Microstructural properties of sintered Al–Cu–Mg–Sn alloys

A non-commercial Al4Cu0.5Mg alloy has been used for investigating the effects of the elemental Sn additions. Uniaxial die compaction response of the alloys in terms of green density was examined, and the results showed that Sn addition has no effect when compacting conducted under high pressures. In total, 93–95% green density was achieved with an applied pressure of 400 MPa. Thermal events occurring during the sintering of the emerging alloys were studied by using differential scanning calorimetry (DSC). First thermal event on the DSC analysis of the Al4Cu0.5Mg1Sn alloy is the melting of elemental Sn, whereas for Al4Cu0.5Mg alloy, it is the formation of Al–Mg liquid nearly at 450 °C. Also it is clearly seen on the DSC analysis that Sn addition led to an increase in the formation enthalpy of Al–Mg liquid phase. High Sn content and high sintering temperature (620 °C), therefore high liquid-phase content, caused decrease on the mechanical properties due to thick intergranular phases and grain coarsening. Highest transverse rupture strength and hardness values were obtained from Al4Cu0.5Mg0.1Sn alloy sintered at 600 °C and measured as 390 MPa and 73 HB, respectively.     

Nano-scale dissolution phenomena in Al–Cu–Mg alloys

Localized corrosion of aluminum alloys is a major issue worldwide and in spite of decades of work, several questions still remain unresolved. In this study we focus on key issues in the context of localized corrosion of Al–Cu–Mg/Al–Mg–Cu alloys that have not been adequately addressed. By careful electrochemical exposure along with high-resolution electron microscopy, we reveal that microstructural features down to a few nanometers in size can behave as unique electrochemical entities. In addition, not only is this critical to emerging damage accumulation models, but we also reveal that significant dissolution can occur at potentials below the breakdown potential of the bulk alloy. This work has potentially wide consequences in the interpretation of Al alloy corrosion and alloys design for corrosion resistance.     

Experimental investigation of the Nd–Al–Si system

The isothermal section of the Nd–Al–Si ternary system at 500 °C has been investigated using differential thermal analysis, X-ray diffraction analysis, scanning electron microscopy and electron micro-probe analysis. Four ternary intermetallic compounds were confirmed: NdAl₂Si₂ (τ₁), hP5-CaLa₂O₂ structure type, Nd₂Al₃Si (τ₂), hP3-AlB₂ structure type, NdAl_1−x Si_1+x , 0.25 ≤ x ≤ 0.3 (τ₃), tI12-αThSi₂ structure type and Nd₂Al_1−x Si_1+x , 0 ≤ x ≤ 0.2, (τ₅), oS8-CrB structure type. A new ternary intermetallic phase (τ₄) was found: Nd₄Al₃Si₃, orthorhombic oS20, isotypic with Pr₄Al₃Ge₃.     

Thermal analysis of W-free Co–(Ni)–Al–Mo–Nb superalloys

CuAl layered double hydroxide (CuAl-LDH) was synthesized by co-precipitation. Sodium phenyl phosphate (SPP) and sodium dodecyl sulfate (SDS) are used to modify CuAl-LDH for preparing CuAl-(SPP)LDH and CuAl-(SDS)LDH, which were incorporated into epoxy resin (EP) to obtain EP/CuAl-(SPP)LDH and EP/CuAl-(SPP)LDH nanocomposites. The results indicate that SPP and SDS are intercalated into the interlayers of CuAl-LDH, and CuAl-(SPP)LDH has larger layer spacing than CuAl-(SDS)LDH. The thermal stability and flame-retardant performances of EP/CuAl-(SPP)LDH nanocomposites were better than those of EP/CuAl-(SDS)LDH composites. Compared with those of EP/4CuAl-(SDS)LDH nanocomposites, the peak heat release rate (PHRR) of EP/4CuAl-(SPP)LDH nanocomposites is reduced 25.8% and 55.6%, and peak smoke production rate (PSPR) value of EP/4CuAl-(SPP)LDH nanocomposites is reduced 27.6% and 46.2%, value of EP/4CuAl-(SPP)LDH nanocomposites is reduced 27.6% and 46.2%, respectively. The improved flame retardancy and smoke suppression performances of EP/CuAl-(SPP)LDH nanocomposites were attributed to the combination of copper compounds and SPP, promoting the formation of swollen, continuous and compact char layers on the surface of EP nanocomposites during combustion, eventually restraining the decomposition of EP nanocomposites.

