Effect of heat treatment on corrosion behavior of low pressure sand cast Mg-10Gd-3Y-0.5Zr alloys

Abstract

M agnesium alloys containing heavy rare earth elements are of high strength and low density, which makes them very attractive as structural materials in applications, for example, aircraft and space machinery, and ground transport including racing automobiles, where weight saving is of great importance [1][2][3] . It has been reported that the recently developed Mg-Gd-Y-Zr alloys such as Mg-10Gd-3Y-0.5Zr alloy show considerable precipitation hardening, leading to improved specific strength at both room and elevated temperatures, and better creep resistance than conventional Al and Mg alloys [4][5][6] . According to the literature [7,8] , Mg-10Gd-3Y-0.5Zr alloy is employed to produce complicated Abstract:The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr (wt.%) alloys in as-cast, solution treated (T4) and aged (T6) conditions were studied by means of immersion test and electrochemical measurements in 5wt.% NaCl solution saturated with Mg(OH) 2 . It was observed that the corrosion rate in the T4 condition was lower than that of the as-cast and T6 conditions by both sand casting and permanent mold casting with the same order of as-cast>T6>T4; while the corrosion resistance of the permanent mold casting is superior to the sand casting. The morphologies of the corrosion products are similar porous structures consisting of tiny erect flakes perpendicular to the corroded surface of the alloy, irrespective of the heat treatment conditions. Especially, the corrosion film in T4 condition is more compact than that in the other two conditions. In addition, the severer corrosion happening to the as-cast condition is correlated with the galvanic corrosion between the matrix and the eutectic compounds; while improved corrosion resistance for the T4 and T6 conditions is ascribed to the dissolution of the secondary eutectic compounds. The measured corrosion current densities of Mg-10Gd-3Y-0.5Zr alloys in as-cast, T4, and T6 conditions are 36 μA·cm components by low-pressure sand casting (LPSC) in production for the combination of higher strength and higher ductility than other Mg-Gd-Y alloys. Moreover, LPSC is an appropriate technique to produce Mg components, especially those with thin-walls (2-5 mm) and complex geometry [9] . In the past few years, many investigations related to the microstructure, mechanical properties and corrosion behaviors of the Mg-10Gd-3Y-0.5Zr alloys cast in metal molds have been reported. However, there are few research reports about the sandmold casting magnesium alloys, especially for the corrosion behaviors.It is well known that an alloy produced by lowpressure sand-casting process has a different microstructure (as precipitation sequence, phase type and composition, grain size etc.) and mechanical behaviors compared to an alloy produced by permanent mold casting process due to the different cooling rate [10,11] , which will make the different casting alloys show different corrosion behaviors. Many extensive

Effect of aging treatment on corrosion behavior of Mg-4Nd-2Gd-0.5Zr alloy

“…However, the effect of aging treatment on the corrosion resistance of solid solution alloy varies with different alloy systems. Li et al [24][25][26][27][28] reported that aging treatment increased the numbers of cathodes in the galvanic corrosion and decreased the corrosion resistance of the solid solution alloy, but the results of the study on magnesium alloys by Gui et al [29][30][31] showed that appropriate aging treatment changed the distribution of second phase and increased the protective effect of second phase, and hence enhances the corrosion resistance.…”

(Y, Gd)H2 phase formation in as-cast Mg-6Gd-3Y-0.5Zr alloy

“…Mg-Gd-Y-Zr alloys have attracted increasing attention in the aerospace field because of their excellent mechanical properties in both room and elevated temperatures and excellent castability [1,2] . The quality of Mg-Gd-Y-Zr alloy castings is closely related to melting condition, solidification process and humidity in the surrounding environment [3,4] .…”