Property Comparison of Rheocasting and Die Casting Components

Thixotropic alloys provide excellent casting properties, enabling both thin- and thick-walled parts. Compared to conventional die casting, the process allows for the use of lower-Si alloys, opening new applications such as high-thermal-conductivity heat sinks. Rheocasting offers the use of mixed scrap to produce tailored alloy compositions. This study investigates components produced using the Rheometal® process. Three alloy types were examined: a conventional die-casting alloy (EN-AC 42100), the wrought alloy EN-AW 6082, and a mixed scrap alloy (AlSi4MnMg) of the two alloys. Porosity via microtomography was analyzed in thick-walled automotive components, while mechanical properties were evaluated via bending tests in thin-walled sections. The smallest porosity of 1.05 (in D185 core) and 1.40 (in 1.2343 core) was observed. At moderate piston speeds (1.5 m/s), the mechanical properties of AlSi4MnMg are in the same range as those of HPDC (~5500 N at 5 mm displacement for both samples). All materials show globular primary α particles observed by optical microscopy with diameters of 10 to 50 µm, independent of the core type used. Corrosion behavior was studied in 3.5 wt.% NaCl solution using electrochemical techniques, including open circuit potential, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy. The best electrochemical performance was observed for the mixed scrap alloy with the lowest corrosion density of ~0.26 µA/cm² and annual corrosion rate of ~0.11 mpy, along with the highest repassivation potential of -700 mV. Scanning electron microscopy-energy dispersive analyses revealed the formation of the CrMn-rich oxide layer after PDP for all samples, where needle-like MgSi₂ and α-Al(Fe,Mn)Si phases are the distinctive features of EN-AC 42100 and mixed scrap alloy, respectively. The results highlight the potential of rheocasting for circular aluminum production, offering for the first time the opportunity to utilize combined as-cast and as-wrought scrap streams to tailor alloys with attractive casting, mechanical, and corrosion-performance characteristics.