Comparative Study on Corrosion Behavior of WE33 in Immersion and Polarization Influenced by Heat Treatment

An extruded WE33 alloy is focus of this study. The influence of heat treatment on hardness and corrosion behavior is evaluated in immersion and polarization tests. Due to the application as a biodegradable implant, Ringer solution of 37 °C was chosen. As-extruded WE33 shows heterogeneous grain size distribution. Solution heat treatment (T4) causes significant grain growth with high variation in grain size with reduced hardness. Precipitation hardening (T6) causes reduced average grain size, mainly based on developing additional small grains. Hardness of T6 condition exceeds extruded material. The corrosion morphology is mostly described by the pitting factor. Corrosion behavior by corrosion rate (weight and cross-sectional area loss) and pitting factor of immersion are compared to polarization and shows the same trend: T6-condition shows lowest corrosion rate. On the other hand, T6-condition shows highest pitting corrosion tendency. Pitting factors evaluated in immersion tests are much higher than seen after polarization tests.