final aqueous solution at 60oC. It contains ~90 wt.% of the formate present in the leachant.

Interaction of Si and Al and Its Effect on AlN Precipitation in Ferritic Fe at 1373 K to 1473 K

To investigate the effect of Si on Al and AlN precipitation in ferritic Fe, high-temperature thermochemical equilibrium experiments were conducted on Fe-Si-Al foils and Ag-Si-Al alloys at 1373 K, 1423 K, and 1473 K. Using the activity coefficient in the infinite dilute solution and the self-interaction parameter of Si in ferritic Fe, the interaction parameter between Si and Al in solidified ferritic Fe was found to be a positive value, which corresponds to a repulsive relationship. And its temperature dependence could be also determined as follows. $$ e_{\text{Al}}^{\text{Si}} = \frac{3025}{T} - 1.73 $$ Considering the effect of Si on the activity coefficient of Al, the solubility of AlN in ferrite Fe was investigated and compared with the conventional estimation. It could be confirmed that the stable region of AlN formation becomes larger due to the repulsive relationship between Si and Al in the present research.

Analysis of interface properties and associated void of nanoscale Al precipitates in Al-Si alloys: First-principles calculations and experiment

In this paper, the properties of the interface between nanoscale Al precipitate and Si matrix were studied by the first-principles calculations combined with high-resolution transmission electron microscopy (HRTEM) observation. The purpose of this work is to reveal its role on the mechanical properties of the eutectic Si particle in Al-Si alloys. Meanwhile, the formation mechanisms of the void associated with every Al precipitate were also discussed in depth. The most thermodynamically stable interface structure was obtained by the calculation of the work of adhesion (Wad) and interfacial energy (γint) of the 12 models of Al(11¯2)/Si(220) interface. By analyzing the electronic structure of the interface, such as charge density difference, and density of states (DOS), it is found that strong AlSi covalent bonds are formed at the interface, making the bonding strength higher than the inside of the Al precipitate. Therefore, the microcracks tend to form and propagate firstly inside the nanoscale Al precipitates instead of Al/Si interface. In order to explain the interesting phenomenon that there is always a void associated with every Al particle, the diffusion barrier of Al atom in the Si matrix and the binding energy of solute atom and a vacancy were calculated. The results show that the vacancies can be introduced by the change of the volume and the migration of the solute-vacancy pair during the diffusion and precipitation progress. Then these vacancies will be discharged along the close-packed direction (Al<111>) and gather at the Al{111}/Si{001} interface, forming the visible void. This agrees very well with the experimental observation.

The controlling role of atmosphere in dawsonite versus gibbsite precipitation from tetrahedral aluminate species.

In highly alkaline solution, aluminum speciates as the tetrahedrally coordinated aluminate monomer, Al(OH)4- and/or dimer Al2O(OH)62-, yet precipitates as octahedrally coordinated gibbsite (Al(OH)3). This tetrahedral to octahedral transformation governs Al precipitation, which is crucial to worldwide aluminum (Al) production, and to the retrieval and processing of Al-containing caustic high-level radioactive wastes. Despite its significance, the transformation pathway remains unknown. Here we explore the roles of atmospheric water and carbon dioxide in mediating the transformation of the tetrahedrally coordinated potassium aluminate dimer salt (K2Al2O(OH)6) to gibbsite versus potassium dawsonite (KAl(CO3)(OH)2). A combination of in situ attenuated total reflection infrared spectroscopy, ex situ micro X-ray diffraction, and multivariate curve resolution-alternating least squares chemometrics analysis reveals that humidity plays a key role in the transformation by limiting the amount of alkalinity neutralization by dissolved CO2. Lower humidity favors higher alkalinity and incorporation of carbonate species in the final Al product to form KAl(CO3)(OH)2. Higher humidity enables more acid generation that destabilizes dawsonite and favors gibbsite as the solubility limiting phase. This indicates that the transition from tetra- to octahedrally coordinated Al does not have to occur in bulk solution, as has often been hypothesized, but may instead occur in thin water films present on mineral surfaces in humid environments. Our findings suggest that phase selection can be controlled by humidity, which could enable new pathways to Al transformations useful to the Al processing industry, as well as improved understanding of phases that appear in caustic Al-bearing solutions exposed to atmospheric conditions.

Effect of Sc content on microstructure and properties of Al-Zn-Mg-Cu-Zr alloy

The effect of Sc content on microstructure and properties of Al-Zn-Mg-Cu-Zr alloy was studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), tensile tests, hardness measurements and corrosion evaluation. It is revealed that the increase in the volume fraction of the η' phase and the precipitation of Al3(Sc, Zr) particles within the alloy contribute to the significant grain refinement within the Al-7.0Zn-3.0 Mg-0.3Cu-0.15Sc-0.12 Zr (wt.%) alloy. The strength and hardness of the alloy have also been improved. Due to the addition of Sc element, the precipitates at the grain boundaries of the alloy become discontinuous, and the size of such precipitates is reduced. The population density is also decreased. Consequently, the alloy has excellent resistance to intergranular corrosion and exfoliation corrosion. Electrochemical data also shows that the alloys have a smaller tendency to corrode and slower corrosion rates.

