In this study, the relationship between the extrusion ratio and the corrosion resistance
of pure Mg deformed using extrusion with an oscillating die (KoBo) without preheating
of the initial billet was investigated. The materials investigated in this study were
extruded at high deformation ratios, R1 5:1, R2 7:1, and R3 10:1, resulting in significant
grain refinement from the very coarse grains formed in the initial billet to a few
µm in the KoBo-extruded samples at room temperature, which is not typical for hexagonal
structures. Our research clearly shows that KoBo extrusion improves the corrosion
performance of pure Mg, but there is no straightforward dependence between the extrusion
ratios and corrosion resistance improvement. Although it was expected that the smallest
grain size should provide the highest corrosion resistance, the dislocation density
accumulated in the grain interiors during deformation at the highest extrusion ratio,
R3 10:1, supports dissolution reactions. This, in turn, provides the answers for the
greater grain size observed after deformation at R2 7:1, where dynamic recovery prevailed
over dynamic recrystallization. This situation led to the annihilation of dislocation,
leading to better corrosion resistance of the respective alloy. Therefore, the alloy
with the greatest grain size has the best corrosion resistance.
