Al Precipitation Research Articles

Effect of microstructure on Ti3Al precipitation during ageing of Ti-6Al-4V alloy

The aim of the present work is to explore the age-hardening potential of Ti-6Al-4V (Ti-64) alloy with variation of the starting microstructure, with attention to the precipitation of nano-sized Ti3Al phase, as influenced by microstructural features. The alloy was either solution-treated or deformed by compression at temperatures above and below its β-transus to produce microstructures comprising martensitic, lamellar and globular α morphologies, as well as the existence or absence of β phase, and subsequently submitted to ageing treatments at 400°C/8h using in situ x-ray diffraction. Precipitated fractions of Ti3Al were obtained via Rietveld refinement and aged microstructures were characterized by micro-hardness measurements. Results show that α2 precipitation is favored by a globular morphology of α and hindered by a martensitic α morphology, and suggest that the presence of β phase also has as influence on precipitation.

Interface Formation and Characterization of Brass/Aluminum Compounds Fabricated Through Die Casting and Semi-Continuous Casting

An innovative method based on the static and semi-continuous casting technology is investigated for the production of bilayer brass/aluminum billets and rods. The paper focuses on the interface formation and characterization of metallurgically bonded hybrids consisting of brass CuZn37 and the aluminum alloys AA5083, AA6060 and AA7075. Depending on the thermal process conditions, the interfacial reaction zone between the joining partners exhibits a thickness between a few micrometers and a few millimeters. Regardless of the usage of disparate aluminum alloys, the interface of as-cast brass/aluminum compounds is characterized by four intermetallic layers, namely CuZn $$(\hbox {CuZn-}\upbeta )$$, $$\hbox {Al}_3\hbox {Cu}_5\hbox {Zn}_2$$, $$\hbox {Al}_4\hbox {Cu}_3\hbox {Zn}$$ and AlCu $$(\hbox {AlCu-}\upeta _2)$$, as well as an anomalous eutectic area of aluminum solid solution $$(\upalpha \hbox {-Al})$$, $$\hbox {Al}_2\hbox {Cu}$$$$(\hbox {AlCu-}\uptheta )$$ and eutectic structures. The intermetallic layers are primarily formed by solid-state diffusion, whereas the anomalous eutectic zone is a result of dissolution of Cu in liquid Al and subsequent solidification and precipitation. The microhardness, elastomechanical properties and the bonding strength of the interfacial area of as-cast compounds are determined using the nanoindentation and push-out testing technique. Due to the high cooling rates, brass/aluminum compounds fabricated through semi-continuous casting are characterized by a sufficient geometrical stability of the interface and high bonding quality.

Long-term effects of liming on soil physico-chemical properties and micro-arthropod communities in Scotch pine forest

We tested the long-term effects of liming on soil micro-arthropods in a stand of Scotch pine on former drift sand in the Netherlands. To counteract the effects of acidification, liming was applied in increasing quantities from 0 (control), 3, 6, 9 and 18 ton ha−1 on experimental plots over the course of 1985 and 1986. Soil samples for chemical analyses and those for extraction of soil micro-arthropods were taken in October 2017, 32 years after application. Liming did restore the buffer capacity of the soil and did increase pH and increased plant biomass of the understory. Liming, however, also created P limitation, due to Al precipitation and an excess of free Ca to bind on. The consequence of the observed P limitation was a significant decrease in herbivorous and herbofungivorous micro-arthropods, whereas fungivorous and opportunistic herbofungivores were unaffected. P availability in acidified soils had become limited, due to higher N input that also caused acidification and due to remediation with added buffer material. Decomposition of organic matter was accelerated and increased N release to the system. The forest ecosystem had become P limited, where it originally was N limited or N and P co-limited.

Microstructure, mechanical properties and superplasticity of the Al–Cu–Y–Zr alloy

The phase composition, mechanical properties, and superplastic deformation behavior of a novel Al-4.7Cu-1.6Y-0.3Zr alloy were analyzed. The precipitation of Al3(Zr,Y) dispersoids was observed during a homogenization treatment. The precipitates have an L12 structure and a mean size of 17 and 19 nm at 540 and 590 °C, respectively. The sheets exhibit a yield strength of 292 MPa, an ultimate tensile strength of 320 MPa, and an elongation of 5.3% after simple thermomechanical treatment and annealing at 100 °C. The Al-4.7Cu-1.6Y-0.3Zr alloy exhibits superplasticity with m > 0.4 and elongation of 300–400% within a temperature range of 550–580 °C and a strain rate range of 1 × 10−4 to 1 × 10−3 s−1.

