Eco-Friendly Optimization of Fatigue Strength in Sand-Cast Aluminium Alloys Using Waste Metal Chips as Mold Additives

Abstract

This study investigates the enhancement of fatigue strength in aluminium alloy castings obtained from scrap engine blocks, through grain refinement achieved by incorporating metal chips into sand molds during sand casting. The materials used included a scrap engine block (aluminum alloy), molding sand, and chips from cast iron and brass, all of which were procured and characterized. Using a Taguchi design of experiment, alloys were cast with varying proportions of particle sizes and amounts of brass and cast iron chips. XRF analysis identified aluminium (76.61%), silicon (17.49%), and magnesium (1.28%) as the primary elements in the scrap aluminium alloy, while brown sand predominantly contained silicon (89.51%) and phosphorus (7.41%). The cast iron was mainly composed of iron (88.3%), carbon (3.7%), and silicon (2.3%). Fatigue testing results indicated a 24.78% increase in strength compared to the as-cast alloy, with Taguchi optimization yielding a further improvement of 28.30%. The optimal configuration found included brass/cast iron metal chips at level 2, a chip content of 40 %wt (level 4), and a chip particle size of 100 µm (level 1), resulting in a fatigue strength of 70.58 MPa. SEM and optical micrographs of the optimal sample showcased a finer grain structure. Thermogravimetric analysis revealed a 3.01% reduction in mass loss and a 33.11% increase in decomposition onset temperature compared to the control, indicating enhanced thermal stability. Furthermore, using foundry sand mixed with metal chips yielded improvements in green compressive strength of 20.33%, dry compressive strength of 22.73%, and compactability of 4.55%. Overall, this study confirms that integrating metal chips into sand molds significantly enhances both the fatigue strength of aluminium alloy castings and the quality of the molds, presenting promising implications for the recycling and utilization of scrap materials in casting processes.