Multi-step surface treatment of AA-2024-T3 produces failure mode transition and interfacial strengthening in carbon fiber aluminum laminates

Fiber metal laminates are limited by the metal–composite interface, and in carbon fiber aluminum laminates (CARALL) the aluminum surface condition governs how much load that interface carries before it delaminates. This study establishes how a multi-step treatment of AA-2024-T3, comprising mechanical abrasion, NaOH alkaline etching, HNO 3 acid desmut and sulfuric acid anodization (SAA; 15 wt.% H 2 SO 4 , 20 V DC, 45 min), changes the interfacial failure mechanism and the mechanical response that follows. Two routes were examined, viz. vacuum-bagged woven carbon fabric with epoxy (E-type) and compression-molded unidirectional carbon fiber with adhesive film (A-type), each in (2/1) and (3/2) configurations, assessed by tensile, T-peel, short-beam shear and three-point flexure tests at n = 3 per condition. Treatment increased T-peel load by 758% (A-type) and 789% (E-type), apparent interlaminar shear strength by 123–351%, and flexural strength by 274–386%; every interface-dominated comparison reached p ≤ 0.0026 with no overlap between individual specimen values. Tensile strength rose 9–11%, which was not significant at n = 3. Quantitative fractography identified the governing change: adhesive separation gave way to mixed adhesive–cohesive fracture, with resin infiltrating the cavities produced by treatment. The improvements reflect the complete sequence, not SAA alone.