Effects of eutectic modifier and high-pressure torsion processing on microstructure and corrosion resistance of hypoeutectic Al-7Si alloy

Abstract

High-pressure torsion (HPT) has recently been proven as an effective technique to produce bulk ultrafine-grained materials. Both strontium-modified and unmodified Al-7Si alloys were processed by HPT under an applied pressure of 6.0 GPa for different numbers of torsional revolutions and then exposed to a 3.5 wt.% NaCl solution for open-circuit potential measurements followed by electrochemical impedance spectroscopy and potentiodynamic polarization curve tests. The results exhibit that corrosion resistance of both Al-7Si and Al-7Si-Sr alloys in NaCl solution is enhanced upon high torsion strains of HPT processing compared with that of the as-received sample, but the improvement in corrosion resistance for Al-7Si alloy is more significantly than the Sr-modified alloy, which is possibly due to the increased HPT-induced active sites, the homogenous microstructure and the breakage of brittle coarse silicon particles and intermetallic phases demonstrated by microstructure and microhardness measurements. The corroded samples were further characterized with scanning electron microscopy and energy dispersive X-ray spectroscopy to examine the effect of grain refinement on corrosion mechanism of the Al-7Si alloy.

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Identifiers

ORCID for Mengyan Nie: orcid.org/0000-0002-7758-760X

ORCID for N. Gao: orcid.org/0000-0002-7430-0319

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