<p>The age-hardening response and related precipitate microstructure in Mg–Pb alloys with different Zn contents have been examined systematically. The age-hardening response significantly improves with increasing Zn content. Specifically, the addition of 3 wt% Zn results in a twofold increase in hardness increment, from 9.7 to 21.3 HV, during ageing at 160&#xa0;°C. The precipitation kinetics is also facilitated, leading to a shorter time to reach peak hardness from 3000 to 200&#xa0;h. The enhanced age-hardening response is attributed to the threefold increase in the number density of γ-Mg₂Pb precipitates and the uniform contribution of rod-like Zn-rich precipitates in the Mg–Pb–Zn alloy. In the Zn-free alloy, γ precipitates typically have a basal lath-like morphology, whereas in the Mg–Pb–Zn alloy, prismatic and pyramidal γ lath precipitates are also frequently observed, leading to the formation of two types of novel orientation relationships. Zn solute atom segregation is detected at the γ precipitate/matrix interface, which slows the coarsening rate, refines precipitate size, and hence increases the number density of γ precipitates by a factor of three in the Mg–Pb–Zn alloy. Additionally, each γ precipitate always contacts with a rod-like precipitate in the peak-aged samples. Microstructure characterization performed at the early stage of ageing suggests that rod-like Zn-rich precipitates act as abundant heterogeneous nucleation sites for γ-Mg₂Pb precipitates, which should be another reason for the refinement of γ precipitate in the Zn-containing alloys. These results provide new insights into the development of novel precipitation-hardenable Mg alloys via micro-alloying elements.</p> Graphical abstract <p></p>