     

Synthesis of quasi-crystalline phases in the Al–Cu–Fe–Cr system

Phase equilibria in the Al–Cu–Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i ? d phase transitions in alloys Al₆₅Cu₂₅Fe₅Cr₅ and Al₇₀Cu₂₀Fe₅Cr₅. In the Al–Cu–Fe–Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.     

Liquid–liquid phase equilibrium in ternary immiscible Al–Bi–Sn melts

In this paper, the liquid-phase separation of ternary immiscible Al–Bi–Sn melts was studied with resistivity and thermal analysis methods at different temperatures. The resistivity–temperature curves appear anomalous and abrupt change as rising temperature, corresponding to the distinctive and low peak of melting process in the differential scanning calorimetry (DSC) curves, indicative of the occurrence of the liquid-phase separation. The anomalous behaviour of the resistivity temperature dependence is attributable to concentration–concentration fluctuations. The microheterogeneity–microhomogeneity transformation causes large fluctuations in concentration, which make the randomness and chaos of the atoms larger, leading to the greater impediment to electron movement and the sharp rise of resistivity. The addition of tin to the Al–Bi immiscible alloys decreases the monotectic reaction. It is concluded that concentration–concentration fluctuations are responsible for the anomalous behaviour of resistivity and DSC methods.     

Effect of cooling rate and Al content on solidification behavior and microstructure evolution of as-cast Mg–Al–Ca–Sm alloys

Journal of Thermal Analysis and Calorimetry - In the present study, the Mg–xAl–2Ca–2Sm (x = 3, 5, 9 and 15) alloys were fabricated in sand mold with stepped type, and...     

Cooling curve thermal analysis of Al–Mg2Si–Cu–xSr composite

Journal of Thermal Analysis and Calorimetry - In situ composites are today being considered for industrial use, owing to the fewer production steps involved, lower production cost, and better...     

Calorimetric study of spinodal decomposition in β-Cu–Al–Mn

Journal of Thermal Analysis and Calorimetry - We report data obtained from the spinodal decomposition in samples of two compositions of intermetallic Cu–Al–Mn shape memory alloys....     

Phase transformations in an annealed Cu–9Al–10Mn–3Gd alloy

The phase transformations in the Cu–9Al–10Mn–3Gd alloy were studied using differential scanning calorimetry, X-ray diffraction patterns, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field and temperature. The results showed that the effects produced by the Mn atoms are dominant on those attributed to the Gd atoms in the annealed Cu–9Al–10Mn–3Gd alloy. For quaternary alloy the results also indicated that the Gd stabilizes a fraction of the paramagnetic β₃ phase at lower temperatures and suppresses its paramagnetic–ferromagnetic ordering; in addition, it increases the Curie temperature of the Cu–9Al–10Mn alloy.     

Conductivity of Al2(WO4)3–WO3 and Al2(WO4)3–Al2O3 Composites

Russian Journal of Electrochemistry - Composites of (1 – x)Al2(WO4)3–xWO3 and (1 – x)Al2(WO4)3–xAl2O3 are synthesized and their conductivity is studied as dependent on the...     

