The effects of Ca and Mn on the microstructure, texture and mechanical properties of Mg-4 Zn alloy

Abstract

• A good atom matching orientation relationship of ( 2 ¯ 1 ¯ 1 ¯ ) Mn //(1 2 ¯ 11) Ca2Mg6Zn3, 〈 2 ¯ 5 1 ¯ 〉 Mn //〈1103〉 Ca2Mg6Zn3 has been detected, which provided the heterogeneous nucleation site of Ca 2 Mg 6 Zn 3 phase particles. • The conventional texture weakening effect of Ca element was suppressed by the addition of Mn due to the increased friction of unDRXed area. • A model of strengthening was used to evaluate the contribution of strength from grain boundary strengthening, precipitate strengthening and dislocation strengthening. • One of the best element rations was detected at 0.6 wt.% Ca and 0.7 wt.% Mn (Mg-4Zn-0.6Ca-0.7Mn), which matched a good combination of ultimate tensile strength (320 MPa) and elongation (16%). The microstructural evolution, texture and mechanical properties of nine Mg-4Zn-xCa-yMn alloys ( x = 0.3, 0.6, 1.0; y = 0.2, 0.3, 0.7 wt.%) were investigated systematically. Alloying with Ca and Mn refined the grains of the extruded sheets and increased the unDRX fraction. Mn could be the heterogeneous nucleation site of Ca 2 Mg 6 Zn 3 phase because of a good atom matching at the orientation relationship of ( 2 ¯ 1 ¯ 1 ¯ ) Mn //(1 2 ¯ 11) Ca2Mg6Zn3, 〈 2 ¯ 5 1 ¯ 〉 Mn //〈1103〉 Ca2Mg6Zn3 . The traditional texture weakening effect of Ca was strongly decreased for the simultaneously addition of Mn. With increasing Ca and Mn concentration, the strength increased and ductility decreased. Mg-4Zn-0.6Ca-0.7Mn exhibited a good combination of ultimate tensile strength (320 MPa), yield strength (286 MPa) and elongation (16%). A model of strengthening indicated that grain boundary strengthening and precipitate strengthening made a large contribution to the strength of Mg-4Zn-0.6Ca-0.7Mn. In addition, the dynamic recrystallization, texture modification and the strengthening effect from different parts also have been analyzed in detail.