Microstructural analysis and hardness of aluminum composites reinforced with nickel ferrite consolidated by extrusion at different temperatures

Full text: Powder metallurgy is one of the main processing routes for the production of metal matrix composites reinforced with ceramic particles. In this study, aluminum matrix composite powders with nickel ferrite reinforcement were processed. Atomized aluminum powder with 99.5% purity (wt%) and nickel ferrite powder synthesized by the Pechini method were used to produce the composite powder by high energy milling. Two compositions in amounts of 0.5% and 2.0% (wt%) of nickel ferrite were mixed with aluminum powder and milled during 5h in a SPECX high energy mill, with a ball-to-mass ratio of 10:1 by weight. Both composite powders were cold pressed at 25°C and consolidated by extrusion at the temperatures of 400°C and 425°C, resulting in four distinct cylindrical ingots of 3 mm in diameter. The microstructure of the ingots was analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The XRD analysis showed the presence of two phases (alpha aluminum and nickel ferrite) in the composite powders prepared through the milling process and the SEM analysis showed a regular distribution of nickel ferrite in the aluminum matrix. By the samples consolidated at 400 deg C, the use of 2.0% of nickel ferrite promoted an effective increase of 16% in the Vickers hardness relative to the 0.5% nickel ferrite sample. However, the consolidation at 425°C promoted a negligible difference of 2.0% in hardness between the samples. It can be concluded that the extrusion at 400°C was dominated by the hardening mechanism of reinforcement particles, while the extrusion at 425°C possibly presented an equilibrium between the hardening mechanisms of reinforcement particles and a softening mechanism grain grown. (author)