Structure and phase composition of alloys of the Al-Ce-Cu system in the region of the Al-Al<Subscript>8</Subscript>CeCu<Subscript>4</Subscript> quasi-binary join

Phase diagram of the Al-Cu-Ce system is investigated in the region of the quasi-binary join Al-Al₈CeCu₄. The parameter of the eutectic reaction L → (Al) + CeCu₄Al₈ are found: T = 610°C; composition 14% Cu and 7% Ce. This eutectic has a dispersed structure, and the ternary compounds, which is involved in the eutectic, is capable to fragmentation and spheroidism in the course of heating starting from 540°C. It is shown that the region of optimal compositions of alloys based on the eutectic (Al) + CeCu₄Al₈ lies in narrow limits. This is caused by the fact that an abrupt decrease of the solidus and, as a consequence, significant broadening of the crystallization range occurs at a relatively small deviation from the ratio Cu: Ce = 2.     

Dissolution and melting of secondary Al2Cu phase particles in an AlCu alloy

When up-quenching an Al-4.2 wt pct Cu alloy which has been equilibrated at 450 °C to a temperature at or above the eutectic temperature of 547 °C, liquid drops are found to form. Inside the matrix grains they have a globular shape, while they have a lenticular shape with a low dihedral angle when formed on grain boundaries. It is demonstrated metallographically that drops are formed by the melting of the Al₂Cu phase particles together with the surroundingα matrix to form a liquid of chemical composition around the eutectic composition. On prolonged annealing, the drops are dissolved in theα matrix. The kinetics of this dissolution reaction of the drops, as well as the dissolution of Al₂Cu phase particles at a temperature below 547 °C, is studied in some detail and compared with a simple mathematical model. Also, the thermodynamics of the melting and dissolution reactions are discussed by means of a free-energy diagram.     

Fluidized bed heat treatment of cast Al-Si-Cu-Mg alloys

The effects of fluidized bed heat treatment on the microstructural and mechanical properties of Al-Si-Cu-Mg cast alloys, namely, 354 and 319, were studied. The heating rate in fluidized beds (FBs) is greatervis-à-vis conventional electrical resistance furnaces (CFs). The high heating rate in FBs increases the kinetics of metallurgical phenomena such as Si fragmentation and spherodization during solution heat treatment, as well as the precipitation rate of phases such as Al₅Cu₂Mg₈Si₆ and Al₂Cu during aging. It is observed that the dissolution rate of phases such as Mg₂Si and Al₅Cu₂Mg₈Si₆ takes place very rapidly. The solution heat treatment of 319 alloy using FB results in complete dissolution of Mg₂Si and Al₅Cu₂Mg₈Si₆ particles within 45 minutes. However, for phases such as Al₂Cu and Ferich intermetallics, the dissolution rate is relatively slow. Even on prolonged solution heat treatment for 6 hours, these phases do not dissolve completely. It is observed that incomplete dissolution of the Al₂Cu phase does not significantly affect tensile properties of T4-treated alloys. The optimum solution heat-treatment time in FB for both 354 and 319 alloys is 45 minutes at 527 °C and 493 °C, respectively. Thermal analysis shows an exothermic peak owing to recrystallization and coarsening of eutectic grains during solution heat treatment. The high heating rate in FB causes this transformation to take place at a lower temperature than in CF. It is observed that the nucleation rate of Al₅Cu₂Mg₈Si₆ during aging in FB is greater than using CF. Thermal analysis of samples during the ramp-up stage while aging using FB did not show any phase transformation, while those using CF show two endothermic transformations, which are most likely due to the dissolution of GP zones or the co-cluster of solutes. Aging at 200 °C results in a greater number density of precipitates than those at 240 °C. The tensile strength of samples aged at 200 °C is greater than those aged at 240 °C, because the amount of precipitates formed at 200 °C is greater than that at 240 °C. The total heat-treatment time for T6 temper is less than 2 hours in FBs, which is a significant reduction in heat-treatment time, as well as energy consumption.     

