Chemical modification of morphology of Mg₂Si phase in hypereutectic aluminium–silicon–magnesium alloys

Abstract

Hypereutectic Al-Si alloys that contain more than 3 wt-%Mg exhibit a microstructure that consists of eutectic Si and Mg 2 Si in a-Al matrix that is devoid of primary silicon particles. The Mg 2 Si phase is desirable in the Al-Si microstructure because of its high melting temperature, low density, high hardness, low coefficient of thermal expansion and high elastic modulus. However, at such relatively high concentrations of Mg, the Mg 2 Si phase tends to be in a morphology that detracts from the alloys' mechanical properties. Several chemical modifiers were added to the alloy in order to refine the morphology of the Mg 2 Si phase. A combination of strontium and misch metal was found to yield the best results in that the microstructure obtained after a standard T6 heat treatment exhibits almost spherical Mg 2 Si particles. Tensile test bars cast from the modified alloy in steel moulds have very good room temperature tensile properties and good hardness.

An Investigation into the Potential of Turning Induced Deformation Technique for Developing Porous Magnesium and Mg-SiO2 Nanocomposite

“…Spotted regions were observed in both TID Mg-2SiO 2 materials as well as furnace-sintered Mg. For furnace-sintered Mg, these spotted regions were of thin, linear, amorphous structures while for Mg-SiO 2 , these regions resemble dendritic and lamellar structures containing Mg 2 Si much like those obtained by cast Al-Mg-Si alloys in other works [ 40 , 41 ]. The presence of Mg 2 Si is further confirmed by EDX results indicating the distributed presence of Si and O in addition to Mg across an area of Mg-2SiO 2 turnings rather than just on a singular point as well as XRD results in Section 3.4 .…”

Structure and mechanical behavior ofin situdeveloped Mg2Si phase in magnesium and aluminum alloys – a review

“…The b 00 particles are rapidly dissolved during high-temperature heating or aging and Si and other precipitates are formed. 36 Mandal et al 37 reported that hypereutectic Al-Si-Mg alloys with more than 2 wt% Mg exhibit a microstructure in which the Si particles are inherently rened and uniformly distributed. On further increasing the Mg content, both the amount and size of the Mg 2 Si phase increase.…”