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Tetrahedral amorphous carbon (ta-C) coatings are widely applied in machining aluminum alloys to suppress adhesion and wear. However, further improvements in anti-adhesion properties and coating adhesion strength are required under severe cutting conditions. In this study, Ta-doped DLC (ta-C:Ta) coatings with varying Ta contents were prepared and evaluated through cutting tests on ADC12 aluminum alloy, tribological measurements, and adhesion strength tests. Increasing Ta content led to higher friction coefficients and specific wear rates, whereas scratch adhesion tests showed improved critical load associated with reduced residual compressive stress. Among the tested coatings, ta-C:Ta1.1 exhibited the best performance, demonstrating reduced tool wear and lower cutting forces compared with undoped ta-C and higher-Ta coatings. This superior durability is attributed to a favorable balance between high hardness and relaxed compressive stress. The presence of dispersed TaC nanocrystals further suggests enhanced crack resistance, indicating that controlled nanoscale Ta doping is a promising route to achieve both hardness and toughness in ta-C coatings. • Cutting tests revealed that ta-C:Ta1.1 (1.1 at% Ta) exhibited the best combination of wear resistance and low cutting resistance during drilling of aluminum alloys. • Friction and wear tests indicated that increased Ta content raised friction coefficient and specific wear rate. • Scratch tests showed improved adhesion strength with higher Ta content, correlating with reduced residual compressive stress. • Ta-doped coatings exhibited smaller delamination areas, implying enhanced crack resistance due to dispersed TaC nanocrystals. • Superior performance of ta-C:Ta1.1 was attributed to the balance between hardness, improved adhesion, and microstructural toughening.