A novel long-period phase in Mg97Yb2Cu1 alloy

Abstract

A Mg80Yb12Cu8 (CY) phase was found in a Mg97Yb2Cu1 alloy quenched after being annealed at 873 K for 10 min; the unit cell dimensions of the CY phase are described as 43×43×2 with respect to those of the original hcp-Mg lattice. The a-axis lattice constant of the CY phase well matches 43 times the a-axis length of the α-Mg phase. In the present work, the c-axis of the CY phase and the dendrite-like α-Mg phase in the precipitate zone are coaxial, i.e., the basal planes are coherent. This result is attributed to the good match between the lattice constants of the fundamental a-axis of the CY phase and the α-Mg phase. According to compression tests, the CY phase is responsible for the increase in strength observed in both the elastic and work-hardening regions in the Mg97Yb2Cu1 alloy. As far as our investigations of Mg97Yb2M1 (M = Al, Ni, Co) alloys, the phase similar to the CY phase have not found. Our discovery of this phase might provide a new path to the discovery of long-period superlattice in various Mg alloys.