Heterogeneous nucleation of Al2Cu in AlCu eutectic liquid droplets embedded in an al matrix

The heterogeneous nucleation of Al₂Cu in AlAl₂ Cu eutectic liquids droplets embedded in an Al matrix has been studied by a combination of optical microscopy, transmission electron microscopy and differential scanning calorimetry. Nucleation of Al₂Cu is stimulated catalytically by the surrounding matrix at a temperature approx. 25°C below the eutectic temperature. With increasing cooling rate, the solidification onset, peak and end temperatures decrease and the peak height and width of the solidification exotherm increase. the contact angle at the AlAl₂ Cu liquid triple point is calculated to be 24.6° from the variation of exothermic peak width with cooling rate, but the corresponding calculated value of the number of potential catalytic nucleation sites is physically unrealistic.     

Microstructures of Al–Cu–Ag Ternary Eutectics Under Near-Isothermal Conditions

The three-phase eutectic microstructures in Al–Cu–Ag ternary alloys are complex and only directional solidification (DS) structures have been systematically studied in the literature. In order to better understand the large variation of eutectic structures in this system, three off-eutectic alloys in the vicinity of the nonvariant eutectic composition were solidified in a differential scanning calorimeter (DSC). The DSC was operated between 450 and 550 °C and at a heating and cooling rate of 1 °C/min to produce near-isothermal conditions. The intermetallic phase ζ-Ag₂Al is found to behave like pure metallic phase and forms primary dendrites. The ζ-Ag₂Al phase has a regular morphology in eutectics, while the θ-Al₂Cu exhibits big anisotropy of intermetallic nature and shows elongated morphology in the unconstraint grown eutectics. Three basic eutectic structures are categorized based on the relative phase arrangement: (1) semi-regular eutectic with elongated θ-Al₂Cu; (2) regular eutectic with rod-like ζ-Ag₂Al embedded in θ-Al₂Cu and (3) irregular eutectic with θ-Al₂Cu in ζ-Ag₂Al. They have nearly the same phase fraction and composition but distinct phase size distribution. The DSC eutectic structures are compared with reported DS eutectic structures.     

Influence of Nb and Cu Elements on the Intermetallic Particles Morphology in Ti/Al Multilayer Composite Processed Through Hot Pressing and Rolling

Ti–Al–Nb composites were produced by solid state diffusion bonding through hot pressing and rolling followed by annealing at 700 °C for 0.5, 1, 1.5 and 2 h. The morphologies of TiAl₃ intermetallics were investigated by Scanning Electron Microscopy combined with Energy-dispersive X-ray spectroscopy. Titanium tri-aluminide (TiAl₃) particles with blocky morphology were dispersed into Aluminum matrix. In the presence of niobium and copper, TiAl₃ particles were produced in different sizes and morphologies. The presence of Nb in the composite led to the formation of irregular angular morphology, while the copper resulted in cubic morphology of the intermetallic particles. The EDS results indicated that TiAl₃, (Ti, Nb)Al₃ and (Ti, Nb, Cu)Al₃ intermetallic compounds appeared near Ti zone, Nb Zone and in the presence of Cu, respectively.     

Effect of scandium on the phase composition and hardening of casting aluminum alloys of the Al–Ca–Si system

The phase composition of the Al–Ca–Si–Sc system is investigated in aluminum corner uisng computational (Thermo-Calc) and experimental (optical microscopy, scanning electron microscopy, and electron probe microanalysis) methods. The influence of annealing on the structure and hardness of alloys containing 0.3 wt % Sc is investigated in the region up to 550°C. It is shown that the maximum in the hardening curve caused by the isolation of nanoparticles of the Al₃Sc (L1₂) is attained after annealing at temperatures of 300–350°C in alloys belonging to the phase region (Al) + Al₄Ca + Al₂Si₂Ca ((Al) is the aluminum-based solid solution). Scandium completely enters the (Al) composition in alloys of this region, while the silicon concentration is minimal in it. On the other hand, hardening is almost absent in alloys from the (Al) + (Si) + Al₂Si₂Ca phase region. The possibility in principle to form the casting alloys based on the (Al) + Al₄Ca + Al₂Si₂Ca eutectic hardened without quenching is substantiated.     

