High strength Mg-1.4Gd-1.2Y-0.4Zn sheet and its strengthening mechanisms

A high strength Mg-1.4Gd-1.2Y-0.4Zn (at%) alloy sheet was successfully prepared by the combination of extrusion and corresponding heat treatments. The microstructure, texture and mechanical properties were systematically investigated. The results show that the microstructure of the as-extruded alloy is composed of finer recrystallized grains with random orientation, elongated grains, and 14H-LPSO structures which are parallel to the extrusion direction, possessing a modified texture. For the as-aged alloy, the metastable β′ phases dispersively distribute within the grains. The as-extruded alloy already shows high tensile mechanical properties. After aging treatment, the tensile yield strength, ultimate tensile strength, and elongation to failure reach 395 MPa, 461 MPa, and 6.0%, respectively. The solution treatment and extrusion, which give rise to the dissolution of eutectic phases, the grain refinement and the accumulation of dislocations, contribute mainly to the strength of the as-extruded alloy. Aging treatment further strengthens the alloy by precipitating the metaphase β′ at the expense of the rare earth element dissolving into the matrix.