Effect of solution treatment on corrosion characteristics of biodegradable Mg-6Zn alloy

A binary Mg-6Zn biodegradable alloy was solution treated to evaluate the effects of resulting microstructure changes on the alloy's degradation rate and mechanisms in-vitro. The treatment was conducted at 350 °C for 6-48 h. Optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were used to analyze the as-cast and treated samples. Immersion and electrochemical tests were performed in simulated body fluid at 37 °C to assess the samples corrosion resistance. To confirm the results of the corrosion tests, pH measurement was carried out. It is found that over 24 h solution treatment dissolves intermetallic phases in matrix and produces an almost single phase microstructure. Decreasing the intermetallic phases results in lower cathode/anode region ratios and lowers corrosion rates. The results of the electrochemical and mass loss tests reveal that extended solution treatment improves the corrosion resistance of the alloy. The results also show that solution at 350 °C for 24 h enhances the corrosion resistance of the as-cast alloy more than 60%. In addition, decreasing intermetallic phases in the microstructure accompanied a lower pH rise reduced corrosion rate. Solution treatment is suggested as a corrosion improving process for the application of Mg-Zn alloys as biodegradable implant materials.