Microstructure characteristics and mechanical properties improvement of gravity cast Al-7Si-0.4Mg alloys with Zr additions

Al-7Si-0.4Mg alloys are one of the most commonly applied aluminum alloys in various casting processes. In this study, 0.06%, 0.14% and 0.20% Zr are added to gravity cast Al-7Si-0.4Mg alloys. The microstructural analysis of the as-cast alloys with Zr shows the formation of (Al,Si)(3)(Zr,Ti) and pi-Fe phases. Compared with alloys without Zr, the alloys with Zr have finer grains; additionally, a small secondary dendrite arm spacing (SDAS) is obtained with a proper Zr content. After T6 heat treatment, the Mg in Fe-rich intermetallics diffuse into the matrix, decreasing the size of the intermetallic phases. Nanoscale precipitates of the (Al,Si)(3)(Zr,Ti) phase are found in alpha-Al grains. Due to the finer grains and smaller SDAS as well as the presence of (Al,Si)(3)(Zr,Ti) precipitates, the tensile strength and elongation of the alloys with 0.06% Zr are 332 MPa and 8.7%, respectively, whereas those of the Al-7Si-0.4Mg alloys without Zr are 302 MPa and 4.6%, respectively.

Automated summary

Adding different Zr contents to Al-7Si-0.4Mg alloys can lead to the formation of finer grains and proper SDAS. After T6 heat treatment, Mg diffuses into the matrix, reducing the size of intermetallic phases, and nanoscale precipitates are found in alpha-Al grains.