Evolution of microstructure and mechanical properties of Mg-5.9Zn-1RE-0.6Zr alloy during extrusion process and aging process

The evolution of microstructure and mechanical properties of Mg-5.9Zn-1RE-0.6Zr alloy during extrusion and aging processes is investigated in the present article. The results show that a large number of the I phases, Z phases, W phases and other tiny precipitates (secondary phases) distribute on the matrix during the extrusion process. The extruded alloy shows excellent comprehensive mechanical properties with the tensile yield strength, ultimate tensile strength and elongation of 317 MPa, 360 MPa and 13.9 %, respectively. Subsequently, the extruded alloy is aged at 200 degrees C, 300 degrees C, 400 degrees C and 450 degrees C. The evolution of microstructure and mechanical properties clarifies that the alloy with low content of mixture of RE elements is a typical poor age-hardening MgRE-Zn alloy. The tensile yield strength, ultimate tensile strength and elongation of the peak-aged alloy are 333 MPa, 361 MPa and 8.8 % in the peak-aged alloy at 200 degrees C, respectively. The mechanical properties change little in the alloy aged at 200 degrees C compared with that of the alloy aged at 300 degrees C, 400 degrees C and 450 degrees C, which is mainly ascribed to the stability of the I phases during the aging process. Reversely, the I phases and the W phases transform to other intermediate phases and even dissolve back into the matrix during the aging process at 300 degrees C, 400 degrees C and 450 degrees C, which is the main reason for the strength decline of the alloy.

Automated summary

The evolution of microstructure and mechanical properties of Mg-5.9Zn-1RE-0.6Zr alloy during extrusion and aging processes was studied in this article. The presence of various secondary phases on the matrix was observed during extrusion. The extruded alloy exhibited excellent mechanical properties, with tensile yield strength, ultimate tensile strength, and elongation of 317 MPa, 360 MPa, and 13.9%, respectively. Aging at different temperatures revealed that the alloy with low RE element content is a poor age-hardening MgRE-Zn alloy. The mechanical properties of the alloy aged at 200 degrees C remained relatively stable compared to those aged at higher temperatures, attributed to the stability of the I phases.