Influence of a Silicon Additive on Resistivity and Hardness of the Al–1% Fe–0.3% Zr Alloy

Isothermal sections of the diagram of the Al–Fe–Si–Zr alloy at temperatures of 450 and 600°C, as well as polythermal sections at concentrations of silicon up to 2 wt % and zirconium up to 1 wt %, are analyzed using computational methods with the help of Thermo-Calc software. It is shown that the favorable phase composition consisting of the aluminum solid solution (Al), the Al₈Fe₂Si phase, and Zr (which completely enters the composition of the solid solution (Al) during the formation of the cast billet) can be attained in equilibrium conditions at silicon concentrations of 0.27–0.47 wt %. To implement the above-listed structural components in nonequilibrium conditions and ensure that Zr enters the (Al) composition, experimental ingots were fabricated at an elevated cooling rate (higher than 10 K/s). A metallographic analysis of the cast structure of experimental samples revealed the desired structure with contents of 0.25 wt % Si and 0.3 wt % Zr in the alloy. The microstructure of the Al–1% Fe–0.3% Zr–0.5% Si alloy also contains the eutectic (Al) + Al₈Fe₂Si; however, the Al₈Fe₂Si phase partially transforms into Al₃Fe. The structure of the alloy with 0.25 wt % Si in the annealing state at 600°C contains fragmented particles of the degenerate eutectic (Al) + Al₈Fe₂Si along the boundaries of dendritic cells. It is established that the Si: Fe = 1: 2 ratio in the alloy positively affects its mechanical properties, especially hardness, without substantially lowering the specific conductivity during annealing, which is explained by the formation of the particles of the Al₈Fe₂Si phase of the compact morphology in the structure. Moreover, silicon accelerates the decay of the solid solution by zirconium, which is evidenced by the experimental plots of the dependence of hardness and resistivity on the annealing step. The best complex of properties was shown by the Al–1% Fe–0.3% Zr–0.25% Si alloy in the annealing stage at 450°C with the help of the optimization function at specified values of hardness and resistivity.     

Phase equilibria of the ternary Al-Cu-Ni system and interfacial reactions of related systems at 800 °C

A series of Al-Cu-Ni alloys of various compositions were made and annealed at 800 °C. The equilibrium phases were studied by metallography, X-ray diffraction (XRD) analysis, and electron probe microanalysis. The isothermal section of the ternary Al-Cu-Ni system at 800 °C was then determined based on these experimental results and the available phase relationship knowledge of the three constituent binary systems. No ternary compound was found. All three phases, AlNi₃, AlNi, and Al₃Ni₂, have very high ternary solubility, especially the AlNi phase, which almost reaches the binary Al-Cu side. However, no continuous solid solution was formed between the AlNi phase and any of the binary Al-Cu phases. Interfacial reactions of Al/Ni, Al/Cu, Al-Cu/Ni, and Al-Ni/Cu at 800 °C were investigated by using reaction couple techniques. The results showed that Al₃Ni and Al₃Ni₂ phases were formed in the Al/Ni couples; β-AlCu₄, γ ₁-Al₄Cu₉, and ɛ ₂-Al₂Cu₃ phases were formed in the Al/Cu couples. As for the results in the Al-2 at. pct Ni/Cu, Al-5 at. pct Ni/Cu, and Al-2 at. pct Cu/Ni, Al-4.5 at. pct Cu/Ni, and Al-6 at. pct Cu/Ni were similar to those in the binary Al/Cu and Al/Ni couples, respectively. A different reaction path was found in the Al-7.5 at. pct Cu/Ni couples, and an AlNi solid solution layer was formed instead of the Al₃Ni and Al₃Ni₂ phases.     

Infrared brazing Cu and Ti using a 95Ag-5Al braze alloy

Dynamic wetting angle measurements, microstructural evolution, reaction kinetics, and shear strength of infrared brazing Cu and Ti using a 95Ag-5Al braze alloy are evaluated. The specimen infrared brazed at 900 °C consists mainly of Cu₂Ti and Cu₄Ti. Both CuTi and Cu₄Ti₃ are observed at the interface between the braze and Ti substrate. Microstructures of Ti/95Ag-5Al/Cu joints infrared brazed at 830 °C and 850 °C are very different from that of the joint infrared brazed at 900 °C, because the dissolution of both substrates significantly decreased as the brazing temperature decreased. Specimens infrared brazed at 830 °C and 850 °C are primarily comprised of Ag-Cu eutectic and the Cu-rich phase. Two interfacial reaction layers, including Ti₂Cu and AlCu₂Ti, are found in the experiment. The shear strengths of infrared brazed specimens at 830 °C and 850 °C are between 160 and 198.5 MPa, and are fractured along the interfacial reaction layers, AlCu₂Ti and Ti₂Cu, between the braze alloy and Ti substrate. The use of the infrared brazing provides an effective way to inhibit the growth of intermetallics at the interface between the braze alloy and substrate.     