Improving coarsening resistance of dilute Al-Sc-Zr-Si alloys with Sr or Zn additions

We study the effect of a small addition of Zn (0.5 at.%) or a micro-addition of Sr (0.005 at.%) to a dilute Al-0.05Sc-0.07Zr-0.02Si (at.%) on precipitation of Al3(Sc,Zr) nanoprecipitates. Upon aging at 400 °C, both the Zn- and Sr-modified alloys retain peak-aged hardness (600 ± 10 MPa) for at least two weeks, while the Zn/Sr-free control alloy shows lower peak hardness (475 ± 8 MPa), which starts dropping after only 3 days. Similarly, peak hardness values achieved at 475 °C during isochronal aging, are much higher for the Zn/Sr-modified alloy (610 ± 10 and 590 ± 14 MPa) than for the Zn/Sr-free alloy (480 ± 5 MPa). Local electrode atom probe tomography shows that Sr and Zn atoms segregate to the Al3(Sc,Zr) nanoprecipitates: up to 0.1 at. % for Sr, and up to 1.1 at.% for Zn, with a peak of ∼5 at.% at the interface with the matrix. This may affect their coarsening rate by (i) reducing the diffusivity of Sc and Zr in the matrix and (ii) altering the precipitate/matrix interfacial energy. In the peak-aged condition, the Zn-modified alloy has the same creep resistance at 300 °C than the Zn-free control alloy, but its higher overaging resistance allows for longer creep operating times.

Synthesis and characterization of magnetic nanoparticles from raffinate of industrial copper solvent extraction plants

Abstract Magnetite nanoparticles successfully produced from the raffinate of an Iranian industrial copper solvent extraction unit. Removal of iron from leach solution is important for successful operation of hydrometallurgical recovery of copper. It includes reduction of Fe3+ to Fe2+ followed by precipitation of Al3+ as Al(OH)3, oxidation of Fe2+ to Fe3+ (the theoretical ratio for stoichiometric, Fe3+/Fe2+ = 2) and finally synthesize of nano-sized magnetite. Two different Fe2+ oxidation agents namely H2O2 and O2 were used. Using XRD, FTIR, FESEM, and TEM analysis, the phase structure, morphology, and size distribution of magnetic nanoparticles, produced under different conditions, were evaluated and compared. Under optimum conditions spherical magnetic nanoparticles with an average size of about 25 ± 3 nm can be produced. The XRD analysis of produced nanoparticles after purification of raffinate showed the slight formation of aluminum hydroxide, goethite and hematite phases. In addition, the VSM results indicate the highly ferromagnetic behavior for samples at the room temperature with a saturation magnetization of 41.25 emu/g.

Effects of Al3+ precipitation onto primitive amorphous Cu-Zn precipitate on methanol synthesis over Cu/ZnO/Al2O3 catalyst

The phase of Cu,Zn,Al precursors strongly affects the activity of their final catalysts. Herein, the Cu,Zn,Al precursor was prepared by precipitation of Al3+ onto primitive, amorphous Cu,Zn precipitate. This precursor turned out to be a phase mixture of zincian malachite and hydrotalcite in which the latter phase was less abundant compared to the co-precipitated precursor. The final catalyst derived from this precursor exhibited a little higher copper surface area and methanol synthesis activity than the co-precipitated counterpart. Therefore, the two precursor phases need to be mixed in an adequate proportion for the preparation of active Cu/ZnO/Al2O3 catalyst.

Effect of Homogenization Treatment on Superplastic Properties of Aluminum Based Alloy with Minor Zr and Sc Additions

Effect of one-step and two-step homogenization treatment on precipitation of Al3(Sc,Zr) dispersoids, grain structure after annealing of cold rolled sheets and superplastic behaviour of a novel Al-Mg based alloy were studied. Heterogeneous nucleation of Al3(Sc,Zr) phase on dislocations and subboundaries dominated at one-step annealing and both homogeneous and heterogeneous nucleation of Al3(Sc,Zr) were observed at two-step annealing modes. It was shown that two-step treatment mode provides high density of Al3(Sc,Zr) precipitates and 650 % of elongation at the constant strain rate of 10-2 s-1 in the studied alloy.

Understanding the Strategies to Overcome Phosphorus-Deficiency and Aluminum-Toxicity by Ryegrass Endophytic and Rhizosphere Phosphobacteria.

