Evaluation of surface integrity and finish when turning recycled aluminum alloys

This research evaluates the surface integrity and finish of recycled aluminum alloys in turning operations, with a strong emphasis on statistical trends observed in bar chart results. Comparative experiments were conducted on a primary aluminum alloy (EN-AC 43500) and two recycled alloys (EN-AC 43400 and EN-AC 46000) under varying feed rates (0.06, 0.10, and 0.12 mm/rev). Key machining responses—cutting forces, surface roughness parameters, and microstructural alterations—were measured and analyzed. The results show clear trends: cutting forces increased with feed rate for all materials, but the primary alloy consistently exhibited the highest forces while the EN-AC 46000 recycled alloy required the lowest. Similarly, surface roughness worsened with higher feeds yet remained significantly lower (smoother) for the recycled alloys compared to the primary alloy. Notably, EN-AC 46000 achieved the smoothest surfaces across all conditions, whereas EN-AC 43500 showed the highest roughness and pronounced tearing defects at elevated feeds. Microstructural analysis of the machined subsurface revealed corresponding patterns: the thickness of the severe plastic deformation (SPD) layer increased with feed in each material, with the primary alloy developing the thickest deformed layer and more frequent grain distortion. In contrast, the recycled alloys—especially EN-AC 46000—exhibited thinner SPD layers and fewer surface tears. These differences are linked to material composition: the recycled alloys contain hard intermetallic compounds and sludge phase particles that promote brittle chip fragmentation and reduce smearing, thereby lowering cutting resistance and improving surface finish. Overall, the study demonstrates that properly refined recycled aluminum alloys can attain equal or superior machining performance relative to primary alloy, combining excellent surface quality with reduced cutting forces. These findings highlight important relationships between alloy microstructure and machining behavior, underlining the viability of recycled aluminum for high-performance applications and its potential to enhance sustainability in manufacturing without compromising quality or efficiency.