Age-Hardening Behavior and Phase Transformation of Mg-9.2Gd-1.9Y-1.8Zn-0.5Zr Alloy

In this study, the age-hardening behavior and phase transformation of an Mg-9.2Gd-1.9Y-1.8Zn-0.5Zr alloy were systematically investigated. Results showed that the alloy exhibits substantial strengthening effects during aging at 225°C. During the under-aging stage, the second phases mainly undergo nucleation, supplemented by growth. In the peak aging stage, both nucleation and growth of the second phases occur simultaneously. Many main strengthening phases ( β ′ and β 1 phases) precipitate, leading to a 21.7% increase in alloy hardness at its peak. During the over-aging stage, the second phases predominantly undergo growth, accompanied by nucleation. As the aging time increases, the size of the β 1 phases increases and transforms to stable β phases, resulting in a decrease in alloy hardness. Subsequently, the alloy experiences the accumulation of β and LPSO phase, and the lamellar LPSO phases transform into block LPSO phases.