High temperature deformation and fracture of tribo-layers on the surface of AA5083 sheet aluminum–magnesium alloy

Plastic deformation and fracture of tribo-layers covering surfaces of aluminum AA5083 alloy sheets subjected to tensile tests at elevated temperatures and different strain rates were studied. When tested at 420 °C and a strain rate of 4 × 10−2 s−1, tribo-layers failed predominantly by brittle fracture but about 10% of the fractured oxide patches were found to be held together by fibrous structures. These fibres maintained uniform cross-sections and were as long as 2.5 μm at higher temperatures consistent with superplastic behaviour. Typically each oxide fibre had a diameter of 200 nm and consisted of nanocrystalline MgO and MgAl2O4 grains of 4.5 ± 0.7 nm in diameter as revealed by high resolution TEM. It was suggested that a Coble type creep was responsible for the superplasticity of the oxide fibres.

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► Fibre formation in the tribo-layer of an AA5083 alloy subjected to high temperature deformation.
► Characterization of fibres’ structure using FIB and HRTEM.
► Diffusional flow prompted by nano-size grains was responsible for superplasticity in fibre.