Sintering and aging behaviours of Al4CuXMg PM alloy

Sintering and aging behaviours of Al–Cu–Mg powder metallurgy (PM) alloy produced from elemental powders were examined. After evaluating results from thermal analysis, tests were carried out on Al–4Cu alloys with magnesium contents of 0.5, 1 and 2?wt-% and it was found that additions of 1?wt-% Mg was most effective for enhancing the transverse rupture strength (TRS) of the Al–Cu PM alloys for both as sintered and after a heat-treatment conditions. Grain size reduction in the range of 14–45% was achieved by adding magnesium into Al–Cu system. Analyses showed that produced alloys were composed of Al, Al₂Cu, Al₂CuMg and Al₇Cu₂Fe phases. Differential scanning calorimeter and dilatometer analyses revealed that alloys show swelling behaviour after the eutectic melting reaction at 548°C and swelling rates increasing as a function of magnesium content. Both high hardness value (120 HB) and TRS (650?MPa) were achieved via aging of Al4Cu1Mg alloy for 24 hours.     

<Emphasis Type="Italic">In-Situ</Emphasis> Synthesis of Cu/Cr-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocomposite by Mechanical Alloying and Heat Treatment

In this article, a novel method has been used to prepare a copper matrix nanocomposite containing Cu-10 wt pct Cr-10 wt pct Al₂O₃ by heat treatment of the mechanically activated Cu, Al, and Cr₂O₃ powder mixture. Structural evolutions were investigated using the X-ray diffraction (XRD) technique. The microstructure of samples was examined using scanning electron microscopy (SEM). It was found that during the milling process, Cu(Al) solid solution and Cu₉Al₄ phase were formed as the intermediate products, and therefore, Al activity was decreased. Hence, the reduction of Cr₂O₃ with Al was prevented during the ball milling stage. Further heat treatment carried out under argon atmosphere at 900 °C for 8 hours resulted in completion of Cr₂O₃ reduction by Al.     

A study on the microstructural evolution of Al-25 at. pct V-12.5 at. pct M (M = Cu,Ni, Mn) powders by planetary ball milling

The alloying behavior of Al-25 at. pct V-12.5 at. pct M (M = Cu, Ni, Mn) by planetary ball milling of elemental powders hours as been investigated in this study. In Al₃V binary system, an amorphous phase was produced after 6 hours and the amorphous phase was mechanically crystallized after 20 hours. The large difference in the diffusivities between Al and V atoms in Al matrix results in the formation of the amorphous phase when the homogeneous distribution of all the elements in a powder was achieved at 6 hours. According to thermal analyses, the amorphous phase in the binary Al₃V was crystallized at 350 °C. The addition of ternary elements (Cu, Ni, Mn) increased the activation energy for the crystallization to D0₂₂ phase by interfering with the diffusion process. Therefore, ternary element addition improved the thermal stability of the amorphous structures. The amorphous phase in the 12.5 at. pct Ni added Al₃V was crystallized to D0₂₂ phase at 540 °C. The mechanical crystallization of the amorphous phase in the ternary element-added Al-V system either occurred later or was not observed during ball milling up to 100 hours. It is thought that the amorphous intermetallic compacts could be produced more easily in ternary element-added alloys by using an advanced consolidation method.     

Precipitate stability in AlCuMgAg alloys aged at high temperatures

A study has been made of the thermal stability of the Ω phase in AlCuMgAg alloys aged at high temperatures (200 to 350°C). This phase, which precipitates as thin plates on the {111}_α planes, has been shown to be replaced by the equilibrium precipitate θ (Al₂Cu) after prolonged ageing (e.g. 2400 h at 250°C). Measurements have been made of the thickening behaviour of the Ω plates and the various orientations and morphologies of the θ phase have been characterised. Whilst there is some evidence for the direct allotropic transformation of Ω to θ, it is concluded that a gradual dissolution/re-precipitation mechanism dominates the changes to microstructure at these high temperatures. Although magnesium and silver are known to segregate to the Ω phase, they were not detected in association with θ. Rather they were found to partition to sites of the S phase (Al₂CuMg) which forms as a minor precipitate under these ageing conditions.     

