Microstructure and Properties of A6061-T6 Aluminium Alloy after Ultrasonic Nanocrystal Surface Modification

A severe plastic deformation (SPD) layer on the surface of A6061-T6 aluminum alloy was obtained by ultrasonic nanocrystal surface modification (UNSM) technique at static loads of 15 N and 30 N. The microstructure from surface to matrix was examined using optical microscopy, scanning electron microscopy and X-ray diffraction. Fatigue performance of the alloy was also studied by fatigue testing. The results show that the deep of SPD layer, surface hardness and surface residual compressive stress increased with the increase of static load. After being treated by UNSM technique, the surface roughness of samples declined, and the surface microstructure were isometric and random oriented nano-crystals. The fatigue fracture of A6061-T6 after UNSM showed the shearing crack initiation mechanism instead of typical subsurface facet or micro-void initiation mode before UNSM.