Abstract: A high strength and high toughness magnesium alloy, characterized in that it is a plastically worked product produced by a method comprising preparing a magnesium alloy cast product containing a atomic % of Zn, b atomic % of Y, a and b satisfying the following formulae (1) to (3), and the balance amount of Mg, subjecting the magnesium alloy cast product to a plastic working to form a preliminary plastically worked product, and subjecting the preliminary plastically worked product to a heat treatment, and it has a hcp structure magnesium phase and a long period stacking structure phase at an ordinary temperature; (1) 0.5?a<5.0 (2) 0.5<b<5.0 (3) 2/3a?5/6?b.

Abstract: A high strength and high toughness magnesium alloy, characterized in that it is a plastically worked product produced by a method comprising preparing a magnesium cast product containing a atomic % of Zn, b atomic % in total of at least one element selected from the group consisting of Dy, Ho and Er, a and b satisfying the following formulae (1) to (3), and the balance amount of Mg, subjecting the magnesium alloy cast product to a plastic working to form a plastically worked product, and it has a hcp structure magnesium phase and a long period stacking structure phase at an ordinary temperature; (1) 0.2?a?5.0 (2) 0.2?b?5.0 (3) 0.5a?0.5?b.