Enhanced Young’s Modulus of Al-Si Alloys and Reinforced Matrices by Co-continuous Structures

Abstract

In the present work, the elastic behavior of different hypoeutectic and hypereutectic Al-Si alloys and different Al₂O₃ short fiber and SiC particle reinforced materials (SFRM and PRM, respectively) is studied. The effective Young’s modulus (E) of materials was experimentally measured and compared with the different theoretical predictions of Hashin-Strikman, Tuchiniskii, shear lag, and the rule of mixtures (ROM). The unreinforced alloys present an interconnected lamellar Si structure after fast solidification, which increases the Young’s modulus up to that of the Tuchiniskii prediction for interpenetrating skeletal structures. On the other hand, alloys presenting isolated and coarse Si particles (after spheroidization treatment at 540°C) are well described by the lower bound of the ROMs. Similarly, the interconnected Si-SiC structure observed in 10 and 70 vol% SiC reinforced AlSi7Mg and AlSi7 matrices in the as cast condition is responsible for the higher stiffness of the composite, if compared with that of Al99.5 or spheroidized AlSi7 matrices. An analogous behavior is observed in the SFRMs in the as cast condition, where the Si lamellae bridge the Al₂O₃ fibers, increasing the Young’s modulus of the composites, if compared with the conditions of spheroidized Si. Furthermore, the primary Si particles produce an improvement in the Young’s modulus by connecting several fibers in the case of a short fiber-reinforced hypereutectic AlSi18 matrix.