Extrusion of spray-formed Al–25Si–X composites and their evaluation

A comprehensive methodology to fabricate an Al–25Si–X composite via spray-forming and extrusion was investigated to judge the potential of this alloy for applications requiring high strength as well as high wear resistance and/or high elastic modulus. Billets were spray-formed with a low gas/metal ratio of about 0.8 m³/kg to reduce the consumption of nitrogen gas. The billets, having considerable porosity, were then extruded into sub-scale bars using various extrusion parameters, such as extrusion ratio, die temperature, and die configuration to optimize the extrusion conditions and eliminate the pores in the preform. Based on results obtained from the preliminary sub-scale extrusion tests, the spray-formed billets were then hot extruded into a tubular shape with outer and inner diameters of 97 mm × 77 mm, respectively, at an extrusion temperature of 500 °C. Various material properties of the extruded tubes were measured and compared with other candidate materials for these applications.     

Development of ultrafine grained high strength Al–Cu alloy by cryorolling

In the present paper, the microstructure and mechanical properties of a precipitation hardening Al–Cu (2219) alloy subjected to cryorolling, low temperature annealing and ageing treatments are reported. Under optimal processing conditions, ultrafine grained microstructure with improved tensile strength (540 MPa) and good ductility (11% tensile elongation) was obtained.     

Influence of Ti addition on the microstructure and hardness properties of near-eutectic Al–Si alloys

In this study, the influence of Ti addition on the microstructure and hardness of near-eutectic Al–Si has been investigated. Near-eutectic Al–Si alloys (13.1 wt.% Si) with 0.1, 1, 2, 3, 5, and 10% Ti have been utilized for this purpose. The melting operation was carried out in an electrical furnace, where the charge materials were placed in a graphite crucible. After melting, alloys have been cast in the metal mold at 1100 °C and solidified.     

Improvement of product strength and formability in stamping of Al–Mg–Si alloy sheets having bake hardenability by resistance heat and artificial aging treatments

Resistance heat and artificial aging treatments were introduced into a stamping operation to improve the product strength and formability of Al–Mg–Si alloy sheets having bake hardenability used for automobile body panels. In this treatment, the sheets undergo re-solution by resistance heat treatment, composed of resistance heating and water quenching just before the stamping. Stamped sheets are artificially aged just after the stamping to increase product strength. In the experiment, Al–0.60% Si–0.74% Mg alloy sheets were chosen as an example of Al–Mg–Si alloy sheets having bake hardenability. The re-solution solution treatment of the sheets was sufficiently accomplished by rapid resistance heat treatment, and formability of the sheets was improved. Hardness of the formed products was increased by artificial aging. It was found that the present process is effective in improving the product strength and formability of Al–Mg–Si alloy sheets having bake hardenability due to the compactness and rapidness.     

Effect of a high axial magnetic field on the microstructure in a directionally solidified Al–Al2Cu eutectic alloy

The effect of a high axial magnetic field (up to 12 T) on the microstructure in a directionally solidified Al–Al₂Cu eutectic alloy has been investigated experimentally. The results show that a high magnetic field decreases the eutectic spacing and degenerates the lamellar structure into a wavy one at a low growth speed. X-ray diffraction, selected-area electron diffraction and high-resolution electron microscopy analyses indicate that the field changes the preferred orientation. The Al₂Cu crystal is oriented with the 0 0 1-crystal direction along the solidification direction (i.e., the magnetic field direction). At a pulling velocity of 0.5 μm/s, the magnetic field (B  4T) is responsible for the segregation; which consists of Al striations on the longitudinal section and Al-rich zones on the transverse section. The effects of the field may be attributed to the orientation of the Al₂Cu and the Al crystals and the decrease of the diffusion coefficient caused by the magnetic field.     

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.     

Theory of the nonlinear internal friction associated with bulk diffusion of solute atoms around dislocations in Al–Mg alloys

In this paper the nonlinear (amplitude-dependent) internal friction (P₃ peak) in cold-worked Al–Mg alloys is theoretically studied by solving the bulk diffusion equations of the solute atoms (Mg atoms) under the action of dislocation drag. The results in the case of a constant external stress show that the bow-out distance of the dislocation has an exponential relation with time, which can be well described by an exponential creep function with a Gaussian distribution in τ. With the increasing strain amplitude, the relaxation strength Δ and relaxation time τ decrease, while the distribution parameter increases. Both activation energy H and pre-exponential factor τ₀ deduced from τ through Arrhenius relation are dependent on strain amplitude.     

