A New Intermetallic Compound Mg1.75Cu1.0Al0.4

Abstract

Magnesium-based alloys are important for hydrogen storage applications [1, 2]. In our previous study [1], using X-ray diffraction (XRD) analysis, we found that the alloy of nominal composition Mg1:8Cu1:0 Al0:2 contains Mg2Cu, MgAl2 and an unknown phase. The interplanar spacings (d values) of this unknown phase correspond closely with the data of the JCPDS (Joint Committee on Powder Diffraction Standards) card of MgCuZn [3]. To obtain the composition of the unknown phase, a series of Mg±Cu±Al compositions were prepared and analyzed. Because the melting points of Mg and Al are low (Mg melts at 650 8C, Cu at 1084.5 8C and Al at 660.1 8C) [4], and Mg is volatile at high temperatures, the method of preparing the alloy is as follows. The initial metals Mg, Cu and Al (all of 99.99% purity) were prepared in an induction furnace (1000 Hz 13 kW Balzers, Switzerland) under a static argon atmosphere (about 1 atm) of 99.99% purity. Copper was melted ®rst in an alumina crucible, then magnesium and aluminum were added. The temperature was maintained at 800 8C for 5 min so that the initial metal reacted ef®ciently, then the alloy was cooled naturally to room temperature in the furnace. To compensate for the volatile loss, the initial metal Mg was prepared with an excess of 1.5 wt % more than the target composition. The alloy was pulverized mechanically into powder of 300 400 mesh and was analyzed by XRD using a Rigaku D=max-rA X-ray diffractometer employing graphite-monochromed CuKa radiation at room temperature. The interplanar spacings plane (d values) of the alloys were calculated according to the Bragg Formula: