Influence of Al and Mn additions on the microstructure and corrosion properties of extruded Mg–8Sn–1Zn alloys

Abstract

The microstructure and corrosion properties of extruded Mg–8Sn–1Zn alloys with varying Al contents were investigated. The microstructures of the extruded alloys mainly consisted of α-Mg grains and Mg2Sn particles in common. The addition of Al to the ternary alloy resulted in the formation of different types of Al–Fe-based intermetallic particles depending on Al contents. Corrosion rates were found to be drastically increased by additions of 1 – 3wt% Al. The extruded alloys with 1 – 3wt% Al showed over 30 times higher corrosion rates than those containing less than 0.3wt% Al in 0.6 M NaCl solution. The increase in corrosion rate produced by the Al addition was attributed to the presence of Al5Fe2 particles, which act as strong cathodic sites for H2 evolution during corrosion. In addition, a solution to reduce the high corrosion rate of the Mg–8Sn–1Zn alloys containing Al is suggested. The presence of Al5Fe2 particles, having deleterious effect on corrosion resistance, can be replaced by that of Al8Mn5 particles by the addition of Mn to the Mg–8Sn–1Zn alloys with 1 – 3wt% Al. The Mg–8Sn–1Zn–1Al alloy with 0.1wt%Mn showed over an order lower corrosion rate than the quaternary alloy without Mn, which can be attributed to the relatively sluggish cathodic reaction in the presence of Al8Mn5 particles.