Microstructure and mechanical properties of Elektron 21 alloy after heat treatment

Purpose: Elektron 21 is new magnesium based casting alloy contains neodymium, gadolinium and zinc for used to at 200 degrees centigrade. It is a Mg-RE-Zn-Zr alloy designed for aerospace and specialty application ns. This alloy has high strength, good corrosion resistance and excellent castability. The aim of the research was to determine the effect of heat treatment parameters on the microstructure and mechanical properties of Electron 21 magnesium alloy. Design/methodology/approach: Solution treatment was performed at 520 degrees centigrade/8h with water cooling. Ageing treatments were performed at 200 degrees centigrade/4-96h and then quenched in air. The microstructure was characterized by JEM 2010 ARP microscope. The examination of the mechanical properties was conducted on an MTS-810 servo hydraulic machine at two temperatures: ambient (ca. 20 degrees centigrade) and 200 degrees centigrade. Hardness measurements by Vickers method were performed on a ZWICK/ZHV50 hardness tester. Findings: The microstructure of the cast alloy consists of alpha-Mg phase matrix with precipitates of intermetallic phase Mg12(Ndx, Gd1-x) at grain boundaries. After solution treatment the Mg12(Ndx, Gd1-x) phase dissolves in the matrix. The ageing treatment applied after solution treatment with air-cooling caused precipitation of a beta'', beta' and beta intermetallic phases. The best mechanical properties (Rm=308MPA, R0.2=170MPa, A5-9.5%) has a alloy with beta' intermetallic phase. Research limitations/implications: The future research will contain microstructural investigations of Elektron 21 alloy after creep tests. Practical implications: Elektron 21 magnesium alloy is used in the aircraft industry for engine casings, gear box casings and rotor heads in helicopters. Results of investigation may be useful for preparing heat treatment technology of the Mg-Nd-Gd alloys. Originality/value: The results of the researches make up a basis for the next investigations of magnesium alloys with addition of Gd and Nd designed to exploitation at temperature to 300 degrees centigrade.