Fatigue and Corrosion Fatigue Properties of Mg–Zn–Zr–Nd Alloys in Glucose-Containing Simulated Body Fluids

Abstract

Medical bone implant magnesium (Mg) alloys are subjected to both corrosive environments and complex loads in the human body. The increasing number of hyperglycemic and diabetic patients in recent years has brought new challenges to the fatigue performance of Mg alloys. Therefore, it is significant to study the corrosion fatigue (CF) behavior of medical Mg alloys in glucose-containing simulated body fluids for their clinical applications. Herein, the corrosion and fatigue properties of extruded Mg-Zn-Zr-Nd alloy in Hank’s balanced salt solution (HBSS) containing different concentrations (1 g/L and 3 g/L) of glucose were investigated. The average grain size of the alloy is about 5 μm, which provides excellent overall mechanical properties. The conditional fatigue strength of the alloy was 127 MPa in air and 88 MPa and 70 MPa in HBSS containing 1 g/L glucose and 3 g/L glucose, respectively. Fatigue crack initiation points for alloys in air are oxide inclusions and in solution are corrosion pits. The corrosion rate of the alloy is high at the beginning, and decreases as the surface corrosion product layer thickens with the increase of immersion time. The corrosion products of the alloy are mainly Mg(OH)₂, MgO and a small amount of Ca-P compounds. The electrochemical results indicated that the corrosion rate of the alloys gradually decreased with increasing immersion time, but the corrosion tendency of the alloy was greater in HBSS containing 3 g/L glucose. On the one hand, glucose accelerates the corrosion process by adsorbing large amounts of aggressive Cl⁻ ions. On the other hand, glucose will be oxidized to form gluconic acid, and then reacts with Mg(OH)₂ and MgO to form Mg gluconate, which destroys the corrosion product film and leads to the aggravation of corrosion and the accumulation of fatigue damage.