Experimental investigation of microstructural and performance evolution in ultrasonic-assisted stir-cast AA8011-5 wt.% TiB2 composites during multi-pass equal-channel angular pressing

The development of aluminium matrix composites with improved structural and tribological performance has attracted considerable interest for lightweight engineering applications. This work investigates the microstructural, mechanical, tribological, and hot-deformation response of an AA8011 aluminium composite containing 5 wt.% TiB2, fabricated by ultrasonic-assisted stir casting and subsequently processed by equal-channel angular pressing (ECAP). The effect of accumulated severe plastic deformation was evaluated in the as-cast condition and after 2, 4, 6, 8, and 10 ECAP passes. Phase constitution and elemental characteristics were examined using X-ray diffraction and energy-dispersive spectroscopy, while microstructural evolution was characterized using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Repeated ECAP progressively refined the aluminium matrix, improved the spatial distribution of TiB2 particles, and reduced pronounced casting-related structural discontinuities. The EBSD-measured grain size decreased from 12.45 μm in the as-cast condition to 0.54 μm after 10 passes. The resulting microstructural refinement and densification were accompanied by increases in hardness, tensile strength, compressive strength, flexural strength, impact energy, and elongation. The ultimate tensile strength increased from 182 to 266 MPa after 10 passes. Dry-sliding tests performed at loads of 10-50 N and a sliding distance of 5000 m showed reductions in wear rate of approximately 55-58% and in coefficient of friction of approximately 62-75% relative to the as-cast condition. Processing-map analysis further indicated an expansion of the stable deformation region with increasing ECAP passes. The combined results demonstrate that ultrasonic-assisted stir casting followed by multi-pass ECAP provides an effective route for tailoring the microstructure and mechanical, tribological, and hot-deformation response of AA8011-5 wt.% TiB2 composites within the investigated processing conditions.