The Investigation Of The Corrosion Fatigue Properties Of The Degradable Magnesium Alloy

As a promising biodegradable material,magnesium alloys have received widespread attention and played an important role in orthopedic implants.In the human body,magnesium alloys are subject to both the corrosive effects of the biological environment and the multiaxial cyclic loads imposed by human motion.The interactions of corrosion and cyclic loading can cause corrosion fatigue failure of magnesium alloy implants during service.It can destroy the surrounding tissues and,in serious cases,it can also endanger life.Therefore,the study of corrosion fatigue performance of magnesium alloy is very valuable for its practical clinical application.In the first part,2% and 4% pre-compressive strains were applied to the original AM60 extruded bar.The impacts of pre-compressive deformation on uniaxial corrosion fatigue of AM60 magnesium alloy were analyzed by electrochemical experiment,hydrogen evolution experiment and corrosion fatigue experiment.The results show that the twins introduced by pre-compression will accelerate the corrosion rate of magnesium alloy to a certain extent,and significantly reduce the local corrosion phenomenon.With the increase of pre-compression deformation,the distribution of twins in the magnesium alloy matrix is more compact and uniform,and sufficient pre-compression deformation can significantly reduce the pitting corrosion of the magnesium alloy.In the corrosion fatigue experiment under high cyclic stress amplitude,the twinning and de-twinning process caused by pre-twins accelerates the mechanical damage of the material and reduces its corrosion fatigue performance.Under the low cyclic stress amplitude,sufficient pre-compression deformation can significantly reduce corrosion pits and strip corrosion marks,thereby significantly improving the material's corrosion fatigue performance.In the second part,four different paths of cyclic stress were applied to thin-wall specimens in a corrosive environment to investigate the corrosion fatigue behavior of magnesium alloys under different loading paths.The results show that circular path loading can significantly accelerate the mechanical damage of the material and make its corrosion fatigue performance significantly lower than the other three loading paths.For the other three loading paths,the mechanical damage difference determines the corrosion fatigue performance of the materials at the higher equivalent stress amplitude,which makes the longest life of the uniaxial tension-compression path,followed by the proportional loading path,and the life of cyclic torsion path is the shortest.Under the lower equivalent stress amplitude,local corrosion phenomena such as strip corrosion and pitting corrosion are the key locations for inducing crack initiation.The strip corrosion provides favorable conditions for multiaxial corrosion fatigue crack propagation perpendicular to the strip.The magnitude of the principal stress significantly affects the corrosion fatigue life under multiaxial loading paths.This makes the uniaxial tension-compression path and proportional loading path life basically the same,and the life of the cyclic torsion path is significantly increased.