Mechanical properties and microstructures of the ZA-27 alloy with different contents of Mn are reported. Mn modifies the coarse foundry microstructure by forming Al-Mn precipitates and a fine lamellar alpha + beta microstructure. Additions of Mn increase the mechanical properties since coarse precipitates are avoided. Best results are obtained for the 0.25 to 0.30 weight% Mn range.