The Influence of Stress and Annealing Conditions on the Corrosion Behavior of Pure Magnesium

A stent is a medical device that acts as a scaffold to internally support weak or narrowed blood vessels. Conventional stents are generally manufactured from biocompatible grades of stainless steel and remain semi-permanently in the body with the possible risks of restenosis and throm-bosis. Magnesium, which has excellent biocompatibility and biodegradability, has recently been attracting attention as a candidate material for bioabsorbable stents that gradually disappear over time. A significant challenge to the application of magnesium to stent technology is the dif-ficulty in controlling its corrosion rate in-vivo. Following implantation in a blood vessel the stent will be repeatedly subjected to tensile and compressive stresses due to the pulsatile blood flow induced by the beating of the heart. This paper investigates the effects of stress and heat treatment on the corrosion behaviour of pure magnesium. Corrosion testing and grain-size measurements were conducted on pure mag-nesium samples which were subjected to tensile strain, compressive strain and repeated tensile-compressive cyclic stress following heat treatment processing. It was observed that mass loss of specimens with refined crystal grains was decreased by the application of strain or cyclic stresses and annealing near the recrystallization temperature region. Conversely, heat treatment in the high-temperature region increased mass loss in specimens with coarsened grains. It is thus sug-gested that grain refinement improves corrosion resistance while grain coarsening decreases re-sistance.