The effects of lanthanum on microstructure and electrochemical properties of Al–Zn–In based sacrificial anode alloys

In order to improve the non-uniform corrosion of Al–0.5Zn–0.03In–1Mg–0.05Ti alloys, Al–5Zn–0.03In–1Mg–0.05Ti–xLa (x = 0.3, 0.5 and 0.7 wt.%) alloys were developed. Microstructures and electrochemical properties of the alloys were investigated. The results show that the optimal microstructures and electrochemical properties are obtained in Al–5Zn–0.03In–1Mg–0.05Ti–0.5La alloy. The main precipitate phase is Al₂LaZn₂ particles. The excellent electrochemical properties of Al–5Zn–0.03In–1Mg–0.05Ti–0.5La alloy is mainly attributed to fine grains and grain boundaries containing fine Al₂LaZn₂ precipitates. At the same time the fine grains can improve the non-uniform corrosion of Al–0.5Zn–0.03In–1Mg–0.05Ti alloy.     

Effect of manganese on the microstructure of Mg–3Al alloy

The effect of manganese on the microstructure of Mg–3Al alloy, especially the nucleation efficiency of Al–Mn particles on primary Mg, has been investigated in this paper. Mg–0.72Mn was used to fabricate Mg–3Al–xMn (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys, and the grain sizes of these alloys fluctuate at 390 μm indicating addition of manganese does not evidently influence the grain size of Mg–3Al alloy. Through XRD, FESEM and TEM detection, it is found that Al_0.89Mn_1.11 compound is the dominant Al–Mn phase in Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, and distributes in primary Mg matrix and interdendritic regions with an angular blocky morphology. The number of Al_0.89Mn_1.11 increases gradually with increasing manganese content while the grain sizes of primary Mg are nearly the same in Mg–3Al, Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, indicating Al_0.89Mn_1.11 has low nucleation efficiency on primary Mg.     

A novel Al–Ti–B alloy for grain refining Al–Si foundry alloys

Al–Ti–B refiners with excess-Ti (Ti:B > 2.2) perform adequately for wrought aluminium alloys but they are not as efficient in the case of foundry alloys. Silicon, which is abundant in the latter, forms silicides with Ti and severely impairs the potency of TiB₂ and Al₃Ti particles. Hence, Al–Ti–B alloys with excess-B (Ti:B < 2.2) and binary Al–B alloys are favored to grain refine hypoeutectic Al–Si alloys. These grain refiners rely on the insoluble (Al,Ti)B₂ or AlB₂ particles for grain refinement, and thus do not enjoy the growth restriction provided by solute Ti. It would be very attractive to produce excess-B Al–Ti–B alloys which additionally contain Al₃Ti particles to maximize their grain refining efficiency for aluminium foundry alloys. A powder metallurgy process was employed to produce an experimental Al–3Ti–3B grain refiner which contains both the insoluble AlB₂ and the soluble Al₃Ti particles. Inoculation of a hypoeutectic Al–Si foundry alloy with this grain refiner has produced a fine equiaxed grain structure across the entire section of the test sample which was more or less retained for holding times up to 15 min.     

The phase equilibria of the Al–Ce–Ni system at 500 °C

The phase equilibria at 500 °C in the Al–Ce–Ni system in the composition region of 0–33.3 at.% Ce are investigated using XRD and SEM/EDX techniques applied to equilibrated alloys. The previously reported ternary phases and the variation of the lattice parameters versus the composition for different solid solution phases are investigated. It is confirmed that τ₂(Al₂CeNi) exists at 500 °C, while τ₃(Al₅Ce₂Ni₅) does not exist at 500 °C. A new compound τ₉ with composition of about Al₃₅Ce_16.5Ni_48.5 is found. The solubility of Ni in Al₁₁Ce₃ and αAl₃Ce is generally about 1 at.%, while the solubility of Ni in Al₂Ce is measured to be 2.7 at.%. The solubility of Ce in Al₃Ni, Al₃Ni₂, AlNi and AlNi₃ is all less than 1 at.%. The solubility of Al in CeNi₅, Ce₂Ni₇ and CeNi₃ is measured to be 30.4, 4.8 and 9.2 at.%, respectively, while there is no detectable solubility for Al in CeNi₂. A revised isothermal section at 500 °C in the Al–Ce–Ni system has been presented.     

