Synthesis of Nanocrystalline Al6061/Al2O3 Nanocomposite via in-situ Solid-Gas Reaction during High-Energy Mechanical Milling

Mechanical milling has been widely used to produce nanocrystalline materials because of its simplicity and applicability to synthesize most metals, alloys and intermetallics as well as metal matrix nancomposites (MMNCs) [1]. The process of mechanical milling consists of repeated welding-fracturing-welding of a mixture of powder particles in a high-energy ball mill. Nano-sized particles can be finely dispersed through the metal matrix by reaction between the milling atmosphere and the powder mixture during milling, leading to in-situ fabrication of MMNCs. The advantages of the in-situ fabrication compared with the ex-situ methods (addition of reinforcement to metal matrix) are dealing with more stability and stronger interfacial bonding between the reinforcement particles and matrix, more uniform distribution of ultrafine particles in the matrix, and relatively lower processing cost [2]. The aim of the present work is to fabricate nanocrystalline Al6061 matrix nanocomposite through controlling of the reaction between the aluminum matrix and the milling atmosphere containing prescribed amount of oxygen. The effect of the gas-solid reaction on the grain refinement is presented. The morphological changes of the powder particles during the reactive milling are addressed