Simultaneous refinement of α-Al and modification of Si in Al–Si alloy achieved via the addition of Y and Zr

Abstract

Due to the Si/Zr-poisoning effect, conventional refiners often yield unsatisfactory results in refining α-Al grains for Al–Si alloys. In this work, the refinement of α-Al grains and the modification of eutectic Si are simultaneously achieved through the combined addition of Y and Zr to A356 alloy. The results indicate that the individual addition of Zr aids in refinement due to the formation of heterogeneous nuclei Al3Zr, while Y alone can refine α-Al grains and modify eutectic Si to a certain extent. When Y and Zr are added together, not only is the size of α-Al grains further refined to 22.1 μm, but the morphology of eutectic Si is also completely transformed into a fibrous structure. The interaction between Zr and Y decreases their solubility in the matrix, enhances heterogeneous nucleation, and induces the formation of a Al8FeMg3Si6YxZry phase enriched at grain boundaries, suppressing the growth of eutectic Si flakes. Compared to the use of Al–Ti–B refiners and Sr modifiers, the alloy with 0.25Zr and 0.3Y additions exhibits more significant grain refinement and Si modification. Furthermore, it facilitates the precipitation of fine Al3(Y, Zr) particles during the T6 heat treatment process, resulting in an optimal ultimate tensile strength (UST) of 289 MPa and an elongation of 9.75%.