Phosphobacteria, secreting organic acids and phosphatases, usually favor plant performance in acidic soils by increasing phosphorus (P) availability and aluminum (Al) complexing. However, it is not well-known how P-deficiency and Al-toxicity affect the phosphobacteria physiology. Since P and Al problems often co-occur in acidic soils, we have therefore proposed the evaluation of the single and combined effects of P-deficiency and Al-toxicity on growth, organic acids secretion, malate dehydrogenase (mdh) gene expression, and phosphatase activity of five Al-tolerant phosphobacteria previously isolated from ryegrass. These phosphobacteria were identified as Klebsiella sp. RC3, Stenotrophomona sp. RC5, Klebsiella sp. RCJ4, Serratia sp. RCJ6, and Enterobacter sp. RJAL6. The strains were cultivated in mineral media modified to obtain (i) high P in absence of Al–toxicity, (ii) high P in presence of Al–toxicity, (iii) low P in absence of Al–toxicity, and (iv) low P in presence of Al–toxicity. High and low P were obtained by adding KH2PO4 at final concentration of 1.4 and 0.05 mM, respectively. To avoid Al precipitation, AlCl3 × 6H2O was previously complexed to citric acid (sole carbon source) in concentrations of 10 mM. The secreted organic acids were identified and quantified by HPLC, relative mdh gene expression was determined by qRT-PCR and phosphatase activity was colorimetrically determined using p-nitrophenyl phosphate as substrate. Our results revealed that although a higher secretion of all organic acids was achieved under P–deficiency, the patterns of organic acids secretion were variable and dependent on treatment and strain. The organic acid secretion is exacerbated when Al was added into media, particularly in the form of malic and citric acid. The mdh gene expression was significantly up–regulated by the strains RC3, RC5, and RCJ6 under P–deficiency and Al–toxicity. In general, Al–tolerant phosphobacteria under P deficiency increased both acid and alkaline phosphatase activity with respect to the control, which was deepened when Al was present. The knowledge of this bacterial behavior in vitro is important to understand and predict the behavior of phosphobacteria in vivo. This knowledge is essential to generate smart and efficient biofertilizers, based in Al–tolerant phosphobacteria which could be expansively used in acidic soils.

Freshwater ecotoxicity characterization factors for aluminum

Aluminum (Al) is an abundant, non-essential element with complex geochemistry and aquatic toxicity. Considering its complex environmental behavior is critical for providing a reasonable estimate of its potential freshwater aquatic ecotoxicity in the context of Life Cycle Impact Assessment (LCIA). Al characterization factors (CFs) are calculated using the following: (1) USEtox™ model version 2.1 for environmental fate, (2) MINEQL+ to estimate the distribution of Al between the solid phase precipitate and total dissolved Al, (3) WHAM 7 for Al speciation within the total dissolved phase, and (4) Biotic Ligand Model (BLM) and Free Ion Activity Model (FIAM) for ecotoxicity estimation for seven freshwater archetypes and default landscape properties for the European continent. The sensitivity of the CFs to aquatic chemistry parameters is calculated. New CFs are compared with Dong et al. (Chemosphere 112:26–33, 2014) and default CF calculated by USEtox 2.1. Al CFs vary over 5 orders of magnitude between the seven archetypes, with an arithmetic average CFave of 0.04 eq 1,4-DCB (recommended for use), geometric mean CFgeo of 0.0014 eq 1,4-DCB, and weighted average CFwt of 0.026 eq 1,4-DCB. These values are lower (less toxic) than those for Cu, Ni, Zn, and Pb (with one exception). The effect factor (EF) contributed most to this variability followed by the bioavailability factor (BF), varying over 8 and 4 orders of magnitude, respectively. These revised CFs are 2–6 orders of magnitude lower than those presented by Dong et al. (Chemosphere 112:26–33, 2014) mainly because of consideration of Al precipitation. Freshwater archetype-specific Al CFs for freshwater ecotoxicity that address the effect of Al speciation on bioavailability (BF) and ecotoxicity (EF) have been calculated, and a CF of 0.04 eq 1,4-DCB is recommended for use in generic LCA. For site-specific LCA, the choice of water chemistry and, in particular, pH, and consideration of metal precipitation could significantly influence results. Incorporating estimates of metal speciation and its effect on aquatic toxicity is essential when conducting LCIA. Along with metal speciation estimates, the values derived from the definition of water chemistry parameters must also be included into LCIA. For site-generic assessments, we recommend using the arithmetic average of metal CFs. We also recommend using FIAM as a suitable alternative to BLM to estimate EF if the latter is not available. Consideration of metal speciation is essential for providing more realistic estimates of Al freshwater ecotoxicity in the context of LCIA.

