Facile Synthesis of Al-20Si@Al2O3 Nanosheets Composite Powders and Its Refinement Performance on Primary Silicon in Al-20Si Alloy

Abstract

In this work, Al(OH)3 nanosheets are synthesized in situ on the surface of an Al-20Si alloy via the water bath method, and Al–20Si@Al2O3 composites are then obtained after calcination. The growth mechanism of the Al(OH)3 nanosheets is revealed, and a pathway is demonstrated to obtain Al–20Si@Al2O3 nanosheets with the desired structure and thickness. Furthermore, the influence of different Al–20Si@Al2O3 contents on the primary silicon phase in the Al–20Si alloy is investigated, and the mechanism of such an influence is theoretically analyzed. The mechanical properties of the modified Al–20Si alloy are tested, and the effects of the morphology and particle size of the silicon phase on the alloy properties are studied. The results show that Al–20Si@Al2O3 synthesized in situ by water bath has good dispersion in the melt. There is a lot of γ-Al2O3 dispersed in the matrix of the alloy, and the primary silicon of the Al-20Si alloy is obviously refined. By increasing the content of the modifier, the average size of primary silicon decreases first and then increases. When 15 wt% of the modifier is added, the refinement effect of primary silicon reaches its peak, and the size of primary silicon is reduced from unmodified 86.4 μm to 28.5 μm. The hardness and tensile strength of 75.2 HB and 120.3 MPa are increased to 107.2 HB and 185.9 Mpa by 42% and 55%, respectively. Compared with adding γ-Al2O3 directly, this experiment provides a simple method to synthesize the modifier, and γ-Al2O3 can be dispersed evenly in the aluminium-silicon alloy melt more easily by in-situ generation, without ultrasonic treatment or other ways. During mass production, the cost can be better controlled and good results can be achieved at the same time.