<p>This work explores the tribological performance of AZ91M magnesium alloy fabricated via Cold Metal Transfer–Wire Arc Additive Manufacturing (CMT-WAAM) under varied heat input conditions. As a lightweight structural material, AZ91M offers excellent strength and corrosion resistance but poses fabrication challenges due to its hexagonal close-packed structure and thermal sensitivity. The CMT-WAAM technique provides a promising pathway to overcome these limitations, enabling precise heat control and near-net-shape manufacturing. Three distinct heat inputs—low, medium, and high—were investigated to assess their influence on microstructure, mechanical response, and wear resistance. Results revealed that medium heat input led to refined equiaxed grains and uniform β-Mg₁₇Al₁₂ and η-Al₈Mn₅ phase distribution, while both low and high inputs resulted in coarser or segregated structures. Mechanical analysis confirmed that medium heat input yielded an ultimate tensile strength of 425&#xa0;MPa, compressive strength above 500&#xa0;MPa, and average hardness of ~ 95 HV, compared to 370–390&#xa0;MPa tensile strength and 80–88 HV hardness under low and high heat inputs. Tribological tests demonstrated that medium heat input provided a ~ 23% reduction in wear mass loss and ~ 31% lower coefficient of friction, together with a lower temperature rise during sliding. These improvements are attributed to improved phase stability and surface integrity. FESEM analysis of worn surfaces and debris supports a transition in wear mechanisms-from brittle fracture and delamination at extreme heat inputs to stable abrasive wear with plastic deformation under medium heat input condition.</p> Graphical Abstract <p></p>