Thermodynamic analysis of aluminium-based sacrificial anode alloys phase composition

Abstract

Literature review on magnesium, zinc and aluminum-based sacrificial anode alloys chemical and phase compositions have been performed. Technological phase diagrams of aluminum-based sacrificial anode alloys with different content of harmful additives, such as iron, silicon and copper, have been calculated and constructed. It is determined that the harmful effect of iron is in faster dissolution of the anode due to large inclusions of iron intermetallic. This iron negative effect can be eliminated in several ways: a) maximization of the melt cooling rate, which will lead to significant grinding of the intermetallics and thus reduce their negative impact; b) high-temperature homogenization of the alloy with subsequent rapid cooling, which will reduce the size of the iron intermetallic inclusions; c) doping the alloy with additional manganese to bind iron in ternary compound, which has a different shape and size than the binary intermetallic and has less negative effect on the sacrificial anode alloy.
To eliminate the negative effects of silicon, the alloy has to be additionally doped with magnesium in an amount that will ensure the silicon complete binding. In this case, the phase composition of the alloy will correspond the AP4 alloy (% wt.%: (4.0-6.0) Zn), (0.5-1.0) Mg, (0.05-1.00) Sn , ˂ 0.10 Si, ˂ 0.10 Fe, ˂ 0.01 Cu).
Long-term heat treatment of the alloy at a temperature of 120 ° C is proposed to reduce the copper harmful effect on the aluminum-based sacrificial anode alloys. Almost all copper can pass from the solid aluminum solution into the Al₂Cu compound during this processing.