The Effect of Composition, Geometry and a Novel Tool Design on Metal Recovery During Aluminum Process Scrap Remelting

Abstract

Aluminum recycling requires less energy and releases fewer greenhouse emissions than primary production from naturally occurring ores; however, a significant fraction of the furnace charge is lost to dross generation during remelting. In this article, we use an electric furnace to remelt clean aluminum sheet and machining chip process scrap of varying thickness, surface roughness, and composition. The metal recovery results show that magnesium-containing alloys (e.g., 2xxx, 5xxx, 6xxx, and 7xxx alloys) accelerate dross generation and lower metal recovery. This is likely due to magnesium having a higher reactivity than aluminum, with the magnesium content detected in the dross (using Energy-dispersive X-ray spectroscopy) greater than the magnesium content in the alloy. Metal recovery decreased when remelting thinner scrap. Metal recovery for clean machining chips was lower than for aluminum sheet scrap of the same thickness and composition. This disparity was likely due to the greater surface roughness of the machining chips, which will increase the surface area for oxidation and potentially the wetting of the oxide by the Wenzel effect. The decreased metal recovery for scratch brushed aluminum sheets confirmed the effect of surface roughness. Subsequently, a “squeeze” cutting tool was designed and manufactured, which smooths the otherwise rough back-side of the machining chips. These smoother machining chips exhibited increased metal recovery during remelting.