Corrosion of an extruded magnesium alloy ZK60 component—The role of microstructural features

The microstructure and corrosion behavior of an extruded magnesium alloy ZK60 bumper were investigated using optical microscopy, SEM and EDS as well as potentiodynamic polarization technique. The results show that the microstructure of the component is characterized by two distinct layers: the skin with coarse grains and the interior with fine grains. Preferential attack on the interior is attributed to the macrogalvanic corrosion between the two layers with an initial potential difference. The size and distribution of the intermetallic compounds play a crucial role in pitting corrosion and intergranular corrosion.

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► Microstructure of an extruded ZK60 bumper on the cross-section is characterized by two distinct layers.
► The microstructures on the extrusion direction are characterized by equiaxial grains and MgZn intermetallic compounds.
► Preferential attack occurred on the interior rather than the skin.
► The corrosion morphology is correlated to grain size and to the size and distribution of the intermetallic compounds.