Structural and physicomechanical properties of directionally crystallized aluminum-silicon alloys

Aluminum-silicon alloys (from 8 to 25 wt% Si) have been prepared by directional crystallization of shaped samples by the Stepanov growth at a solidification rate of 10$^3$ $\mu$m $\cdot$ s$^{-1}$. The dependences of the microhardness, Young’s modulus, internal friction, yield stress, and ultimate tensile stress of the alloys on the silicon content have been studied. It has been shown that the ultimate tensile stress has a maximum, and the yield stress has a kink at 15 wt% Si; the composition corresponds to the eutectic composition at the solidification rate used. The silicon content in the eutectics increases with an increase in the solidification rate. The increase in the ultimate tensile stress is explained by an increase in the volume fraction of the more strength fine-crystalline structure of the eutectics as a result of the decrease in the volume fraction of more plastic dendrites of the primary crystals of the $\alpha$-Al solid solution. The decrease in the ultimate tensile stress of the hypereutectic alloy is determined by the increase in the volume fraction of brittle primary silicon crystals of various shapes.