Enhanced properties of Mg-based nano-composites reinforced with Al2O3 nano-particles

In this study, 0.5, 1 and 2 wt.% of alumina nano-particles were added to pure Mg and AZ31 magnesium alloy via a stir-casting method. A uniform distribution of the Al2O3 nano-particles with an average diameter of 100nm, refined the grain structure of the cast materials and decreased the coefficient of thermal expansion (CTE), thus improving the dimensional stability of both pure magnesium and AZ31 alloy. The addition of 2 wt.% nano-Al2O3 particles showed great potential in the reduction of CTE from 27.9 to 25.9 x 10(-6) K-1 in pure Mg, and from 26.4 to 25.2 X 10(-6) K-1 in AZ31. Some of the cast samples were hot rolled and annealed to investigate the pinning effect of nano-particles on the recrystallization and subsequent mechanical property behavior. Characterization of mechanical properties revealed that the presence of nano-particles significantly increased yield stress and tensile strength but decreased the ductility of both pure magnesium and AZ31. The yield stress and tensile strength both increased by 40 MPa in the Mg-2Al(2)O(3) nano-composite, whereas this improvement was about 65 MPa for AZ31-2Al(2)O(3). The yield strength improvement was mostly due to the CTE mismatch between the matrix and the particles, and to a lesser extent to the Orowan and Hall-Petch strengthening mechanisms. The contribution of each of these mechanisms was used in a modified shear lag model to predict the total composite-strengthening achieved. Examination of fracture surfaces showed that the relatively ductile fracture of the monolithic materials changed to a more brittle mode due to the presence of nano-Al2O3 particles. (C) 2009 Elsevier B.V. All rights reserved.