Peritectic-Eutectic Transformation of Intermetallic in Zn Alloy: Effects of Mn on the Microstructure, Strength and Ductility

Zn alloy containing peritectic intermetallic compound usually has fine grains, so they show relatively high strength. But the intermetallic compound is coarse, which is blamed for the brittleness. In this work, a strategy to transform the peritectic intermetallic phase of Zn-Fe alloy into eutectic intermetallic phase is proposed by adding Mn. In detail, Mn co-precipitates with Fe and Zn to form a (Fe, Mn)Zn 13 phase, which provides nucleation substrate and increase the nucleation rate of the MnZn 13 eutectic phase because of their low interatomic and interplanar spacing misfit according to the edge-to-edge matching model. The intermetallic compound formed via eutectic reaction is finer than that formed by peritectic reaction. Results show that the intermetallic in Zn-Fe-Mn is refined by 79% compared with that of Zn-Fe. Moreover, the MnZn 13 phase forms a semi-coherent interface with negligible lattice misfit (0.09%) in (0111) orientation with Zn matrix, which is believed to decrease the intergranular fracture ratio. Consequently, Zn-Fe-Mn alloy has a compression yield strength, ultimate tensile strength and elongation of 135.98 MPa, 226.8 MPa, and 15.9%, respectively, which are 28%, 25% and 87% higher than those of Zn-Fe alloy. The strength is improved by dislocation shearing: lattice dislocations cut precipitates to advance through the alloy. The ductility is enhanced by dislocation transmission: dislocations transmit across the semi-coherent boundaries to eliminate the stress concentration. In addition, Lomer-Cottrell locks form with the interaction of dislocations, which not only pin the dislocation slip but also act as the FrankRead source to increase dislocation, resulting in excellent ductility.