Influence of Friction Stir Additive Manufacturing Parameters on Dry Friction and Wear Properties of Al–Mg–Si Alloy's Built Surfaces Fabricated by Sheet Lamination

Abstract

In this article, friction stir additive manufacturing, a solid-state process for rapid fabrication of large components, is employed to investigate laminated Al–Mg–Si alloy blocks. The study delves into microstructural changes, hardness distribution, and wear behavior on two distinct surfaces using various parameters such as rotational speed (800 rpm and 1200 rpm), traverse speed (41 mm/min and 82 mm/min), and a 50% pin overlap for block fabrication. Macrographs demonstrate the influence of adjacent toolpath overlap on layer integrity through interfacial mixing and consolidation of plastically deformed material. Within the overall stirred zone, re-stirring effects lead to refined grain formation and the dissolution of Mg2Si precipitates, resulting in an uneven micro-hardness distribution due to varying thermal cycles. Notably, specimens with a traverse speed of 41 mm/min exhibit reduced wear loss, attributed to microstructural changes that enhance resistance to plastic deformation during sliding, thereby improving tribo-layer stability. This enhancement is attributed to increased hardness arising from refined grains and the strain-hardening effect. Interestingly, the study finds that the horizontal surface of the fabricated blocks displays superior wear resistance compared to the vertical surface, due to the more homogeneous microstructure in individual layers. Further analysis using field emission scanning electron microscope and energy dispersive X-ray spectroscopy unveils the presence of glaze layers, oxide films, galling surfaces, grooving, trimming impacts, plowing marks, and the accumulation of wear debris within wide pits and on worn-out pin surfaces. Scar morphology reveals that both abrasive and adhesive wear mechanisms contribute to volumetric losses in the specimens.