The effect of different heat treatments on the microstructure and corrosion resistance of ZK60 magnesium alloy

This study investigates the effects of T5, T6, and DT6 treatments on the microstructure and corrosion resistance of as-extruded ZK60 magnesium alloy. The results indicate that the corrosion resistance of the alloys follows a decreasing trend: T5 treated > DT6 treated > as-extruded > T6 treated. The corrosion rate of the alloy is determined by the interaction mechanism of precipitates, geometrically necessary dislocations (GNDs), grain geometric characteristics and orientation parameters. The morphology and distribution characteristics of the β′ phase are the primary factors influencing corrosion resistance. After extrusion, short β′ 1 phases and fine β′ 2 phases are formed. After T5 treatment, the increase in GNDs and the promotion of the dispersed precipitation of appropriate β′ 1 and β′ 2 phases hinder dislocation movement across grain boundaries and increase grain roundness, resulting in optimal corrosion resistance. T6 treatment promotes the extensive nucleation of rod-like β′ 1 phases and obstructs the recrystallization process. This leads to the overlap of dislocation slip planes with corrosion paths, accelerating the propagation rate of corrosion cracks. After DT6 treatment, the formation of β′ 1 phases is suppressed, and β′ 2 phase nucleation is promoted. The extensive precipitation of β′ 2 phases inhibits the activation of slip systems in grains with high Schmid factors (SF). Appropriate texture strength under specific orientations improves corrosion resistance.