MICROSTRUCTURE AND STRENGTH OF RAPIDLY SOLIDIFIED MAGNESIUM ALLOYS

Two kinds of magnesium alloys, Mg-5Al-0.5Si and Mg-5Al-1Y-0.5Si, were rapidly solidified by single-roll quenching to produce ribbons 3-5 mm wide and 50-100 mum thick. Microstructures of the ribbons consisted of long slender cells with a spacing of 0.3-0.5 mum and growing vertical ly from the chilled surface. They have a great deal of dislocations bu t no precipitates except for Mg2Si. Annealing of ribbons at 573 K for 10 ks led to a remarkable recovery and to the formation of very fine s ubgrains in the Mg-5Al-0.5Si alloy whereas the recovery was retarded i n the Mg-5Al-1Y-0.5Si alloy. The foil metallurgy technique to form a v ery thin sheet was useful for consolidation of rapidly solidified ribb ons. This technique gave rise to a good bonding between ribbons at 573 K and, at 70% reduction in thickness in air, a fine microstructure as sociated with dynamic recrystallization, and good mechanical propertie s. The effect of yttrium addition seemed to retard recovery and to pro mote dynamic recrystallization.