• Combined pre-compression and pre-aging yields the most refined and densest precipitate distribution, resulting in superior age-hardening performance in Mg-9.8Sn-3.0Zn alloy.
• Pre-aging alone enhances the number density of precipitates compared to direct aging, attributed to MgZn2 phases acting as heterogeneous nucleation sites for Mg2Sn.
• The synergistic effect of pre-compression-induced lattice defects and pre-aging-formed Mg3Sn/MgZn2 phases maximizes heterogeneous nucleation sites, leading to the highest precipitate density.
• The study provides a cost-effective strategy to improve the age-hardening response of Mg-Sn-Zn alloys, which is significant for lightweight high-strength applications.