Synthesis of Al -TiC in-situ composites: Effect of processing temperature and Ti:C ratio

Al-TiC insitu composites are gaining increasing importance because of good wettability of TiC with Al melt and its favourable properties. However, incomplete reaction between the released Ti and C in Al melt leads to formation of undesirable phases like Al₃Ti which is detrimental to the properties. In this investigation, Al-TiC composites are processed at different temperatures from 700 °C to 1200 °C and with different Ti:C ratios to asses the effect of these two parameters on the formation of TiC particles. Microstructural features and X-ray diffraction results show that at temperatures below 1000 °C blocky type Al₃Ti forms. As the temperature is increased the blocky nature of Al₃Ti changes to needle like indicating release of Ti to a greater extent and as a result more and more TiC particles form. At 1200 °C there is no evidence of Al₃Ti formation after a reaction time of 30 minutes. Increasing the carbon content (Ti:C ratio) to two fold of the stoichimetric amount does not show any significant effect. Though a four fold increase in carbon content showed some promise, however, some amount of free carbon was found to remain.     

Evolution of microstructure and tensile strength of rapidly solidified Al-4.7 pct Zn-2.5 pct Mg-0.25 pct Zr-X wt pct Mn alloys

Analytical transmission electron microscopy and thermal analysis of as-extruded Al-4.7 pct Zn-2.5 pct Mg-0.2 pct Zr-X wt pct Mn alloys, with Mn contents ranging from 0.5 to 2.5 wt pct, were carried out to elucidate the microstructural change and accompanying mechanical properties during subsequent heat treatments. The as-extruded alloy was fabricated from rapidly solidified powder and consisted of a fine, metastable manganese dispersoid and the ternary eutectic T phase (Al₂Mg₃Zn₃). Solution heat treatment resulted in the formation of the stable Al₆Mn phase and complete dissolution of the T phase. Formation of stable Al₆Mn was made by two routes: by phase transition from metastable Mn dispersoids which already existed, and from the supersaturated solid solution by homogeneous nucleation. The density of the Al₆Mn phase increased with the addition of manganese, while the shape and average size remained unchanged. A significant increase in the hardness was observed to coincide with the formation of the Al₆Mn phase. Similarly, the tensile strength increased further after the aging treatment, and the increment was constant over the content of Mn in the alloy, which was explained by the contribution from the same amount of precipitates, MgZn₂. Results of thermal analysis indicated that the dissolution of the T phase started near 180 °C and that formation of Al₆Mn occurred at about 400 °C, suggesting that further enhancement of strength is possible with the modification of the heat-treatment schedule.     

Investigation into the Possibility of Fabricating Boraluminum Rolling of Increased Strength without Homogenization and Quenching

Aluminum alloys of the Al–Cu–Mn (Zr) system possess high strength and manufacturability without heat treatment (HT). In order to investigate the possibility of fabricating an aluminum boron-containing alloy in the form of sheet rolling with increased strength without the HT, Al–2% Cu–1.5% Mn–2% B and Al–2% Cu–1.5% Mn–0.4% Zr–2% B alloys are prepared. To exclude the deposition of refractory boride particles, smelting is performed in a RELTEK induction furnace providing intense melt stirring. The smelting temperature is 950–1000°C. Pouring is performed into 40 × 120 × 200 mm graphite molds. It is established using computational methods (Thermo-Calc) that manganese forms complex borides with aluminum and zirconium at the smelting temperature and a sufficient amount of manganese remains in liquid, while zirconium is almost absent in it. The formation of AlB₂Mn₂ complex boride is proved experimentally (scanning electron microscopy and micro X-ray spectral analysis), but the amount of manganese remaining in the solid solution is sufficient to form particles of the Al₂₀Cu₂Mn₃ phase in an amount reaching 7 wt %. Boron in the zirconium-containing alloy stimulates the isolation of primary crystals Al₃Zr, in connection with which an insufficient amount of zirconium remains in the aluminum solid solution for strengthening. The possibility of fabricating thin-sheet rolling smaller than 0.3 mm in thickness with uniformly distributed agglomerations of the boride phase with a particle size smaller than 10 µm is shown. A high level of strength (up to 543 MPa) is attained with no use of quenching or aging due to the isolation of dispersoids of the Al₂₀Cu₂Mn₃ phase during hot deformation (t = 450°C).     