Isothermal section of the Gd–Co–V ternary system at 773 K

The isothermal section of the phase diagram of the Gd–Co–V ternary system at 773 K was investigated by X-ray powder diffraction (XRD), metallographic analysis, electron probe microanalysis, and differential thermal analysis (DTA) techniques. The isothermal section consists of 14 single-phase regions, 26 two-phase regions and 13 three-phase regions. The solid solubilities of V in the compounds Co₁₇Gd₂, Co₃Gd, Co₂Gd, Co₇Gd₁₂ and CoGd₃ were about 10.0, 2.0, 6.0, 1.2 and 5.3 at.% V, respectively. It was found that there are some homogeneity range in the only ternary compound of GdCo_12−xV_x with x = 2.6–3.7 at 773 K. No solubility of Gd in compounds Co₃V, σCoV or CoV₃ was observed. There is no solubility of V in Co₇Gd₂ or Co₃Gd₄ observed at 773 K.     

Oxidation of a quaternary two-phase Cu–40Ni–17.5Cr–2.5Al alloy at 973–1073 K in 101 kPa O2

Oxidation of a quaternary two-phase Cu–40Ni–17.5Cr–2.5Al (at.%) alloy was investigated at 973–1073 K in 101 kPa O₂. The alloy is composed of two phases. One light phase with lower Cr content forms the matrix of the alloy, and the other medium gray phase richer in Cr is presented in the form of continuous islands. At 973 and 1073 K, the kinetic curves for the present alloy deviate evidently from the parabolic rate law. They show a large mass gain in initial stage, and then their oxidation rates decrease evidently with time until they become very small up to 24 h. Cross sectional morphologies show the present alloy is able to form continuous external scales of chromia over the alloy surface with a gradual decrease in the oxidation rate. However, the previous studies showed that a ternary two-phase Cu–40Ni–20Cr alloy is unable to form protective external scales of chromia over the alloy surface, but is able to form a thin and very irregularly continuous layer of chromia at the top of the mixed internal oxidation region. Therefore, substituting Cr in Cu–40Ni–20Cr alloy with 2.5 at.% Al is able to decrease the critical content required to form Cr oxide and help to form continuous external scales of chromia under lower Cr content in two-phase alloys.     

Phase transformation and morphology of the intermetallic compounds formed at the Sn–9Zn–3.5Ag/Cu interface in aging

The morphology and phase transformation of the intermetallic compounds (IMCs) formed at the Sn–9Zn–3.5Ag/Cu interface in a solid-state reaction have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The monoclinic η′-Cu₆Sn₅ transforms to the hexagonal η-Cu₆Sn₅ and the orthorhombic Cu₅Zn₈ transforms to the body-centered cubic (bcc) γ-Cu₅Zn₈ as aged at 180 °C. The scallop-shaped Cu₆Sn₅ layer is retained after aging at 180 °C for 1000 h. In the solid-state reaction, Ag is repelled from η′-Cu₆Sn₅ and reacts with Sn to form Ag₃Sn, and the Cu₅Zn₈ layer decomposes. Kirkendall voids are not observed at the Sn–9Zn–3.5Ag/Cu interface even after aging at 180 °C for 1000 h.     

Comparative analysis for the corrosion susceptibility of Cu,Al, Al–Cu and C‐steel in soil solution

Corrosion of different materials (Cu, Al, Al–Cu and C‐steel) in soil solution was evaluated at ambient temperature using various techniques. The weight loss of the studied materials varied exponentially with time. Kinetic data revealed that the corrosion of Cu and Al–Cu are diffusion controlled while Al and C‐steel show gradual change from diffusion control to charge transfer control. Nonferrous materials have better durability factors than C‐steel. Good consistency between the data obtained from EIS and PDP measurements was observed. SEM showed a biogenic corrosion layer with density that depends on the metal type. Correlation between corrosion rates and the estimated soil solution corrosivity was obtained.     

The third-element effect in the oxidation of Ni–xCr–7Al (x = 0, 5, 10, 15 at.%) alloys in 1 atm O2 at 900–1000 °C

The oxidation in 1 atm of pure oxygen of Ni–Cr–Al alloys with a constant aluminum content of 7 at.% and containing 5, 10 and 15 at.% Cr was studied at 900 and 1000 °C and compared to the behavior of the corresponding binary Ni–Al alloy (Ni–7Al). A dense external scale of NiO overlying a zone of internal oxide precipitates formed on Ni–7Al and Ni–5Cr–7Al at both temperatures. Conversely, an external Al₂O₃ layer formed on Ni–10Cr–7Al at both temperatures and on Ni–15Cr–7Al at 900 °C, while the scales grown initially on Ni–15Cr–7Al at 1000 °C were more complex, but eventually developed an innermost protective alumina layer. Thus, the addition of sufficient chromium levels to Ni–7Al produced a classical third-element effect, inducing the transition between internal and external oxidation of aluminum. This effect is interpreted on the basis of an extension to ternary alloys of a criterion first proposed by Wagner for the transition between internal and external oxidation of the most reactive component in binary alloys.     