Effect of strontium on the grain refining efficiency of Mg–3Al alloy refined by carbon inoculation

The effect of Sr on the grain refining efficiency of the Mg–3Al alloy refined by carbon inoculation has been investigated in the present study. A significant grain refinement was obtained for the Mg–3Al alloy treated with either 0.2% C or 0.2% Sr. The Al–C–O particles were found in the sample refined by 0.2% C, and the element O should come from reaction between Al₄C₃ nuclei of Mg grains and water during the process of sample preparation. The grain size of the sample refined by carbon inoculation was further decreased after the combined addition of Sr. The grain size decreased with increasing Sr content. Much higher refining efficiency was obtained when the Sr addition was increased to 0.5%. Sr is an effective element to improve the grain refining efficiency for the Mg–Al alloys refined by carbon inoculation. The number of Al₄C₃ particles in the sample refined by the combination of carbon and Sr was more than that in the sample refined by only carbon. No Al–C–O–Sr-rich particles were obviously found in the sample refined by the combination of carbon and a little (<0.5%) Sr addition.     

Al–Ti–B grain refiners via powder metallurgy processing of Al/K2TiF6/KBF4 powder blends

The response to thermal exposure of ball-milled Al/K₂TiF₆/KBF₄ powder blends was investigated to explore the potential of PM processing for the manufacture of Al–Ti–B alloys. K₂TiF₆ starts to be reduced by aluminium as early as 220 °C when ball-milled Al/K₂TiF₆/KBF₄ powder blends are heated. The reaction of KBF₄ with aluminium follows soon after. The Ti and B thus produced are both solutionized in aluminium before precipitating out as Al₃Ti and TiB₂. All these reactions take place below the melting point of aluminium. The ball-milled Al/K₂TiF₆/KBF₄ powder blends heat treated at approximately 525 °C can be compacted to produce Al–Ti–B pellets with in situ formed Al₃Ti and TiB₂ particles. These pellets are shown to be adequate grain refiners for aluminium alloys.     

Phase equilibria on Ni–Al interface under low oxygen pressure

Seventeen phases of the Ni–Al–O system at high temperatures were analyzed using thermodynamic calculations. An Ni–Al–O isothermal stability diagram was obtained from the thermochemical data. The diagram describes the interface equations for Ni/Al intermetallic compounds, Al/Al₂O₃, and Al₂O₃/Al_XNi_Y compounds, and their corresponding regions. Four univariant equilibria points and ten bivariant equilibria lines below 1126 K were obtained. The equations for the coexistence points and interface lines were also obtained. A three-domain diagram of Ni–Al–O phase arrangement at temperatures between 900 and 1191 K is shown. Thermodynamic calculations confirmed that the formation of nickel aluminate spinel (NiAl₂O₄) requires a threshold NiO activity (log a_NiO = −205.3/T − 0.347) and the partial pressure of oxygen (log P_O2=−24622/T+8 atm). In the Ni–Al–O system, a_NiO < 0.266 at 900 K, the compounds in the Ni/Al interface are formed in the order Al₃Ni_(s) → Al₃Ni_2(s) → AlNi_(s) → AlNi_3(s) → Al₂O_3(α). When a_NiO < 0.351 at 1911 K, the compounds in the Ni/Al interface are formed in the order AlNi_(s) → Al₂O_3(α).     

Identification of σ and Ω phases in AA2009/SiC composites

The microstructure evolution during ageing treatment at 170 and 190 °C of AA2009/SiC composites, reinforced with 15 vol.% particulates and whiskers, was studied by transmission electron microscopy. Besides θ′ and S′ phases, the typical hardening precipitates on Al–Cu–Mg alloys, it was found the presence of Ω and σ (Al₅Cu₆Mg₂) phases in the matrix. σ phase was only found in the matrix of particulate composite, while Ω phase appeared in both. This phase has not been previously observed in Al matrix composites based on conventional Al–Cu–Mg alloys.     

In situ XRD studies on Al–Ni and Al–Ni–Sr alloys prepared by rapid solidification

In this paper the structure and stability of Al–17 wt.%Ni(Al–17Ni) and Al–17 wt.%Ni–2 wt.%Sr alloys prepared by rapid solidification was investigated by means of XRD techniques. Our work demonstrates that both alloys are crystalline and composed of fcc (Al–Ni) solid solution and orthorhombic Al₃Ni phases. The ternary alloy shows in addition the presence of small amount of tetragonal Al₄Sr phase. In situ XRD experiment demonstrates the stability of the solute solution up to 650 °C, Al₃Ni above 750 °C while Al₄Sr overcomes melting of the major phases at 800 °C. High-temperature structure analysis proved strong bindings between Al and Ni atoms in Al₃Ni phase, corroborating its covalent nature, linear and faster increase of the fcc volume with annealing temperature. The linear correlation between constituting atoms decreases with increase of the temperature.The work also documents the applicability of pair distribution function (PDF) analysis to the study of multiphase crystalline systems.     

