Centrifugally cast Zn–27Al–xMg–ySi alloys and their in situ (Mg2Si + Si)/ZA27 composites

Effects of composition, mold temperature, rotating rate and modification on microstructure of centrifugally cast Zn–27Al–xMg–ySi alloys have been investigated. In situ composites of Zn–27Al–6.3Mg–3.7Si and Zn–27Al–9.8Mg–5.2Si alloys were fabricated by centrifugal casting using heated permanent mold. These composites consist of three layers: inner layer segregates lots of blocky primary Mg2Si and a litter blocky primary Si, middle layer contains without primary Mg2Si and primary Si, outer layer contains primary Mg2Si and primary Si. The position, quantity and distribution of primary Mg2Si and primary Si in the composites are determined jointly by alloy composition, solidification velocity under the effect of centrifugal force and their floating velocity inward. Na salt modifier can refine grain and primary Mg2Si and make primary Mg2Si distribute more evenly and make primary Si nodular. For centrifugally cast Zn–27Al–3.2Mg–1.8Si alloy, the microstructures of inner layer, middle layer and outer layer are almost similar, single layer materials without primary Mg2Si and primary Si are obtained, and their grain sizes increased with the mold temperature increasing.