Preparation and characterization of AZ91E/Al2O3 composites using hybrid mechanical and ultrasonic particle dispersion

Abstract

As a light structural metal, magnesium (Mg) has been gaining increasing popularity in the transportation sector. However, widespread implementation of Mg is hindered by its low mechanical properties compared to aluminum and steel. A proven method to improve the mechanical properties of cast alloys is grain refinement. A finer grain size can be achieved through the addition of particle substrates to the liquid melt, where they can act as nucleation sites for the formation and growth of grains. Inoculants are typically added to the molten metal and dispersed using mechanical stirring (MS) with an impeller. However, achieving uniform dispersion of inoculants using this method is challenging. Alternatively, researchers have been investigating the potential of ultrasonic treatment (UST) to supplant MS. In this study, the dispersion of Al2O3 particle inoculants in AZ91E Mg alloy was investigated. Cast AZ91E + Al2O3 composites were prepared using MS or UST. The microstructure of the resultant castings were characterized using optical microscopy and scanning electron microscopy, while mechanical properties were evaluated through ambient temperature tensile tests and theoretical models. The specimens treated with UST displayed improved mechanical properties relative to the base alloy and the samples prepared with MS. This was attributed to the finer grain size, thermal expansion mismatch between the refiner and the matrix and improved inoculant distribution within the sonicated samples. This research resulted in a unique correlation between theoretical strengthening mechanism prediction models and experimental results achieved through sonication and grain refinement. Therefore, advances in the preparation of cast alloys and implementation of critical innovative technologies such as UST can improve the mechanical properties of Mg alloys.