Improving the tribological characteristics of aluminum 6061 alloy by surface compositing with sub-micro-size ceramic particles via friction stir processing

This study presents a solid state surface engineering technique for forming a composite surface layer on aluminum to improve surface hardness and wear resistance without sacrificing the ductility and conductivity of the bulk. Friction stir processing (FSP) was used to stir and mix sub-micro-size Al2O3 and SiC particles into the surface of an aluminum 6061-T651 alloy plate to form an composite layer of up to 3 mm thick. The concentration of the hard phase was in the range of 20–30 vol.%. Compared with a non-processed aluminum surface, the FSP-formed composite surface exhibited substantial friction and wear reductions by 40% and 90%, respectively, when rubbed against a bearing steel. Post-FSP heat treatment afforded further enhancement of the wear resistance. Transmission electron microscopy revealed high matrix dislocation density in the composite surface that is believed to be largely responsible for such significant properties improvements.