Assessing Machining Scrap Recycling in Steel and Aluminum Castings

Industry seeks renewable solutions for reducing environmental impacts and increasing efficiency. Machining parts to final shape is the most ubiquitous manufacturing step for metal processing. During machining, scrap material becomes contaminated with cutting fluids and lubricants. The cost of disposing of this scrap is not trivial. In a novel process, machining scrap is compressed into pucks, then electromagnetically heat treated, burning off cutting fluids and lubricants. This enables easy addition of scrap to a melt for recycling. However, using recycled scrap introduces residual elements into the melt, potentially causing microstructural changes, detrimentally impacting material properties. To understand the effects of residual elements, we compared cast samples made with recycled low-carbon steel and aluminum 356 scrap to those made without recycled pucks. Methods included microscopy, composition analysis, and phase analysis. Microstructures were evaluated using visual light microscopy and scanning electron microscopy. Energy Dispersive Spectroscopy was used to determine elemental composition and identify residual elements. Slag from the melt surfaces was analyzed using XRD to determine crystallinity and phase assemblage. Comparing clean and recycled samples allows us to determine the efficacy of the scrap recycling heat treatment and make process improvement recommendations to reduce residual elements' prevalence and impact on material properties.