Formation of Phases and Microstructures in Al-8Si Alloys with Different Mg Content

Abstract

Mg-containing high-silicon aluminum alloy is a heat-treatable aluminum alloy that is now widely used in the aerospace and automotive industries because of its high specific strength, high wear resistance and corrosion resistance, low thermal expansion coefficient, and low cost. More attention has been paid to optimizing the microstructure to increase the performance of this type of aluminum alloy. In the present work, the solidification processes of Mg-free and Mg-containing (0.33–1.32%) Al-8Si alloys were analyzed by the experimental results combined with the thermodynamic calculation. The results showed that α-Al, Si, and Al5FeSi were in the Mg-free Al-8Si alloy ingots, while the Al5FeSi phases in alloys with Mg additions were transformed into π phases (Al8Mg3FeSi6) by the reaction L+Al5FeSi→α-Al+Si+Al8Mg3FeSi6. There was a binary eutectic reaction of L→α-Al+Al5FeSi when the Mg content exceeded 0.51% and the Fe content was higher than 0.17%. With the increase of Mg content, the volume of Mg2Si was gradually increased while the divorced eutectic phenomenon of the quaternary eutectic structure (α-Al+Si+Mg2Si+Al8Mg3FeSi6) was weakened and the eutectic structure was significantly refined.

Clustering and Precipitation during Early-Stage Artificial Aging of Al–Si–Mg(–Cu) Foundry Alloys

“…For instance, the solubility of Mg in Al containing 10 at.% Si is about 0.45 at.% Mg at 525 • C [57,58]. In Figure 3, we see that this results in a significant amount of π-Al8Mg3FeSi6 phase [59] inside alloy Mg0.60. The resulting loss of Mg from the Al grains explains the peak hardness of Mg0.60 not being higher than that of Mg0.45.…”

Calculation Based on the Formation of Mg2Si and Its Effect on the Microstructure and Properties of Al–Si Alloys

“…The addition of Mg mainly affects the formation of Mg 2 Si and the distribution of solute elements in the matrix. Ni Tian et al [12] found that the volume of Mg 2 Si was gradually increased, while the divorced eutectic phenomenon of the quaternary eutectic structure was weakened with the increase in Mg content. After T6 treatment, the fine dispersed β(Mg 2 Si) phase and the Q(Al 5 Cu 2 Mg 8 Si 6 ) phase precipitated successively, which played a dispersion strengthening role in the alloy.…”