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 Сa-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.

No abstract

A comparative analysis of the phase composition and morphology of primary crystals in hypereutectic alloys of the Al–Ca–Ni–X system (where X is Fe, Si, Mn) was carried out by calculation and experimental methods, including the construction of liquidus surfaces. Additional alloying of the base Al–6%Ca–3%Ni alloy with iron and silicon leads to the formation of coarse elongated primary crystals up to 100 μm in length. It was found that the addition of manganese, on the contrary, leads to the formation of relatively small (average size about 20 μm) compact primary crystals of two four-component phases. Presumably, they are phases based on ternary compounds Al9CaNi and Al10CaMn2. The composition of eutectics in quaternary alloys has been determined. All aluminum-calcium eutectics are characterized by a higher proportion of the second phases, a thinner structure compared to the aluminum-silicon eutectic in AK18 silumin, and are also capable of spheroidization upon heating, starting from 500 °C. The combination of compact and spherical particle morphology after annealing  in the 63-2Mn alloy appears to be favorable for deformation. Comparison of the manufacturability of the experimental alloy Al–8%Ca–1%Ni–2%Mn and the grade silumin AK18 showed the advantage of the former. In terms of the totality of its characteristics, the experimental alloy can be considered as the basis for the development of hypereutectic alloys of a new generation as an alternative to piston silumins of the AK18 type. The experimental alloy, the microstructure of which is characterized by a compact morphology and small size of primary crystals and a fine structure of the eutectic, in contrast to hypereutectic silumins, does not require special modification.

No abstract

No abstract