Investigation of castability, mechanical, corrosion properties and flammability of ML-OPB and EWZ43 magnesium alloys

Abstract

Magnesium alloys are usually considered as structural materials when the weight reduction is important - in aircraft and space industry for example. In recent years, there has been an increase in the use of new generation ignition-proof high-strength magnesium alloys in the design of aircraft parts. The properties of new ignition-proof casting magnesium alloys ML-OPB (Mg–6.7Y–2.6Zn–0.5Zr–0.35Ce– 0.35Yb; wt.%) and EWZ43 (Mg–3.8Y–4.4Nd–0.6Zr–0.6Zn; wt.%) were investigated and compared with properties of commercial magnesium alloys. The microstructure of investigated alloys in the as-cast condition comprises of a magnesium solid solution and a significant amount of eutectic. Heat treatment according to the T6 mode results in change in the eutectic phase’s morphology and also to their partial dissolution in the magnesium matrix. Long-term high-temperature holding, simulating operating conditions (500 h at 300 °C), leads to the formation of precipitates along the grain boundaries in both alloys, significantly reducing the mechanical properties. During the oxidation of the samples, it was established that the main components that involved into the oxide film and provides the protective properties of the alloys is Y, Nd and Yb. The investigated alloys have a high strength, which is not lower than that of the ML10 alloy. At the same time, the advantage of the ML-OPB alloy is a high elongation at fracture, while the EWZ43 alloy is characterized by high strength. The corrosion rate of the investigated alloys exceeds the corrosion rate of known commercial ML10 and AZ91 alloys, which implies the need for additional protection against corrosion of investigated alloys. At the same time, the castability of ML-OPB and EWZ43 alloys is no lower than that of most commercial magnesium alloys. An oxide film with high Y content and high protective properties is formed when the alloys interact with the sand mold bonded with furan resin. The ignition temperature of the investigated alloys is 100–150 °C higher than that of the ML10 alloy. The flammability test of alloys in the flame of a gas burner, made on cone samples and typical aircraft castings «bracket», showed that ML-OPB and EWZ43 alloys are almost non-flammable under the conditions of experiment.