Indirect mineral carbonation of blast furnace slag with (NH4)2SO4 as a recyclable extractant

Large quantities of CO2 and blast furnace slag are discharged in the iron and steel industry. Mineral carbonation of blast furnace slag can offer substantial CO2 emission reduction and comprehensive utilisation of the solid waste. In this study, a recyclable extractant, (NH4)2SO4, was used to extract calcium and magnesium from blast furnace slag (main phases of gehlenite and akermanite) by using low-temperature roasting to fix CO2 through aqueous carbonation. The process parameters and efficiency of the roasting extraction, mineralisation, and Al recovery were investigated in detail. The results showed that the extractions of Ca, Mg, and Al can reach almost 100% at an (NH4)2SO4-to-slag mass ratio of 3:1 and at 370 °C in 1 h. Adjusting the pH value of the leaching solution of the roasted slag to 5.5 with the NH3 released during the roasting resulted in 99% Al precipitation, while co-precipitation of Mg was lower than 2%. The Mg-rich leachate after the depletion of Al and the leaching residue (main phases of CaSO4 and SiO2) were carbonated using (NH4)2CO3 and NH4HCO3 solutions, respectively, under mild conditions. Approximately 99% of Ca and 89% of Mg in the blast furnace slag were converted into CaCO3 and (NH4)2Mg(CO3)2•4H2O, respectively. The latter can be selectively decomposed to magnesium carbonate at 100–200 °C to recover the NH3 for reuse. In the present route, the total CO2 sequestration capacity per tonne of blast furnace slag reached up to 316 kg, and 313 kg of Al-rich precipitate, 1000 kg of carbonated product containing CaCO3 and SiO2, and 304 kg of carbonated product containing calcium carbonate and magnesium carbonate were recovered simultaneously. These products can be used, respectively, as raw materials for the production of electrolytic aluminium, cement, and light magnesium carbonate to replace natural resources.

TEM study on the microstructure of the Zn-Al-Mg alloy

The microstructure of the 95wt%Zn-2.3wt%Al-2.7wt%Mg bulk alloy used for hot-dip galvanization has been investigated by TEM and SEM. The alloy exhibits a multi-scales and multi-phases microstructure. The dendrite and the granular/lamellar region are observed at hundreds-micron scale, and each has finer details. The dendrite is composed of the coarse hcp-Zn grains, with MgZn2 grains between the branches, and some individual bulk MgZn2. The granular/lamellar region has a complex ternary eutectic morphology, containing the hcp-Zn lamellas, the monotectoid product of Al-bubble wrapping Zn-granule, and the Zn-Mg lamellas, and the dimension of every unit is less than 1μm. The hcp-Zn phase, in the form of coarse grains and lamellas, is supersaturated, with numerous platelet Al precipitation about tens of nanometers inside, with the orientation relationship of (0 0 1)Al//(0 0 0 1)Zn, and [1 1 0]Al near 112¯0Zn. The Zn-Mg lamella is a MgZn2 matrix with polygon Mg2Zn11 precipitates less than 100nm and some Mg segregations.

Evolution of microstructure and mechanical properties of A356 aluminium alloy processed by hot spinning process

The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of AlSiTi phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.

Effects of homogenization on precipitation of Al3(Er,Zr) particles and recrystallization behavior in a new type Al-Zn-Mg-Er-Zr alloy

The effects of homogenization treatments on the precipitation behavior of Al3(Er,Zr) particles and theirs effects on recrystallization resistance in a new type Al-Zn-Mg-Er-Zr alloy have been investigated. Four different homogenization treatments, conventional one-stage homogenization, double-stage homogenization and ramp heating homogenization are carried out. Compared with that in the conventional one-stage homogenization, a finer particle size, higher number density and volume fraction of Al3(Er,Zr) particles can be obtained in other three homogenization treatments. In addition, the double-stage homogenization and the ramp heating homogenization can improve the Al3(Er,Zr) particles distribution and minimize the width of precipitation free zone in the region near the grain boundary, and provide an additional but nonnegligible strengthening effect for the Al-Zn-Mg-Er-Zr alloy. The difference in precipitation behavior of Al3(Er,Zr) particles lead to different recrystallization resistance. The high recrystallization resistance can be attributed to the larger fV/r ratio of Al3(Er,Zr) particles, which resulting in a higher Zener drag to effectively resist the recrystallization in Al-Zn-Mg-Er-Zr alloy during hot deformation and the subsequent thermal processing. Therefore, under the same annealing time, the double-stage homogenized and the ramp heating homogenized samples can achieve a significant lower recrystallized fraction compared with the conventional one-stage homogenized samples.

