Enhanced fatigue life of additively manufactured high-strength TiB2-reinforced Al-Cu-Mg-Ag composite through in-process surface modification during hybrid laser processing

Laser powder bed fusion (L-PBF), an additive manufacturing (AM) technique, often leads to parts with high surface roughness in as-built condition, hence limited fatigue performance. This paper showcases the favourable impact of applying an in-process surface modification, adopting a hybrid laser processing technique (dual-laser PBF (dL-PBF)), on the three-point bending fatigue life of TiB2-reinforced Al-Cu-Mg-Ag composite coupons. The dL-PBF process parameters are optimised for this high-strength aluminium-based metal matrix composite, followed by a comparative study between 3 surface conditions, i.e. as-built, dL-PBF processed, and milled, focusing on surface roughness, concomitant stress concentration factor, surface residual stress, sub-surface hardness, sub-surface microstructure, and fatigue performance. While no significant hardness or microstructural differences are found, surface roughness and stress concentration factor are substantially decreased (> 50%) and identified as the primary factors for the significantly enhanced fatigue performance of dL-PBF processed TiB2-reinforced Al-Cu-Mg-Ag composite parts with up-facing inclined surfaces.