Process–surface–performance relationship in WAAM-fabricated AlSi5: functional surface engineering through topographical and chemical modification

Abstract

Wire arc additive manufacturing (WAAM) of aluminum alloys often produces components with complex surface morphologies that directly influence functional performance. In this study, the effect of surface condition on the wettability, surface energy and hardness of WAAM-fabricated AlSi5 was systematically investigated without relying on microstructural analysis. Three surface states; as-built, mechanically polished and NaOH-etched were evaluated. The as-built surface exhibited high roughness (Ra = 38.6 ± 5.1 µm), a peak-dominated morphology (Rsk = + 0.85) and hydrophobic behavior (water contact angle ≈98°), resulting in low surface energy (∼28.5 mJ m−2). Mechanical polishing significantly reduced surface roughness ( Ra=1.2±0.3μm), which eliminated roughness-induced indentation artifacts and led to more reliable and higher apparent hardness values ( 61±3 HV0.1) with improved uniformity, without altering the intrinsic material hardness. In contrast, NaOH etching introduced controlled micro-texturing (Ra = 4.7 ± 0.8 µm) and yielded the highest wettability (θ ≈64°) and surface energy (∼47.8 mJ m−2). A key finding is that wettability cannot be described by roughness amplitude (Ra) alone; higher-order parameters such as skewness (Rsk) and kurtosis (Rku), together with surface chemistry, play a decisive role. Statistical analysis confirmed that surface condition significantly affects hardness (p < 0.001). Unlike conventional WAAM studies that primarily focus on microstructural characterization, this study proposes a surface-functionality-oriented framework for WAAM AlSi5 where functional performance is directly evaluated through roughness statistics, wettability, surface energy and hardness. This approach demonstrates that application-relevant surface behavior can be effectively tailored and predicted without relying on extensive microstructural analysis.