A quantitative study of cavity development in the tensile testing of an aluminum metal matrix composite processed by equal-channel angular pressing

A metal matrix composite, consisting of an Al-6061 matrix alloy reinforced with 10 vol.% of fine Al2O3 particulates, was processed by equal-channel angular pressing for 1 pass at room temperature and an additional 11 passes at 473 K. Microstructural observations showed the grain size was reduced from ∼3.5 to ∼1.9 μm but the average particulate size remained unchanged at ∼270 nm. Tensile testing was conducted to failure at 873 K on samples cut from the as-received material and from as-pressed billets. Following fracture, quantitative measurements were taken to determine the size and shape of the internal cavities developed during tensile testing. The measurements show cavities form more readily in the as-received condition probably due to the higher flow stresses in this material. The pressed material contained several large cavities oriented parallel to the tensile axis. Calculations show these cavities are consistent with a transition from superplastic diffusion growth to plasticity-controlled growth.