Precipitation of ScAl<sub>3</sub> Phase during Solutionizing and Ageing of Hypoeutectic Al-Sc Alloys and its Impact to Mechanical Properties

In this paper, precipitation of ScAl3 phase during solutionizing and ageing and its impact to mechanical properties of hypoeutectic Al-Sc alloy and effect of Sc addition amount were investigated by TEM and SEM microstructure observation and mechanical property testing. During solutionizing at 640oC for 24h, for Al-0.2wt.%Sc and Al-0.4wt.%Sc alloy, ScAl3 particles formed in the course of solidification become smaller, indicating, as a whole, Sc is partially dissolved into Al solution. Simultaneously, precipitation of two types of ScAl3 particles are observed by TEM. One has a size of 200~300nm, and the other is much small, 5~20nm in size. Though re-dissolution of Sc solute into Al solution and precipitation of large and fine ScAl3 particles occur in the solutionizing course, but the strength and hardness are decreased. The key reason for it is thought to be the softening effect of high level of vacancies in matrix lattice from the high solutionizing temperature. After further aging at 300oC for 3h, a great number of fine ScAl3 particles are precipitated in the Al matrix, which leads to a considerable precipitation hardening effect, thus the strength and hardness are increased obviously. Increasing the Sc content in the alloy results in a considerable rise in as-cast and as-aged strength and hardness, due to the solution strengthening and precipitation hardening respectively.

The determining role of aluminum on copper precipitation and mechanical properties in Cu-Ni-bearing low alloy steel

We elucidate here the determining role of aluminum on the precipitation behavior and mechanical properties in Cu-Ni-bearing low alloy steel. The microstructure and precipitation behavior were studied by electron microscopy in conjunction with the thermodynamic analysis. Aluminum had significant influence on the precipitation behavior of niobium such that the precipitation temperature of Nb(C, N) was decreased, and prior austenite grain size was governed by Al and Nb precipitation. The nano-size B2 structure of particles was confirmed to be Ni(Al, Mn), and Mn atoms preferred to substitute for Al in the sublattice site in the B2 structure. Furthermore, aluminum effectively increased precipitate density by increasing the nucleation rate of ordered-B2 Ni(Al, Mn) and copper precipitation, thereby increasing the hardness of Cu-Ni-bearing low alloy steel during tempering. Excellent tensile properties were obtained in low carbon steel after quenching and tempering, with tensile strength of 1150MPa and yield strength of 1020MPa. The high strength is attributed to the martensite matrix and precipitation of copper.

Geochemistry of dissolved aluminum at low pH: Hydrobasaluminite formation and interaction with trace metals, silica and microbial cells under anoxic conditions

The precipitation of dissolved aluminum is among the most important geochemical processes affecting the water chemistry and trace metal dynamics of acid mine drainage (AMD). In this study, we focus on the in situ formation of Al precipitates and their subsequent interaction with trace metals, dissolved silica and microbial cells under anoxic conditions (e.g., deep strata of pit lakes, flooded underground mines). In the presence of sulfate (0.1–0.2M), dissolved aluminum precipitates at pH ~4.0 and forms an amorphous, globular hydroxysulfate precipitate with composition corresponding to hydrobasaluminite. This proto-hydrobasaluminite shows an important capacity to incorporate SiO2 (aq), divalent metal cations (FeII, PbII, BeII), and many anion-forming trace elements (As, Cr, Sb, V, Se, U) by coprecipitation. Removal efficiencies obtained experimentally with freshly formed hydrobasaluminite under anoxic and oxic conditions were consistent with metal profiles obtained in the pit lakes and suggest that the behaviour of many toxic metals is closely linked to the Al particles. Detailed transmission electron microscopy (TEM) shows that hydrobasaluminite may coexist with more crystalline minerals like gibbsite, bayerite and/or allophane, which are present as nanocrystals embedded in the amorphous matrix and appear to form by transformation of the former. Hydrobasaluminite precipitation is favoured by the activity of iron- and sulfate-reducing microbes in the water column and at the sediment/water interface. Our study shows that, at solubility equilibrium, microbial cells often serve as nuclei for Al precipitation. Further, chemical mapping of Al-coated cells by scanning/TEM shows an important incorporation of SiO2, Fe2+ (valence confirmed by electron energy loss spectroscopy) and other metal cations (e.g., Mg2+) in the Al cell coatings as compared to Al particles presumed to form via abiotic precipitation. These Al cell coatings are amorphous to X-rays and their compositions likely result from coprecipitation of SiO2 and Fe2+ resulting in Si-rich and Fe(II)-rich hydrobasaluminite. The disparity between field and laboratory data, the serendipitous detection of nontronite-like smectite in precipitates formed in the acidic waters under laboratory conditions, and the apparent saturation with respect to different clay minerals (e.g., kaolinite, halloysite) are all evidences suggesting thermodynamic feasibility of aluminosilicate precursor formation in these systems.

