Investigation of the Constitutive Behaviour and Forming Limits of Recycled Aluminium Alloy Sheet Produced from Urban Scrap in Lagos for Lightweight Vehicle Body Applications

The potential deployment of recycled aluminium alloy sheet from Lagos urban scrap in lightweight vehicle body stamping applications is currently constrained by the absence of characterised constitutive flow behaviour and forming limit data for these materials, which exhibit variable composition and processing history incompatible with the assumptions of forming simulations developed for primary alloy sheet grades, creating a fundamental knowledge gap between scrap metal supply and value-added manufacturing application. This research investigates the constitutive plastic flow behaviour and forming limits of recycled aluminium alloy sheet produced by controlled remelting and rolling of urban scrap collected from Lagos vehicle dismantling markets, Apapa, and Ladipo. Scrap sorting protocols based on portable X-ray fluorescence alloy identification are developed and applied to produce compositionally consistent sheet batches corresponding to approximate AA3000 and AA5000 series equivalents. Uniaxial, biaxial, and plane strain tensile tests are conducted to characterise the full anisotropic yield locus, strain rate sensitivity, and work hardening behaviour of each material batch. Hill's 1948 and Barlat's Yld2000-2d yield criteria are calibrated to the experimental data and implemented in ABAQUS finite element simulations of limiting dome height and cup drawing forming operations. Experimental forming limit diagrams are constructed by Nakajima and Marciniak tests and compared against Marciniak-Kuczynski theoretical predictions. Results demonstrate that compositional variation within a single scrap batch reduces the major principal strain at fracture by up to 22 percent compared to primary alloy benchmarks, quantifying the formability penalty of scrap variability. Keywords: recycled aluminium, constitutive behaviour, forming limits, vehicle body manufacturing, Lagos scrap.