N. A. Belov

Structure, phase composition, and strengthening of cast Al–Ca–Mg–Sc alloys

The structure and phase composition of Al–Ca–Mg–Sc alloys containing 0.3 wt % Sc, up to 10 wt % Ca, and up to 10 wt % Mg have been investigated in the cast state and state after heat treatment. It has been shown that only binary phases Al4Ca, Al3Sc, and Al3Mg2 can be in equilibrium with the aluminum solid solution. It has been found that the maximum strengthening effect caused by the precipitation of Al3Sc nanoparticles for all investigated alloys is attained after annealing at 300–350°C.

Effect of 0.3% Sc on microstructure, phase composition and hardening of Al-Ca-Si eutectic alloys

Abstract The phase composition, microstructure and hardening of aluminum-based experimental alloys containing 0.3% Sc, 0–14% Si and 0–10% Ca (mass fraction) were studied. The experimental study (electron microscopy, thermal analysis and hardness measurements) was combined with Thermo-Calc software simulation for the optimization of the alloy composition. It was determined that the maximum hardening corresponded to the annealing at 300–350 °C, which was due to the precipitation of Al3Sc nanoparticles with their further coarsening. The alloys falling into the phase region (Al)+Al4Ca+Al2Si2Ca have demonstrated a significant hardening effect. The ternary eutectic (Al)+Al4Ca+Al2Si2Ca had a much finer microstructure as compared to the Al–Si eutectic, which suggests a possibility of reaching higher mechanical properties as compared to commercial alloys of the A356 type. Unlike commercial alloys of the A356 type, the model alloy does not require quenching, as hardening particles are formed in the course of annealing of castings.

Eutectic alloys based on the Al–Zn–Mg–Ca system: microstructure, phase composition and hardening

The experimental study of aluminium alloys based on the Al–Ca–Zn–Mg system (3.5% Mg and 2.5% Mg, 0–10% Ca, 0–14% Zn (wt-%)) was combined with Thermo-Calc simulations for the optimisation of the alloy composition. Zinc is distributed between aluminium solid solution and phase (Al,Zn)4Ca. Magnesium was not observed in the intermetallic phase. The eutectic (Al,Zn)4Ca had fine structure and particles of (Al,Zn)4Ca were capable of spheroidisation during the heat treatment at 520°С. The maximum level of hardness observed in calcium-containing alloys was higher than 200 HB, suggesting good strength properties. With an example of the Al–Zn(9%)–Mg(3.5%)–Ca(3%) alloy, the possibility of manufacturing thin rolled sheets based on the (Al)–Ca eutectic was demonstrated. This article is part of a Themed Issue on Aluminium-based materials: processing, microstructure, properties, and recycling.

Economically doped high-strength deformed nikalines as aluminum alloys of a new generation

The phase composition of the Al-Zn-Mg-Cu-Cr-Mn-Zr-Fe-Si-Ni system is performed as applied to high-strength aluminum alloys of the V96 type. It is revealed that, in the absence of copper, manganese, and chromium, the amount of possible phases is reduced by more than a factor of 3. The data of a calculation with the use of Thermo-Calc indicate that the Al-Zn-Mg-Ni-Fe system is the most promising for the development of a new group of high-strength deformed alloys such as economically doped nikalines based on (Al) + Al9FeNi eutectics. Using the example of nikaline ATs7NZh, which contains more than 10% (Zn + Mg), it is shown that high mechanical properties are achieved in the rods: σv > 670 MPa, σ0.2 > 640 MPa, and δ > 6%.

Influence of iron and silicon on the phase composition and structure of heat-resistant casting nikalines strengthened by nanoparticles

The phase composition of the Al-Ni-Mn-Fe-Si-Zr system is analyzed as applied to heat-resistant nikalines (aluminum alloys of a new generation based on Ni-containing eutectic), which are strengthened by the Al3Zr (L12) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat-resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).

Effect of Calcium on Structure, Phase Composition and Hardening of Al-Zn-Mg Alloys Containing up to 12wt.%Zn

The influence of calcium on structure and phase composition of the aluminum alloys, containing additions of zinc up to 12 wt.% and magnesium (3.5 wt.%) was studied. The increase of Zn content leads to formation of Al4Ca primary crystals at lower concentrations of calcium. Zinc is distributed between aluminum solid solution and intermetalic phases (Ca-containing and T- Al2Mg2Zn3) in the alloys of the Al-Zn-Mg-Ca system. The eutectic (Al)+Al4Ca has fine structure and particles of Al4Ca are capable to spheroidization during heat treatment at 500 °С. The maximal level of hardness observed on calcium containing alloys was higher than 200 HB, what gives a reason to expect good strength properties. Due to summarized results it is seen that the Al-Zn-Mg-Ca system is promising for development of new eutectic type high-strength aluminum alloys.

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.

Investigation into the Fabrication Possibility of the Boron–Aluminum Sheet Rolling of Increased Strength without Using Homogenization and Quenching

Al–Cu–Mn (Zr) aluminum alloys possess high strength and manufacturability without operations of thermal treatment (TT). In order to investigate the fabrication possibility of the aluminum boron-containing alloy in the form of sheet rolling with an increased strength without TT, 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 precipitation 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 graphite molds 40 × 120 × 200 mm in size. It is established using computational methods (Thermo-Calc) that manganese forms complex borides with aluminum and zirconium at the smelting temperature; herewith, a sufficient amount of manganese remains in liquid, while zirconium is almost absent. The formation of AlB2Mn2 complex boride is proven; however, the amount of manganese remaining in the solid solution is sufficient to form the particles of the Al20Cu2Mn3 phase in amounts of up to 7 wt %. Boron stimulates the isolation of Al3Zr primary crystals in the alloy with zirconium; in connection with this, an amount of zirconium insufficient for hardening remains in the aluminum solid solution. The possibility of fabricating thin-sheet rolling with a thickness smaller than 0.3 mm with homogeneously distributed accumulations of the boride phase with a particle size smaller than 10 μm is shown. A high strength level (up to 543 MPa) is attained without using quenching and aging due to the precipitation of dispersoids of the Al20Cu2Mn3 phase during hot deformation (t = 450°C).

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).

Effect of Low-Melting Metals (Pb, Bi, Cd, In) on the Structure, Phase Composition, and Properties of Casting Al–5% Si–4% Cu Alloy

The effect of low-melting metals (Pb, Bi, Cd, In) on the structure, phase composition, and properties of the Al–5% Si–4% Cu alloy was studied using calculations. Polythermal sections have been reported, which show that the considered systems are characterized by the presence of liquid regions and monotectic reactions. The effect of low-melting metals on the microstructure and hardening of base alloy in the cast and heat-treated states has been studied.