Structural study of electrodeposited aluminum-manganese alloys

Aluminum-manganese alloys with compositions ranging between 0 and 27 wt pct Mn were electrodeposited at 150°C onto copper substrates from a chloroaluminate molten salt electrolyte with a controlled addition of MnCl₂. The specimens were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The addition of small amounts of Mn results in the formation of a supersaturated fcc solid solution of Mn in Al. At the higher Mn content, an amorphous phase is established. The highly faceted crystalline surface of pure Al and Al−Mn solid solution becomes smooth and nearly specular when the amorphous phase is present. The amorphous phase appears in the form of rounded grains and has a lower limit of Mn concentration close to the Al₆Mn composition. There is a concentration discontinuity between the above limit and the higher Mn concentration limit of the fcc phase (about 9 wt pct). Appearance of the amorphous phase in the alloy results in a decrease in the Mn concentration in solid solution to about 2 wt pct. Crystallization of the amorphous phase starts at the fcc-amorphous phase interface at 230°C. As a result of treatment at 230 °C to 340 °C, the amorphous phase completely transforms into Al₆Mn, while the fcc phase is unaffected. Prior to crystallization, the amorphous phase shows a modification that could be interpreted as the formation of a fine-grained icosahedral phase. The formation and distribution of phases by electrodeposition and rapid solidification are discussed.     

Formation of Liquid and Intermetallics in Al-to-Mg Friction Stir Welding

In dissimilar-metal friction stir welding (FSW), intermetallic compounds can form in the stir zone and significantly reduce the joint strength. The formation of intermetallic compounds in Al-to-Mg FSW was investigated in lap and butt FSW of the widely used 6061 Al and AZ31B Mg and discussed using the binary Al-Mg phase diagram as an approximation. Temperature measurements during lap FSW indicated a 703 K (430 °C) peak temperature, slightly below the eutectic reaction (Mg) + Al₁₂Mg₁₇ → L at 710 K (437 °C), because the thermocouples were pushed downward during welding. The intermetallic compounds in the stir zone were revealed by color etching and identified by X-ray diffraction (XRD), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM) as Al₃Mg₂ and Al₁₂Mg₁₇. Additional FSW was conducted near the edge of the upper sheet, and the liquid droplets squeezed out during welding solidified along the edge. Optical microscopy of the solidified droplets and EPMA revealed dendrites of Al₃Mg₂ and Al₁₂Mg₁₇ and interdendritic eutectics, thus indicating eutectic reactions (Mg) + Al₁₂Mg₁₇ → L (710 K (437 °C)) and (Al) + Al₃Mg₂ → L (723 K (450 °C)). Differential scanning calorimetry (DSC) confirmed that the solidified droplets melted at 709 K (436 °C) and 722 K (449 °C), nearly identical to the eutectic temperatures. Formation of intermetallic compounds on the order of 1 mm in size suggests they form upon solidification of the liquated material instead of solid-state diffusion.     

Effect of Ultrasonic Vibration on Direct Reaction Between Solid Ti Powders and Liquid Al

In-situ blocky Al₃Ti particles can be synthesized by direct reaction between solid Ti powders and liquid Al in terms of reaction-peeling model. In this research, the effect of high-intensity ultrasonic vibration on the reaction was investigated by means of immersing the ultrasonic radiator in the Al melt at 1003 K (730 °C) during the fabricating process. The results show that the thickness of Al₃Ti reaction layers can be decreased to range from 2 to 3 μm, and the sizes of most of Al₃Ti particles can be reduced in the ultrasonic fields as well, with the average size ranging from 2 to 3 μm. The two changes are both attributed to the effects of external forces produced in the ultrasonic fields. Thereby, small blocky Al₃Ti particles can be peeled off from the reaction layer more quickly, making reaction layers to become thinner and the particles smaller.