Comparison of the Effect of Ni, Mn, Fe, and Si Additives on the Microstructure and Phase Composition of Hypereutectic Aluminum-Calcium Alloys

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) has been 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 mu m in length. It is found that the addition of manganese, on the contrary, leads to the formation of relatively small (average size about 20 mu m) 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 and a thinner structure compared to the aluminum-silicon eutectic in AK18 silumin, and they are also capable of spheroidization upon heating, starting from 500 degrees C. The combination of compact and spherical particle morphology after annealing in the 63-2Mn alloy appears to be favorable for deformation. A comparison of the manufacturability of the experimental Al-8% Ca-1% Ni-2% Mn alloy and AK18 grade silumin shows the advantage of the former. In terms of the totality of its characteristics, the experimental alloy can be considered the basis for the development of new-generation hypereutectic alloys 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, unlke hypereutectic silumins, does not require special modification.