The 260 °C phase equilibria of the Sn–Sb–Ag ternary system and interfacial reactions at the Sn–Sb/Ag joints

The isothermal section of the Sn–Sb–Ag ternary system at 260 °C has been determined in this study by experimental examination. Experimental results show no existence of ternary compounds in the Sn–Sb–Ag system. Two extensive regions of mutual solubility have been determined. The one located between the two binary isomorphous phases, Ag₃Sn and Ag₃Sb, is labeled as and the other one located between the two binary isomorphous phases, Ag₄Sn and Ag₄Sb, is labeled as ξ. The phase is a very stable phase and is in equilibrium with ξ, Sb, SbSn, Sb₂Sn₃, and liquid Sn phases. Each of the Sb and SbSn phases has a limited solubility of Ag. Only one stoichiometric compound, Sb₂Sn₃, exists. Besides phase equilibria determination, the interfacial reactions between the Sn–Sb alloys and the Ag substrate were investigated at 260 °C. It was found that the phase formations in the Sn–Sb/Ag couples are very similar to those in the Sn/Ag couples.     

A SEM and EDS insight into the BUL and BUE differences in the turning processes of AA2024 Al–Cu alloy

When a Built-Up Edge (BUE) and a Built-Up Layer (BUL) are formed on the rake face of a tool, the surface finishing of the workpiece, the tool geometry and other output parameters can be affected. Till a few years ago both effects were considered as two forms of the same phenomenon. More recently, some authors have established differences between BUL and BUE, those related to thickness. The mechanism of BUL and BUE formation is not taken into account by these authors. This work reports on the results of a study using the SEM and EDS of the microstructural features of BUL and BUE formed over TiN turning inserts in machining of an Al–Cu alloy. The results obtained in this study have allowed the establishment of a first hypothesis about the differences between the mechanisms of BUL and BUE formation.     

In situ impedance spectroscopy study of the electrochemical corrosion of Ti and Ti–6Al–4V in simulated body fluid at 25 °C and 37 °C

The corrosion resistance of Ti and Ti–6Al–4V was investigated through electrochemical impedance spectroscopy, EIS, potentiodynamic polarisation curves and UV–Vis spectrophotometry. The tests were done in Hank solution at 25 °C and 37 °C. The EIS measurements were done at the open circuit potential at specific immersion times. An increase of the resistance as a function of the immersion time was observed, for Ti (at 25 °C and 37 °C), and for Ti–6Al–4V (at 25 °C), which was interpreted as the formation and growth of a passive film on the metallic surfaces.     

Phase equilibria in the Fe–Al–Mo system – Part I: Stability of the Laves phase Fe2Mo and isothermal section at 800 °C

Phase equilibria in the Fe–Al–Mo system were experimentally determined at 800 °C. From metallography, X-ray diffraction and electron probe microanalysis on equilibrated alloys and diffusion couples a complete isothermal section has been established. It is shown that the Laves phase Fe₂Mo is a stable phase. The phase Al₄Mo, which only becomes stable above 942 °C in the binary system, is the only ternary compound found at 800 °C. For all binary phases the solid solubility ranges for the third component have been established. The D0₃/B2 and B2/A2 transition temperatures have been determined for a selected alloy by differential thermal analysis and transmission electron microscopy. The results confirm that the D0₃/B2 transition temperature substantially increases by the addition of Mo, while the B2/A2 transition temperature is about that for a binary alloy with the same Al content.     

Cycle stabilities of the La0.7Mg0.3Ni2.55−xCo0.45Mx (M = Fe, Mn, Al; x = 0, 0.1) electrode alloys prepared by casting and rapid quenching

In order to improve the cycle stability of La–Mg–Ni system (PuNi₃-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Fe, Mn and Al, and the electrode alloys La_0.7Mg_0.3Ni_2.55−xCo_0.45M_x (M = Fe, Mn, Al; x = 0, 0.1) were prepared by casting and rapid quenching. The effects of the substitution of Fe, Mn and Al for Ni and rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM indicate that element substitution has no influence on the phase compositions of the alloys, but it changes the phase abundances of the alloys. Particularly, the substitution of Al and Mn obviously raises the amount of the LaNi₂ phase. The substitution of Al and Fe leads to a significant refinement of the as-quenched alloy's grains. The substitution of Al strongly restrains the formation of an amorphous in the as-quenched alloy, but the substitution of Fe is quite helpful for the formation of an amorphous phase. The effects of the substitution of Fe, Mn and Al on the cycle stabilities of the as-cast and quenched alloys are different. The positive influence of the substitution elements on the cycle stabilities of the as-cast alloys is in proper order Al > Fe > Mn, and for as-quenched alloys, the order is Fe > Al > Mn. Rapid quenching engenders an inappreciable influence on the phase composition, but it markedly enhances the cycle stabilities of the alloys.