CO<Subscript>2</Subscript> capture by Mg–Al and Zn–Al hydrotalcite-like compounds

Hydrotalcite-like compounds (HTC) are distinguished by their properties for CO₂ capture, like high surface area, basic sites, thermal stability and good adsorption/desorption efficiency. Mg–Al e Zn–Al HTCs with Al³⁺ molar ratios x = 0.20, 0.28 and 0.33 were synthesized by coprecipitation, and subsequently calcined at 400 °C. For both HTCs, X-ray diffraction patterns have attested the formation of mixed oxides through calcination. The amount of basic sites, measured by temperature-programmed desorption of CO₂, decreases as x increases. The CO₂ adsorption was performed in a thermogravimetric balance using an adsorption temperature of 50 °C. Mg–Al and Zn–Al samples with x = 0.33 molar composition presented the highest CO₂ adsorption, 0.91 and 0.21 mmol g^?1, respectively. The Langmuir isotherm fitted well to the experimental data. It was also found that increasing the number of adsorption/desorption cycles the CO₂ adsorption decreases, which is associated with the irreversible chemisorption.     

Reactions of β-diketiminatoaluminum hydrides with tert-butyl hydrogenperoxide – Facile formation of dialuminoxanes containing Al–O–Al groups

Treatment of diphenyl-β-diketiminatoaluminum dihydride, LAlH₂ [1, L = {H₅C₆–NC(Me)}₂CH] with neopentyl- or trimethylsilylmethyllithium afforded the corresponding alkylderivatives LAlH(R) [R = CH₂–SiMe₃ (2), CH₂–CMe₃ (3)] by the precipitation of lithium hydride. Deprotonation of a methyl group instead of salt elimination occurred by the similar reaction of the more basic alkyllithium compound LiC(SiMe₃)₃. The reactions of the hydrides 1–3 with tert-butyl hydrogenperoxide did not yield the expected peroxo derivatives, instead the dialuminoxanes LAl(R)–O–Al(R)L [R = OCMe₃ (5), CH₂SiMe₃ (6), CH₂CMe₃ (7)] were isolated in high yields. Their Al–O–Al bridges deviated from linearity and had Al–O–Al bond angles of about 155° on average.     

Computer-aided cooling curve thermal analysis of near eutectic Al–Si–Cu–Fe alloy

The effects of bismuth (Bi), antimony (Sb) and strontium (Sr) additions on the characteristic parameters of the evolution of aluminium dendrites in a near eutectic Al–11.3Si–2Cu–0.4Fe alloy during solidification at different cooling rates (0.6–2 °C) were investigated by computer-aided cooling curve thermal analysis (CA-CCTA). Nucleation temperature ( $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ ) is defined with a new approach based on second derivative cooling curve. The results showed that $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ increased with increasing cooling rate but both the growth temperature ( $ T_{\text{G}}^{{\alpha {\text{ - Al}}}} $ ) and the coherency temperature (T _DCP) decreased. Increase in the temperature difference for dendrite coherency ( $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} - T_{\text{DCP}} $ ) with increasing cooling rate indicate a wider range of temperature before the dendrite can impinge on each other and higher fraction solid ( $ f_{\text{S}}^{\text{DCP}} $ ). Additions of Bi, Sb and Sr to the base alloy produced only a minor effect on $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ . Additions of Bi and Sb resulted in an increase in fraction solid and an increase of 30 % in the value of $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} \, - \,T_{\text{G}}^{{\alpha {\text{ - Al}}}} $ to almost 13 °C.     

Electrochemical and structural characterization of sputter-deposited Mg–Nb and Mg–Nb–Al–Zn alloy films

Nanocrystalline Mg–Nb and Mg–Nb–Al–Zn alloy films were deposited by dc magnetron sputtering on glass and quartz substrates in a wide range of niobium concentrations from 6 to 80 at.%. Structural, electrochemical and corrosion properties of the films were studied by X-ray diffraction, dc voltammetry, electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance. Development of body-centred cubic Nb structure in the Mg–Nb alloy matrix yielded the effects of lattice contraction, grain refining and electrochemical passivity. The measurements showed high corrosion resistance of the films in alkaline solutions when niobium content was one third or more. An increased corrosion resistance was achieved by introducing minor amounts of Al (ca. 2 at.%). In particular, such Al effect was pronounced at lower Nb concentrations (20 to 30 at.%). Semiconductor properties of spontaneously formed oxide on Mg–Nb alloy were studied by Mott–Schottky plots, which indicated highly doped n-type oxide structures on Mg–Nb surface. The paper fills some gap in understanding of niobium–magnesium systems, which show potential for applications in hydrogen storage, switchable mirrors and corrosion protection.     

