Precipitate phases in the Mg-4Y-4Sm-0.5Zr alloy

Precipitate phases in the Mg-4Y-4Sm-0.5Zr alloy have been characterised using TEM. The precipitation sequence in the Mg-4Y-4Sm-0.5Zr alloy involves formation of phases as β′-β1-β. The β′ precipitates were formed within the grains when the alloy was aged at 473 K. This intermediate β′ phase is thermally stable at 473 K. The globular shape β′ precipitates were formed in the under aged state at 473 K. These globular shape β′ precipitates coalesced, and the plate shape β′ precipitates were formed lying in the {2 1¯ 1¯ 0} habit planes with increasing ageing time. The much bigger equilibrium β precipitates with fcc crystal structure were directly precipitated on the grain boundaries at 473 K. The β1 precipitates were formed within the grains when the alloy was aged at 523 K. These plate shape β1 precipitates lied in the {1 0 1¯ 0} habit plane and in contact with β′ precipitates. The plate shape equilibrium β precipitates with fcc crystal structure precipitated along the {1 0 1¯ 0} habit plane when the alloy was aged at 573 K. The orientation relationship between β and the Mg matrix is: [1 1 1]β||[2 1¯ 1¯ 0]a, (2¯ 2 0)β||(0 0 0 1)a.