Precipitation of Al3(Scx ,Ti1-x) Particles in Al-Mg-Sc-Ti Alloy

Precipitation of Al3(Scx ,Ti1-x) Particles in Al-Mg-Sc-Ti Alloy

MICROSTRUCTURAL EVOLUTION AND COARSENING KINETICS OF B2-(Fe,Ni)Al IN FERITIC STEEL OF Fe-14Ni-9Al-7,5Cr-1Mo AT HIGH TEMPERATURES.

MICROSTRUCTURAL EVOLUTION AND COARSENING KINETICS OF B2-(Fe,Ni)Al IN FERRITIC STEEL OF Fe-14Ni-9Al-7,5Cr-1Mo AT HIGH TEMPERATURES. Increasing the efficiency of power plant facilities, such as steam power plant, is demanding, and this drives to the development of materials capable for higher temperature operations. Ferritic steels have been widely used for boiler components due to their relatively economical and higher in thermal conductivity. Nevertheless, the application of ferritic steels for boilers is limited only at 630 ℃ due to their weakness in creep strength and corrosion at higher temperatures. Efforts to increase the performance of ferritic steels at higher temperature applications have been intensively carried out, one of which is by developing B2-(Fe,Ni)Al precipitates in the ferrite matrix. This paper discusses the microstructural evolution in alloy of Fe-14Ni-9Al-7.5Cr-1Mo (in wt.%) strengthened by B2-(Fe,Ni)Al precipitates during heating at 800, 900, and 1000 oC for 6, 20 and 48 hours. Ageing at 800 oC for 6 hours gave rounded cuboidal B2-(Fe,Ni)Al precipitates dispersed homogeneously in the ferrite matrix and changed to rounded shape at longer ageing times. At 1000 oC, however, the precipitates had rounded shape at all times of ageing. Coarsening of precipitates occurred during ageing at 800 and 1000 oC with the rate constants of 5,7 x 104 nm3/h and 2,1 x106 nm3/h respectively, which is considered relatively low. The highest hardness value of 520 HVN was observed for the sample aged at 1000 °C for 6 hours.Keywords: Ferritic steels, B2-(Fe,Ni)Al precipitate, coarsening, microstructure evolution

Microstructural evolution and mechanical properties of a newly designed steel fabricated by laser powder bed fusion

The M789 steel was designed by voestalpine group based on Grade 250 maraging steel to maintain good printability and increase the corrosion resistance. In this work, the M789 steel was manufactured by laser powder bed fusion process. The microstructural evolution of additively manufactured M789 steel was studied using optical and electron microscopy techniques. In the as-printed condition, the epitaxial grain growth with cellular dendritic structure was detected. The primary dendrite arm spacing was measured to be 0.42 ± 0.12 μm, suggesting the cooling rate is in order of 106 °C/s during solidification. This high cooling rate eliminates the occurrence of precipitation. The electron backscatter diffraction maps indicate the formation of elongated columnar grains with significant low-angle grain boundaries. After solution annealing and aging treatment, large needle-like martensitic structures were observed with fewer LAGBs than the as-printed condition. Spherical ETA-Ni3(Ti,Al) precipitates (η-phase) were formed during the heat treatment, leading to a significant increase in hardness, tensile strength, and yield strength compared to the as-printed condition. The tensile strength and yield strength along the building direction are 1798 ± 4 and 1714 ± 13 MPa, respectively. However, the elongation and toughness in the heat-treated condition are lower than that of the as-printed condition. Thermodynamic and mechanical properties simulations were also carried out, and the results are consistent with the experimental data.

Investigation of the 12 orientations variants of nanoscale Al precipitates in eutectic Si of Al-7Si-0.6Mg alloy

Various orientations and diffraction patterns from nanoscale Al precipitates in eutectic Si were investigated by high-resolution transmission electron microscopy combined with transition matrix and stereographic projection. It was found that the Al precipitates had 12 variants, all orientation relationships can be expressed as: (001)Al//{111}Si, [110]Al//<1¯10>Si. Further, a new diffraction pattern model from Al precipitates was established under [111]Si zone axis, which was in good agreement with the experiment data. The microstructure, adhesion strength and electronic structure of the interface between Al precipitate and Si matrix were studied by first-principles calculation and experimental observation. The results show that the covalent bonds are formed between interfacial Al and Si atoms, which play a key role in interfacial bind strength. Based on the Griffith fracture theory, the cracks tend to form and expand in the interior of Al precipitates firstly, and the interfaces can act as a protective layer to prevent crack propagation. Therefore, the nanoscale Al precipitates will improve the toughness of eutectic Si particles by releasing part of stress through lattice distortion. In addition, the stretched nanoscale Al precipitates can act as effective heterogeneous nucleation sites for high density deformation nanotwins in eutectic Si during deformation, which significantly improved the deformability of eutectic Si.