Study on the Precipitation Strengthening Mechanism of Mg–10Zn–5Al–0.2Sc Alloy

Abstract

The Mg–10Zn–5Al–0.2Sc (wt%) alloy was fabricated through gravity casting and subsequent heat treatment. The microstructure and precipitates of the alloy samples were meticulously examined using OM, SEM/EDS, and TEM/HRTEM. The results indicate that the microstructure of the alloy comprises a MgZnAl phase along with a minor presence of Al₂Sc. The incorporation of Sc serves to refine the grain size of the alloy while introducing vacancies and dislocations within the microstructure. After heat treatment, an abundance of rod-shaped nanoscale MgZnAl and MgZn phases precipitate within the grains, with these phases exhibiting a perpendicular relationship in terms of precipitation orientation, leading to the formation of numerous dislocations and planar defects. The nanoscale MgZnAl and MgZn phases, characterized by a hexagonally close-packed structure, contribute significantly (68.59%) to the enhancement of the yield strength of the heat-treated alloy. These phases demonstrate a degree of coherence with the α-Mg matrix, impeding dislocation motion, and effectively absorbing and storing dislocations, thereby mitigating strain and distortion concentrations within the phases during tensile deformation. This mechanism reinforces the strengthening effect of coherent interfaces, ultimately improving the strength and ductility of the alloy. After heat treatment, the alloy attains a tensile strength of 221 MPa, a yield strength of 208.45 MPa, and an elongation of 0.99%, representing enhancements of 33.13%, 38.88%, and 0.49%, respectively, compared to the matrix alloy.