Multi-Pass Angular Pressing Refines Microstructure and Strengthens Aluminium Composites

Researchers investigating lightweight engineering materials have demonstrated that applying multi-pass equal-channel angular pressing to an ultrasonic-assisted stir-cast aluminium composite produces marked improvements in microstructural refinement and mechanical performance. The study evaluated an AA8011 aluminium matrix composite reinforced with 5 weight percent titanium diboride particles. By introducing severe plastic deformation through repeated pressing cycles, the investigation tracked progressive modifications in the material across the initial as-cast condition as well as after two, four, six, eight, and ten pressing passes. This experimental work systematically documented the microstructural, mechanical, tribological, and hot-deformation response of the fabricated metal composite.

The composite material was initially synthesized via ultrasonic-assisted stir casting before being subjected to equal-channel angular pressing. The experimental framework evaluated the accumulation of severe plastic deformation across successive processing stages. Through the repeated plastic deformation passes, the processing route achieved a progressive refinement of the aluminium matrix. Additionally, the multi-pass pressing sequence notably improved the spatial distribution of the reinforcing titanium diboride particles throughout the matrix and reduced pronounced casting-related structural discontinuities that formed during primary synthesis.

To evaluate elemental composition and microstructural features across each processing stage, the investigators employed an extensive suite of analytical characterization techniques. The phase constitution and elemental characteristics of the composite were examined using X-ray diffraction and energy-dispersive spectroscopy. Microstructural evolution was characterized through optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Detailed electron backscatter diffraction measurements verified severe grain refinement, revealing that the average grain size decreased from 12.45 micrometres in the as-cast condition to 0.54 micrometres after ten pressing passes.

The resulting structural densification and microstructural refinement were accompanied by broad increases across all evaluated mechanical properties. Testing documented progressive enhancements in material hardness, tensile strength, compressive strength, flexural strength, impact energy, and elongation. Uniaxial tensile evaluations confirmed substantial strengthening of the alloy composite, with the ultimate tensile strength increasing from an initial baseline of 182 megapascals in the as-cast state up to 266 megapascals after the completion of ten equal-channel angular pressing passes.

Tribological behavior and hot-deformation responses also exhibited substantial evolution across the pressing cycles. Dry-sliding wear tests performed under normal loads ranging from 10 to 50 newtons and over an extended sliding distance of 5000 metres demonstrated significant performance improvements compared to the original as-cast condition. The sliding wear rate of the composite was reduced by approximately 55 to 58 percent, while the measured coefficient of friction decreased by approximately 62 to 75 percent. In addition, processing-map analysis showed an expansion of the stable deformation region with increasing pressing passes. Together, these observations demonstrate that combining ultrasonic-assisted stir casting with multi-pass equal-channel angular pressing effectively tailors the structural, tribological, and hot-deformation characteristics of the AA8011 composite within the investigated processing conditions.

Subject of Research: Microstructural and performance evolution of equal-channel angular pressed AA8011-TiB2 composites

Article Title: Experimental investigation of microstructural and performance evolution in ultrasonic-assisted stir-cast AA8011–5 wt.% TiB 2 composites during multi-pass equal-channel angular pressing

Article References: Maddaiah, K. C., Kumar, G. B. V., Agarwal, A., Yelamasetti, B., Anuradha, N., Murali, K., & Wangchuk, D. (2026). Experimental investigation of microstructural and performance evolution in ultrasonic-assisted stir-cast AA8011–5 wt.% TiB2 composites during multi-pass equal-channel angular pressing. PLOS One, 21(10), e0361373. https://doi.org/10.1371/journal.pone.0361373

Image Credits: AI Generated

DOI: 10.1371/journal.pone.0361373

Keywords: AA8011 aluminium alloy, titanium diboride, equal-channel angular pressing, severe plastic deformation, ultrasonic-assisted stir casting, metal matrix composites, grain refinement, electron backscatter diffraction, ultimate tensile strength, dry-sliding wear, coefficient of friction, hot-deformation behavior, processing maps, transmission electron microscopy, X-ray diffraction, energy-dispersive spectroscopy