The effect of near net-shape manufacturing variables in the corrosion and mechanical properties of aluminum/mullite nanocomposites

Near net-shape processing of aluminum/mullite hybrid materials was conducted and their improved properties through interfacial manipulation were studied. The aluminum/mullite nanocomposites were produced via high energy ball milling in stainless steel and nylon media, followed by consolidation with Hot Isostatic Pressing (HIP). Samples milled in stainless steel were susceptible to intergranular corrosion due to the depletion of trace metals (impurities) segregated at the grain boundaries. Samples milled in nylon were less susceptible to intergranular corrosion due to carbon impurities segregated at the grain boundaries, thereby preventing the initiation of cracks and corrosion of the aluminum matrix. Corrosion rates for samples containing aluminum only were 70.35 and 9.39 mpy when milled in stainless steel and nylon respectively, and corrosion rates for the nanocomposites containing 30% mullite were 40.5 and 6.3, respectively. The room temperature flexural moduli of nanocomposites containing 30% mullite were 128--130 GPa---an increase of 116% over unreinforced, commercial, cast aluminum. Room temperature moduli were independent of milling media type; at higher temperatures the flexural moduli of nanocomposites milled in nylon were 50% higher than those milled in stainless steel. The difference is due to the type of impurities imparted during mechanical attrition. The presence of carbon from nylon in the intergranular regions improves corrosion and mechanical properties.