Processing and Microstructures of δ-Al2O3/ AE44 Composite Synthesized by SS-HPDC

Abstract

A cylinder block with δ-Al2O3/AE44 (Mg4.0Al4.1RE0.3Mn) magnesium matrix composite was manufactured by Slow Shot High Pressure Die Casting (SS-HPDC) technique. The temperature and wall thickness of the fiber added affect its formation. The block is not infiltrated well when the temperature of the preform is below 450°C. Micro-cracks occur if the thickness of the preform is larger than 8.625mm. Microstructures in the AE44 alloy with and without δ-Al2O3fibers (Saffil) were both investigated by means of X-ray diffraction (XRD), optical microscopy (OM) techniques and scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS) equipment. The results show that many Al-RE intermetallic compounds present not only in the matrix but also in the composite, although the grain sizes, the concrete types and their distribution differ. Al-RE second phases in AE44 appear around the grain boundaries in large quantities mainly in globular, lamellar and acicular shape but few in particulate shape, while most of them grow on the fibers in small whiskers and only few scatter in the matrix. Meanwhile, the appearance of Mg2Si in the composite may account for the interfacial reaction between the binder in the preform and the matrix alloy.