Corrosion resistance of Electron 21 magnesium alloy

Purpose: Elektron 21 magnesium alloy containing neodymium, gadolinium and zinc has high strength, good corrosion resistance and excellent castability. It is designed mainly for aerospace applications. The purpose of the investigation was to study the corrosion resistance of Elektron 21 magnesium alloy in as cast condition and after heat treatment in 3.5% NaCl saturated with Mg(OH)2 solution. Design/methodology/approach: Solution treatment was performed at 525 degrees centigrade/8h/water, while ageing treatments at following conditions 250 degrees centigrade/4-96h/air. Immersion test was performed in 3.5% NaCl saturated with Mg(OH)2 solution at room temperature. Specimens were placed in 3.5% NaCl solution for periods of time between one and 5 days. After immersion test, the microstructure and the appearances of the corroded structure were examind by optical microscopy (Olympus GX-70) and a scanning electron microscopy (Hitachi S3400). Findings: The corrosion rates of Elektron 21 alloy increased with increasing the exposure time and finally (after 5 days) reached maximum value 0.092 mg/cm to the -2 day to the -1. Solution treatment at 520 degrees centigrade for 8 h caused decrease in corrosion rate (0.072 mg cm to the -2 day to the -1) due to dissolving of intermetallic phase precipitates at matrix. Ageing at 200 degrees centigrade for 4 h and 16 h caused next decrease in corrosion rate to value 0.052 and 0.055 mg cm to the -2 day to the -1 respectively, while after ageing for 48h corrosion rate increase to value 0.067 mg cm to the -2 day to the -1 due to increase of volume fraction and size of beta' phase and precipitations of equilibrium beta phase. It was also noticed that the longer time of ageing the higher corrosion rates were observed. Research limitations/implications: Future researches should include investigations of the influence of other environments on the corrosion resistance of Elektron 21 alloy. Practical implications: The improvement of corrosion resistance of Elektron 21 alloy can cause increase in it application in aerospace industry. Originality/value: The relationship between the ageing parameters, microstructure and corrosion resistance in Electron 21 magnesium alloy was specified.