A comparative analysis of the effect of high-pressure torsion (HPT) on the microstructure and tensile properties of the Al–10% La, Al–9% Ce, and Al–7% Ni model binary eutectic aluminum alloys is carried out. An HPT of 20-mm diameter specimens in as-cast state was carried out under constrained conditions, at room temperature, pressure P = 6 GPa, and number of turns N = 5. It is shown that the formation of nano- and submicrocrystalline structures and the refinement of eutectic particles in aluminum alloys simultaneously provide a multiple increase in strength while maintaining a high plasticity margin. This combination of properties has been achieved for the first time for severely deformed binary aluminum eutectics. The relationship between the type of eutectic particles, the structure formation process and the mechanical properties of the aluminum alloys has been established. The thermal stability of severely deformed aluminum alloys at heating up to 200 °C has been studied.

Calcium is one of the most widespread and, consequently, low-cost metals on Earth. It has been applied for a long time in modifying and alloying alloys of heavy metals, in particular, lead and...

In the present paper, Natural Metal-Matrix Composites (NMMC) based on multicomponent hypereutectic Al-Ca-(Mn)-(Ni) alloys were studied in as-cast, annealed and rolled conditions. Thermo-Calc software and microstructural observations were utilised for analysing the equilibrium and actual phase composition of the alloys including correction of the Al-Ca-Mn system liquidus projection and the solid phase distribution in the Al-Ca-Mn-Ni system. A previously unknown Al₁₀CaMn₂ was discovered by both electron microprobe analysis and X-ray studies. The Al-6Ca-3Mn, Al-8Ca-2Mn, Al-8Ca-2Mn-1Ni alloys with representative NMMC structure included ultrafine Ca-rich eutectic and various small-sized primary crystals were found to have excellent feasibility of rolling as compared to its hypereutectic Al-Si counterpart. What is more, Al-Ca alloys showed comparable Coefficient of Thermal Expansion values due to enormous volume fraction of Al-based eutectic and primary intermetallics. Analysis of tensile samples’ fracture surfaces revealed that primary intermetallics may act either as stress raisers or malleable particles depending on their stiffness under deformation. It is shown that a compact morphology can be achieved by conventional casting without using any refining agents. Novel hypereutectic Al-Ca NMMC materials solidifying with the formation of Al₁₀Mn₂Ca primary compound have the best ductility and strength. We reasonably propose these materials for high-load pistons.

The phase transformations in the Al-Ca-Mg-Si system have been studied using thermodynamic calculations and experimental methods. We show that at 10% Magnesium (Mg), depending on the concentrations of calcium (Ca) and silicon (Si), the following phases crystallize first (apart from the aluminum (Al) solid solution): Al₄Ca, Mg₂Si, and Al₂CaSi₂. We have found that the major part of the calculated concentration range is covered by the region of the primary crystallization of the Al₂CaSi₂ phase. Regardless of the Ca and Si content, the solidification of the aluminum-magnesium alloys ends with the following nonvariant eutectic reaction: L → (Al) + Al₄Ca + Mg₂Si + Al₃Mg₂. With respect to the temperature and composition of the liquid phase, this reaction is close to the eutectic reaction in the Al-Mg binary system. The addition of Ca and Si to the Al-10% Mg base alloy increases its hardness, reduces its density, and has no negative influence on its corrosion resistance. We have also established that the near-eutectic alloy containing about 3% Ca and 1% Si has the optimum structure.

This study investigated the eutectic alloys based on aluminum containing small amount of rare earth metals (REM): Al – 6Ca – 3Ni – 2Ce; Al – 6Ca – 3Ni – 2La; Al – 6Ca – 3Ni – 2Pr. The compositions of the alloys were selected on the basis of previous studies of ternary Al – Ca – Ni and Al – Ni – Ce systems, taking into account the similarity of the structure of the Al – REM binary systems. Melting was carried out in an induction furnace by RELTEC. Alloys were prepared on the basis of aluminum A99. Annealing of the samples at 550 оC for three hours was carried out in SNOL 8.2/1100 and SNOL 58/350 muffle electric furnaces. Calculation of Al – Ca – Ni – Ce systems at 6% Ca by means of Thermo-Calc (databases TTAL5, TCAL4), showed that primary crystals of the Al3Ni phase should be formed in the alloys of the selected compositions, however these crystals were not present. Using optical and scanning electron microscopy, the structure of alloys in the as-cast and heat-treated states was studied. It is established that in the process of non-equilibrium crystallization, the boundary of the phase region of existence of the aluminum solid solution significantly expands. Using micro-X-ray spectral analysis (MRSA), it was determined that during the equilibrium crystallization conditions in the Al – Ca – Ni – Ce system, rather than the binary Al3Ni the ternary Al9Ni2Ca phase is formed. The possibility of applying hot rolling to Al – Ca – Ni based alloys additionally alloyed with Ce, La and Pr has been established, and the mechanical properties of hot-rolled samples have been obtained. Hot rolling was carried out at 500 oC. Rolling was carried out in five passes, the total degree of deformation in all cases was about 70%. Samples of the Al – 6Ca – 3Ni – 2Ce alloy were additionally rolled at a temperature of 550 oC. On the basis of a comparison of the mechanical properties and the microstructure of rolled products, it is assumed that the best mechanical properties are possessed by the samples of those alloys in which intermetallics have the smallest dimensions and are most evenly distributed in an aluminum solid solution. In particular, this demonstrates the Al – 6Ca – 3Ni – 2La alloy rolled at 500 oC and the Al – 6Ca – 3Ni – 2Ce alloy rolled at 550 oC. This work was supported by Task No. 11.2072.2017/4.6 for the implementation of the project on the theme of “Development of technology for obtaining deformed semi-finished products from alumomatrix eutectic composites reinforced with L12 nanoparticles without hardening”.