Effect of Rare Earth Dy (dysprosium) on the Microstructures and Mechanical Properties of Hypereutectic Al–Si Alloy

In the present work, the effects of Dy (dysprosium) additions (0, 0.05, 0.1, 0.15, 0.2, and 0.3wt%) on the microstructure and mechanical properties of hypereutectic Al–Si alloy have been studied. An inductively coupled plasma optical emission spectrometry (ICP-OES) apparatus was employed to measure the alloy composition. The specimens were examined using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS). In the as-cast state, increasing the Dy content to 0.15% resulted in the refinement of the primary Si morphology from irregular polyhedral and branched shapes to fine polyhedral shapes, with the average size decreasing by 21% from 48 to 38 μm. Additionally, the eutectic Si transformed from coarse, uneven short rod-like structures to fibrous ones. Moreover, the tensile strength increased to 233 MPa, marking an 18.8% improvement, while the elongation reached 1.1%, indicating a significant increase of 267%. After T6 heat treatment, with a Dy content of 0.2%, the size of primary Si and eutectic Si did not change significantly compared with the 0.15% Dy addition. However, the mechanical properties of the alloy were optimized at this Dy content due to the fragmentation of the Al–Si-Fe-Mn phase and Al2Cu phase. The tensile strength increased to 242 MPa, reflecting a 14.7% improvement, and the elongation improved to 1.28%, representing a 60% enhancement compared with the alloy without Dy addition.

Graphical Abstract