Metastable bcc mischmetal-magnesium alloys

The bcc phase in the MM-Mg system can be metastably retained at room temperature for magnesium composition within the range 16 at. pct. - 20 at. pct. The retention of a lower composition was restricted by quenching rate and at higher concentrations by intermetallic compound precipitation. The lattice parameter for the pure bcc mischmetal phase was determined by extrapolation. The value obtained (a sub E = 4.131 A) was in good agreement with the theoretical value (a sub t = 4.156 A). Magnetic susceptibility data suggested that bcc mischmetal-magnesium alloys underwent a change from paramagnetic to antiferromagnetic behavior on cooling at approximately 20 K, independent of magnesium composition. The value found for the magnetic effective moment per gram-atom-magnetic-rare earth of each bcc MM-Mg alloy examined (MM - 16 Mg, MM - 18 Mg and MM - 20 Mg) was found to be constant (p sub eff was approximately 1.62 Mu sub B), independent of the magnesium composition. The observed Curie-Weiss temperature values decreasing with the magnesium content increasing were due to magnetic dilution. The equilibrium reaction bcc yields dhcp + MM Mg presented an undercooling effect of approximately 40 C around the eutectoid composition (approximately 17 at. pct. Mg). The sluggish character of this reaction was considered the strongest effect for the bcc structure retention in the mischmetal-magnesium system.