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 2.5μm at higher temperatures consistent with superplastic behaviour. Typically each oxide fibre had a diameter of 200nm and consisted of nanocrystalline MgO and MgAl 2 O 4 grains of 4.5±0.7nm 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.