Influences of Al–20Si–2.5Fe–2Mn Master Alloy Additions on the Microstructure and Mechanical Properties of Hypereutectic Al–20Si Alloys

Abstract

A novel Al–20Si–2.5Fe–2Mn master alloy containing α-Al15(Fe, Mn)3Si2 particles was developed to modify Si phases of hypereutectic Al–20Si alloy. The microstructure of as-cast specimens was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with energy-dispersive spectrometers (EDS), electron probe micro-analysis (EPMA), and X-ray diffraction (XRD). The morphology of primary Si phases changed from coarse irregular pentagonal and polygonal shapes to fine blocky shapes as the adding content of the master alloy increased up to 6.0%. The mean size of the primary Si phases decreased by 70.3% from 118 to 35 μm. Moreover, the shape of eutectic Si structure changed from coarse flakes or acicular shape to fine fibrous structure and granular particles. Furthermore, the Si phases were refined and homogenized when 6.0% master alloy was added into Al–20Si alloy. The optimum elongation (El) increased by 45.8% from 0.85 to 1.24%, and the optimum ultimate tensile strength (UTS) increased by 34.6% from 130 to 175 MPa comparing with unmodified Al–20Si alloy. In addition, the refinement and modification mechanisms of Si phases are also discussed on the hypereutectic Al–20Si alloys with the addition of master alloy.