Abstract: Damping alloys serve as key materials in the domain of shock and noise reduction and find wide-ranging applications across several industries. Aluminum alloy, a commonly used engineering material, offers distinct advantages such as low cost and light weight. However, the damping property of aluminum alloy falls short of requisite standards. Thus, efforts toward enhancing the damping and mechanical properties of cast aluminum alloy carry considerable engineering implications. In this paper, the mechanical and damping properties of AlSi₁₀Sn₄Mg_x (x mass fraction is 0–4.0%) alloy have been investigated, and the mechanisms underlying the enhancement of the damping and mechanical properties have been analyzed by examining the effect of Mg on the wettability of Al/Sn and the alloy’s structure. The results of the mechanical property test reveal that the tensile strength of the AlSi₁₀Sn₄Mg_x alloy increases proportionally with Mg mass fraction within the range of 0% to 1.0%, whereas the fracture elongation undergoes a negligible change. With the Mg mass fraction rising to 1.0%, the tensile strength of the alloy reaches 161 MPa, and the fracture elongation stands at 3.4%. Subsequent increases in Mg content lead to remarkable enhancements in the strength of the samples. When the Mg mass fraction increases to 1.5%, the tensile strength of the alloy stands at 188 MPa, albeit with a remarkable decrease in fracture elongation. The damping properties of the alloy initially increase and subsequently decrease with the increase in Mg mass fraction. The alloy containing 1.0% Mg displays excellent damping properties at high temperatures and high frequencies. Specifically, the damping loss factor tanh at 25 ℃/1 Hz, 200 ℃/1 Hz and 25 ℃/40 Hz measures 0.038, 0.058, and 0.069, respectively. Further research suggests that the addition of a small amount of Mg can effectively improve the wettability of Al/Sn. The mean wetting angles of AlSi₁₀ and AlSi₁₀Mg₁ alloy samples with pure Sn are 141.2° and 116.8°, respectively. The exceptional wettability of Al/Sn facilitates the distribution of the small-sized β-Sn phase along grain boundaries within the AlSi₁₀Sn₄Mg_x alloy. Meanwhile, a small amount of Mg can also modify and spheroidize the eutectic Si phase in AlSi₁₀Sn₄Mg_x alloys, leading to the formation of the Mg₂Si strengthened phase. These two factors are primarily responsible for the excellent damping and mechanical properties of the alloy. However, excessive Mg will generate bulky Mg₂Si structures, which will impair the wettability of Al/Sn, leading to the deterioration of the damping and mechanical properties of AlSi₁₀Sn₄Mg₄ alloy.