Prediction of corrosion resistance of Magnalias

Abstract

In the presented work the factors influencing the strength and corrosion rate in seawater of magnalium aluminum-magnesium alloy were considered. It was shown that in unsaturated solid alpha solutions the main form of magnesium in the aluminium structure was the electronic compound Mg2Al4 entering the rhombic subsystem of aluminium cells. The calculation showed that the more aluminium cells contain Mg2Al4 group as a rhombic subsystem, the higher the strength of these alloys. The mechanism of destruction by halogen ions of pure aluminium cells and aluminium cells containing the Mg2Al4 group was determined by the PM3 method. Destruction of both types of cells occurred by the same scenario, through the detachment by halogen ions of the central atom in the upper edge of cells bordering. It was shown that in seawater the corrosion rate of aluminium cells containing Mg2Al4 group was higher than the corrosion rate of pure aluminium cells. A mathematical model has been developed that allows calculating the change in the corrosion rate of magnesium alloys with low magnesium mass fraction (up to 3.5 % magnesium inclusive) in seawater. The model allowed to take into account the change of influence of the mass fraction of the main alloying elements (Mg, Cr, Mn, Zn, Ti, Cu) on the corrosion rate. Change of corrosion rate in seawater of three aluminium-magnesium alloys variants was calculated using this model. These aluminium alloy variants include a magnesium content of 2.6 mass % with higher levels of the alloying elements Cr and Mn.