Date of Award

10-5-2017

Degree Type

Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Hu, Henry

Abstract

Mg-based hybrid nano composites (MHNC) reinforced with alumina (Al2O3) fibre and/or micron-sized/nano-sized Al2O3 or AlN particles were successfully prepared by a perform-squeeze casting technique under an applied pressure of 90 MPa. Mechanical properties of unreinforced AM60 alloy, Al2O3 fibre/AM60 composite, hybrid composite containing both Al2O3 fibres and mircon-sized Al2O3 particles, as well as hybrid composite containing both Al2O3 fibres and nano-sized Al2O3 or AlN particles (MHNC) were determined by tensile testing. The addition of fibres and micron-sized particle considerably increases the ultimate tensile and yield strengths of the matrix alloy, despite that a substantial reduction in ductility. Microstructure analyses by optical (OM) and scanning electron (SEM) microscopes show that the homogeneous distribution of reinforcements, clean interfacial structure and grain refinement lead to the high strengths of the composites. The addition of nano-sized Al2O3 or AlN ceramics particles (3 vol.%) into the hybrid composite restores their ductility. The microstructure observation of transmission electron microscopy (TEM) indicates that the presence of a relatively low dislocation density in the matrix grains of the Mg-based hybrid nano composites (MHNCs). The SEM fractography reveals that the fracture of the composites is caused primarily by localized damages, such as particles and fibres damage and cracking, matrix fracture, and interface debonding. The determined tensile properties support the fractographic features.

Share

COinS