Introduction and Objectives: Due to the negative impact of increasing Mg content on the ductility and toughness of Zn-Mg alloys, the use of dilute forms of these alloys has recently become more widespread. In this study, the effect of chill modification and friction stir processing (FSP) on the microstructure and corrosion behavior of dilute Zn-0.3Mg alloy were studied.
Materials and Methods: The FSP was performed using a simple cylindrical tool under rotation speed of 1600 rpm and travel speed of 12 mm/min on solidified alloy at a cooling rate of 4.1 °C/s. To investigate the effect of chill modification, the solidification rate was increased from 4.1 to 14.7 °C/s. Tafel polarization and electrochemical impedance spectroscopy (EIS) experiments were performed in simulated body fluid (SBF).
Results: The Tafel polarization test results indicated that the corrosion current densities of the chill-modified alloy (20.9 μA/cm²) and friction stir processed alloy (19.6 μA/cm²) are lower than that of the as-cast alloy (38.8 μA/cm²) by about 46 and 49%, respectively. The EIS also implied increasing corrosion resistance of the as-cast alloy from about 50 Ω to 85 Ω and 1.5 kΩ in the chill modified and friction stir processed samples, respectively.
Conclusion: Due to the ultrafine and homogenous distribution of Mg₂Zn₁₁ particles and development of ultrafine grains (increasing the grain boundary density), the surface of the processed samples (especially the friction stir processed ones) are covered by a continuous and compacted layer composed of corrosion products causing improved corrosion resistance of Zn-0.3Mg alloy.