Influence of dispersoid on mechanical properties of mechanically-alloyed dispersion-strengthened aluminum-based composites

An investigation was undertaken to analyze the mechanical and interfacial properties of a mechanically-alloyed, dispersion-strengthened aluminum + 3 weight percent magnesium matrix as a function of strain rate and temperature. Aluminum-based metal-matrix composites containing either alumina or spinel in nominal 10 and 25 volume fractions were fabricated and tested. Improvements in elastic modulus and coefficients of thermal expansion were noted. An extensive characterization of the composites' microstructure and matrix/oxide interface was performed in order to explain similarities and differences in composite strength and behavior. The strengths which were experimentally determined over a large range of temperature and strain rate in both tension and compression are compared to recent theories pertaining to dispersion-strengthened materials at room and elevated temperatures.Additions of spinel and alumina to an aluminum matrix are shown to significantly improve the strength of the aluminum matrix at both high and low temperatures. Furthermore, additions of the aforementioned oxides are shown to increase modulus of elasticity and decrease coefficients of thermal expansion at the cost of significantly lowering ductility. A reaction zone around alumina particles was observed and analyzed using a high resolution microscope. The reaction zone appears to allow the transfer of strains across the interface which results in a further increase in the modulus and a further decrease in the coefficient of thermal expansion than predicted by standard laws of mixtures.