Precipitation hardening and recrystallization behavior of Al[sbnd]Mg[sbnd]Er[sbnd]Zr alloys

The precipitation hardening and recrystallization behavior of AlMgErZr alloys have been investigated. The results show that Mg solute and its concentration has negligible influence on the precipitation of Al3(ErZr). The distribution of the precipitates is inhomogeneous due to the inhomogeneous distribution of the solute species formed during solidification. The recrystallization temperatures of the alloys with addition of Er and Zr are higher than that of the alloys free of Er and Zr, especially the recrystallization end temperature of the AlMgErZr alloy which is at least 200 °C higher than that of the Al5Mg alloy due to the retardation of the precipitates. Recrystallization of AlMgErZr alloys initiates at the precipitation free zone. The recrystallization starting temperatures of the AlMgErZr alloys increase with the decrease of the Mg concentration due to high deformation energy of the AlMgErZr alloy with high Mg concentration, and the recrystallization end temperatures are close among AlMgErZr alloys with different Mg concentration.

Assessment on the Stability and Speciation of Phosphorus in River Sediments

Sediments are heterogeneous mixtures of assorted soil separates and organic matter that serve as repositories of many pollutants. This study investigated phosphorus (P) stability in river sediments as controlled by P speciation and environmental conditions, such as temperature (T), dissolved oxygen (DO), redox conditions (Eh), and pH. It attempted to evaluate the experimental conditions under which P could potentially be tied-up in river sediments. Sediment cores samples were collected from James River, in Virginia, U.S.A. near a former dairy farm and analyzed for T, pH, Eh, carbon (C) and pertinent metal ions. Results indicated that high P concentration correlated well with Fe and had non-uniform correlations with clay, Al and Ca, which changed with depth of cores. At low pH, P concentration was higher in anaerobic than aerobic sediments and aluminum (Al) precipitation was highest at low pH, which indicated Al phosphate stability in reduced (anaerobic) conditions. Above pH 7, in aerobic environments, the Minteqa2 speciation model predicted a high stability for Al-OH species. The minerals variscite, vivianite, strengite hydroxyapatite, and two forms of magnesium hydroxide species were predicted to exist in the pH ranges used in this study. Elemental P distribution assessment using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) inferred that P could be bound either to C and Al, Fe or Mn depending on their relative abundances.

Microstructure, mechanical properties and first-principle analysis of vacuum die-cast Mg–7Al alloy with Sn addition

The influences of Sn element and heat treatment on the microstructure and mechanical properties of Mg–7Al alloy prepared by vacuum die cast (VDC) were studied. The results indicate that α-Mg dendrite and Mg17Al12 are refined and new Mg2Sn phase is formed in Mg–7Al alloy with 2 wt% Sn addition. The ultimate tensile strength (σ b) of Mg–7Al alloy increases from 205 to 258 MPa (i.e., a 25 % increase). The mechanical properties of Mg–7Al–2Sn (AT72) alloy are further improved through heat treatment because of the dense microstructures processed by VDC. In particular, the mechanical properties of AT72 alloy are greatly improved after solution treatment at 400 °C for 20 h due to solution strengthening of Al and Sn elements and precipitation strengthening of Mg2Sn phases. The precipitation strengthening effect of particle Mg2Sn phases is more apparent due to the decomposition of Mg17Al12 phases. In addition, from the view of microscopic theory, the effect of Sn on mechanical properties of Mg–7Al alloy was discussed by first-principle calculation.