Material Characterisation of Recycled Aluminium Alloy Castings from Automobile Scrap in Lagos Metal Markets

The informal recycling of aluminium scrap from end-of-life vehicles constitutes a significant low-technology manufacturing activity in urban Lagos, yet the mechanical and compositional consistency of resulting castings is rarely characterised to engineering standards. This study investigates the chemical composition, microstructure, and mechanical properties of aluminium alloy castings produced by artisan foundries in Ladipo and Alaba International markets, Lagos State. Samples were collected from six foundries using sand casting and gravity die casting methods. Chemical composition was determined by optical emission spectrometry, and microstructural analysis was conducted using scanning electron microscopy and energy-dispersive X-ray analysis. Tensile strength, hardness, and elongation were measured following ISO 6892 and ISO 6506 standards. Results revealed significant variation in silicon, copper, and iron content across foundries, reflecting inconsistencies in scrap sorting and blending practices. Mean tensile strength ranged from 112 to 178 MPa across sampled foundries, with hardness values between 55 and 82 HRB. Microstructural examination identified porosity, shrinkage defects, and eutectic silicon morphologies consistent with unmodified Al-Si alloys. The study concludes that with improved scrap sorting and controlled melting practice, recycled aluminium castings from the Lagos informal sector can meet strength requirements for non-critical automotive and general engineering applications. Keywords: recycled aluminium, sand casting, material characterisation, Lagos foundries, alloy composition.