Al–Ti–C–Sr master alloy—A melt inoculant for simultaneous grain refinement and modification of hypoeutectic Al–Si alloys

Present article is focused on the microstructural features of Al–Ti–C–Sr master alloy, an inoculant for simultaneous grain refinement and modification of hypoeutectic Al–Si alloys. This master alloy is basically a metal matrix composite consisting of TiC and Al₄Sr phases formed in situ in the Al-matrix. TiC particles initiate the refinement of primary α-Al through heterogeneous nucleation in molten hypoeutectic Al–Si alloy, while Al₄Sr phase dissolves in molten Al–7Si alloy enriching the melt with Sr, which eventually leads to modification of eutectic silicon during solidification of the Al–7Si alloy casting. Thus present master alloy serves in both ways, as a grain refiner and a modifier for hypoeutectic Al–Si alloys.     

The Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system

Following up on recent studies of the isothermal section of the Zn–Fe–Ni, Zn–Fe–Bi and Zn–Bi–Ni ternary systems at 450 °C, the Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system with the Zn being fixed at 93 at.% was determined experimentally using the equilibrated alloys approach. The specimens were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It was found there exist 4 two-phase regions, 5 three-phase regions and 2 four-phase regions. Two liquid L (Zn) and L (Bi) can coexist with T, ζ and δ-Ni in this isothermal section, no new phase was found in this study.     

Thermodynamic modeling of the Al–Cr system

By means of calculation of phase diagram (CALPHAD) technique, the Al–Cr system was critically assessed. Three solution phases (liquid, body-centered cubic, face-centered cubic) were modeled with the Redlich–Kister equation. The intermetallic compounds Al₇Cr, Al₁₁Cr₂, Al₄Cr, Al₈Cr₅, AlCr₂, which have a homogeneity range, were treated as the formulae Al₇(Al,Cr), Al₁₁(Al,Cr)₂, Al₄(Al,Cr), (Al,Cr)₈(Al,Cr)₅, (Al,Cr)(Al,Cr)₂ using two-sublattice model, respectively. A set of self-consistent thermodynamic parameters describing the Gibbs energy of each individual phase as a function of composition and temperature for the Al–Cr system was obtained.     

Improvement of corrosion resistance of AZ91D magnesium alloy by holmium addition

The corrosion behaviour of two Mg–9Al–Ho alloys (Mg–9Al–0.24Ho and Mg–9Al–0.44Ho) was evaluated by general corrosion measurements and electrochemical methods in 3.5% NaCl solution saturated with Mg(OH)₂. The experimental results were compared with that of Mg–9Al alloy without Ho addition. Various corrosion rate tests showed that the addition of Ho obviously enhanced corrosion resistance of Mg–9Al alloy. The microstructure of the three magnesium alloys and the morphology of their corrosion product film were examined by Electron Probe Microanalysis (EPMA) and Energy Dispersion Spectroscopy (EDS). The alloys with Ho addition showed a microstructure characterized by α phase solid solution, which was surrounded by some β phase and grain-like Ho-containing phase. The improvement of corrosion resistance of the Mg–9Al–Ho alloys could be explained by the fact that the deposited Ho-containing phases were less cathodic. Moreover, the corrosion product films on the Ho-containing alloy surface demonstrated their ability to restrain further corrosion.     

Constitution of the high-Al region of Al–Cu–Rh

Phase equilibria between 540 and 1010 °C were studied in Al–Cu–Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al₅Rh₂ (C-phase) dissolves up to 13 at.% Cu, “Al₃Rh” (₆-phase) up to 15 at.% Cu and Al₉Rh₂ up to 1.5 at.% Cu. The solubility of the third element in other binary Al–Rh and Al–Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fcc C₂-phase structurally related to the C-phase is formed. Stable decagonal phase (D₁-phase) is formed below 1005 °C in a compositional range extending from Al₆₅Cu₁₆Rh₁₉ to Al₆₂Cu₂₃Rh₁₅, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al₇₀Cu₂₀Rh₁₀ composition below 660 °C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 °C isothermal sections were determined.     

A contribution to the Al–Pd–Mn phase diagram

A part of the Al–Pd–Mn phase diagram in the vicinity of the icosahedral phase was refined. Partial isothermal sections of 710, 850, 870 and 880°C are presented. The overall compositional range of the icosahedral phase was found to be between 5.8 and 10.5 at.% Mn and between 69.5 and 71.5 at.% Al at these temperatures. It shifts to lower Mn concentration at lower temperatures. It was confirmed that the phase usually designated Al₃Pd has a lower Al concentration in the binary alloys than that according to the formula. It extends to the ternary compositions up to about 5 at.% Mn. The increase of the Mn content results in an increase of the Al concentration of this phase.     