Synthesis of Mg–Al–Fe–NO3 layered double hydroxides via a mechano-hydrothermal route

Mg–Al–Fe–NO₃ layered double hydroxides (LDHs) with a constant Mg²⁺/(Al³⁺ + Fe³⁺) molar ratio but varying Al³⁺/Fe³⁺ molar ratios were successfully synthesized by a mechano-hydrothermal (MHT) method from Mg(OH)₂, Al(OH)₃ and Fe(NO₃)₃·9H₂O or Mg(NO₃)₂·6H₂O as starting materials. The resulting LDHs (MHT-LDHs) were characterized by XRD, TEM, SEM, FT-IR, and zeta potential, size distribution and specific surface area analyses. It was found that pre-milling played a key role in the LDH formation during subsequent hydrothermal treatment. The MHT route is advantageous in terms of low reaction temperature compared with the conventional hydrothermal method, and the target products are of high crystallinity and good dispersion compared with the conventional mechanochemical (MC) method. The MHT-LDHs had higher specific surface area and zeta potential, and lower hydrodynamic diameter than LDHs obtained by MC method (MC-LDHs). Furthermore, the removal of Cr(VI) from aqueous solutions using the LDHs was examined, showing that the MHT-LDHs are of higher removal efficiency than MC-LDHs for the heavy metal pollutant.     

Electrochemical performance of Mg–9Al–1Zn alloy in aqueous medium

A systematic study on the corrosion and passivation behavior of AZ91D alloy in relation to the influence of concentration, temperature, pH, and immersion time was made in aqueous sulfate solution using electrochemical techniques including open-circuit potential, potentiodynamic polarization and impedance spectroscopy. It was found that the corrosion and pitting potentials (E _corr and E _pit) of the alloy drift to more active values with increasing either concentration (0.01–1.0 M) or temperature (278–338 K) of the test solution, suggesting that sulfate solution enhances the alloy dissolution, particularly at higher temperatures. On the other hand, values of the total film resistance (R _T) indicate that neutral solution (pH 7.0) supports the formation of a better protective layer on AZ91D surface than alkaline (pH 12.5) or acidic (pH 1.0) medium. The growth of a protective film on the alloy surface at short immersion times (up to ∼50 h) is evinced by a rapid positive evolution of E _corr and fast decrease in the corrosion rate (i _corr). However, for a long-term exposure (up to 500 h) E _corr drifts negatively and i _corr increases due to breakdown of the protective film, which causes a decrease in the alloy stability. Fitting the impedance data to equivalent circuit models suitable to each behavior assisted to explore the mechanism for the attack of the sample surface at various testing times. The results obtained from the three studied electrochemical techniques are in good agreement.     

Study on the microstructure and liquid–solid correlation of Al–Mg alloys

Based on the available structural models and theories of electrical resistivity (ER) of liquid alloys, the structure and the liquid–solid correlation of Al _(100-x) Mg_x (x = 0, 10, 20, 30, 40, 50) alloys have been qualitatively studied by measuring the ER during the heating/cooling process using the direct-current (DC) four-probe method, as well as by characterizing the solidification morphology and testing the hardness. The result shows that the ER of Al–Mg alloys increases with the increasing temperature and the Mg content; thermal state and history have an effect on the solidification structure and properties: the ER of Al–Mg alloys exhibits a lag phenomenon of structure change during the heating/cooling process. A higher heating/cooling rate contributes to the more obvious relaxation effect of ER and the more uniform structure. Furthermore, higher pouring temperature (PT) leads the melts and solidification structure to be more homogeneous, which increases the hardness.