Role of knurled surface topography of IS2062 steel in influencing the mechanical integrity and microstructural evolution of friction-surfaced AA6061 coatings

Friction surfacing as a promising coating technology in solid-state method enables the development of defect-free, metallurgically bonded coatings for dissimilar material combinations. This study investigates the influence of engineered knurled surface topographies (L10, S10, R12, R20, L22, S24) on the interfacial bonding, microstructural evolution, and performance of AA6061 T6 coatings deposited on IS2062 steel. Push-off testing revealed a maximum bonding strength of ∼15.4 kN for the R20 pattern, indicating optimal mechanical interlocking and heat generation, whereas coarse and fine patterns exhibited comparatively lower strengths of 10.8–13.3 kN. Microstructural characterization using SEM and FESEM confirmed dense, defect-free coatings with refined grains due to dynamic recrystallization, while EDX analysis indicated ∼63 wt.% Al and ∼32 wt.% Fe with a thin diffusion layer. XRD confirms stable FCC-Al and BCC-Fe phases with suppressed brittle intermetallics, ensuring a structurally sound coating. AFM analysis revealed a uniform nanoscale morphology with ∼86 nm height variation. A graded microhardness profile with peak strengthening at the interface was observed. Corrosion studies demonstrated enhanced performance with higher polarization resistance (42.21 kΩ) and protective passive behavior. Overall, optimized knurled topography significantly enhances coating integrity and functional performance.