Abstract

HERNANDEZ HERNANDEZ, Luis Salvador et al. Coverings of chemical conversion over powder-metallurgical magnesium and alloy AZ31 as possible biodegradable implants. Rev. Met. UTO [online]. 2016, n.38, pp. 5-15. ISSN 2078-5593.

In order to improve the corrosion resistance of magnesium and a magnesium alloy in applications as biodegradable implant materials, phytic acid (pa) or hydrofluoric acid (HF) conversion coatings were formed on pure magnesium and AZ31 magnesium alloy by immersion treatment at 60 °C or room temperature, respectively. Pure magnesium was prepared by powder metallurgy. The scanning electron microscopy images revealed an uniform coating with some pores on the specimens immersed in HF, while a compact although cracked coating was observed on the specimens immersed in pa. In the first case, X-ray diffraction analysis indicated that the coating was mainly composed of MgF₂. In the second, infrared spectroscopy showed that the main coating components were the chelate compounds formed between pa and the metallic ions. The corrosion resistance of untreated and coated samples was evaluated by potentiodynamic polarization and electrochemical impedance techniques in phosphate buffered saline at 37 °C. The results indicated that both conversion coatings initially provided a very effective protection to the magnesium substrates. However, the protection ability decreased sharply as time elapsed

Keywords : Conversion coatings; AZ31 alloy; powder metallurgy magnesium; corrosion resistance.