Constitution and hardnesses of the Al–Ir system

The Al–Ir phase diagram was investigated using optical and scanning electron microscopy, and X-ray diffraction. The results were found to agree with published literature, with the exception of the congruent melting of Al_2.7Ir and a previously unreported eutectic reaction to form Al_2.7Ir and AlIr. The AlIr and Al_2.7Ir phases had the widest composition ranges: 47–53 and 23–30 at.% Ir respectively.Mechanical tests, in the form of Vickers hardness tests were used to deduce the fracture toughness of the alloys. It was found that the high Al-content intermetallic compounds were very brittle, and the alloys containing AlIr were tougher. This compound was tougher on the Ir-rich side, especially when there was a small amount of the AlIr+(Ir) eutectic between the AlIr dendrites.     

Development of ultrafine grained Al–Mg–Si alloy with enhanced strength and ductility

The microstructure and mechanical properties of a precipitation hardenable Al–Mg–Si alloy subjected to cryorolling (CR), short annealing and ageing treatments are reported in this present work. The pre-cryorolled solid solution treatment combined with post-CR short annealing (155 °C for 5 min) and then ageing treatment (125 °C for 12 h) has been found to be the optimum processing condition to obtain the ultrafine grained microstructure with substantial improvement of tensile strength (286 MPa) and good tensile ductility (14%) in the Al–Mg–Si alloy. The significant improvement of the mechanical properties of the cryorolled and peak aged 6063 Al alloys have been observed as compared to its bulk alloys in the peak-aged condition (T6).     

Effect of aluminum content on mechanical properties of hydrogenated Mg–Al magnesium alloys

The mechanical properties of hydrogenated Mg–Al magnesium alloys with various aluminum content were investigated. The ductility, yield strength (YS) and ultimate tensile strength (UTS) of the hydrogenated material decreased while the hardness increased with increasing the aluminum content. Microscopic observations of cross-sections of hydrogenated specimens with various Al content revealed that hydrogen cracks extended deeply as the Al content in the Mg–Al alloys increased. Moreover, X-ray diffraction (XRD) analysis revealed that MgH₂ and AlH₃ hydrides are formed during hydrogenation and were found to contribute to hydrogen embrittlement of Mg–Al alloys. However, the embrittled zone was observed to be larger at the fracture surface of Mg–15Al alloy than that of Mg–5Al alloy. Moreover, the fracture surface of Mg–30Al alloy exhibited completely brittle fracture after hydrogenation.     

Age hardening phenomena of rapidly quenched non-combustible Mg−Al−Si−Ca and Mg−Zn−Ca alloys

Non-combustible Mg−Al−Si and Mg−Zn base alloys containing Ca were rapidly quenched via melt spinning. The melt-spun ribbons were aged, and then the effects of additional elements on age hardening behavior and microstructural change were investigated. Age hardening occurred after aging at 200°C in the Mg−Al−Si−Ca alloys mainly due to the formation of Al₂Ca or Mg₂Ca phases, whereas it occurred in the Mg−Zn−Ca alloys mostly due to the distribution of Mg₆Ca₂Zn₃ and Mg₂Ca. With the increase of Ca content, the hardness values of the aged ribbons were increased. In this study, Mg−6Zn−5Ca alloy showed the maximum peak hardness after aging at 200°C for 1 hour. On the contrary, Mg−xZn−1.5Ca alloys couldn't show the pronounced peak hardness because of low Ca content.     

Electrochemical behaviour and corrosion performance of Mg–Li–Al–Zn anodes with high Al composition

This study investigated the electrochemical and corrosion performance of Mg–Li–Al–Zn anodes with Al compositions of 3 wt.% and 9 wt.%. Mg–Li–Al–Zn alloy with 9 wt.% Al had a relatively negative open-circuit potential and a high discharge voltage in MgCl₂ electrolyte, owing to the distribution of numerous AlLi particles in the matrix of the alloy. AlLi particles were believed to transform to Al particles during the corrosion of the Mg–Li–Al–Zn anode. The high-Al anode material exhibited good corrosion performance since a dense and continuous Mg(OH)₂/Al composite layer covered the surface of the high-Al anode. Experimentally, increasing the Li⁺ concentration in the electrolyte improved the corrosion performance of the Mg anode.