Effects of Mechanical Milling Time and Boron Carbide Reinforcement Content on Powder and Hot Extruded Al-2wt.%Cu-B4C Nanocomposites: Microstructural, Mechanical and Fracture Characterization

The main objective of this study is an investigation on influences of mechanical milling time and B4C reinforcement content on microstructure and mechanical properties of powder and hot extruded B4C reinforced Al-2wt.%Cu aluminum alloy matrix nanocomposites. These composites were fabricated through mechanical milling, cold isostatic pressing and hot extrusion processes. Results of powder characterization showed that steady-state time of mechanical milling was predicted to be around 20h. Microstructural analyses of Al-Cu-4wt.%B4C composite powder revealed that strain-induced dissolution of fine B4C reinforcements and in situ formation of Al3BC phases within the nanocrystalline aluminum matrix were detected only when the composite powder was subjected to at least mechanical milling time of 20h and subsequent heat treatment. Strength and hardness of the nanostructured samples were significantly improved by increasing mechanical milling time and B4C reinforcement weight percent due to higher level of severe plastic deformation applied to the powders during the fabrication process.