Abstract:The microstructure and mechanical properties of Mg-9Al-0.8Zn(AZ91) alloys containing bismuth were investigated. Adding bismuth to AZ91 base alloys results in significant increase of tensile strength at both ambient temperature and 150℃, especially the creep rupture life at 150℃, while slight decrease of ductility. Microstructure observations indicate that the addition of bismuth modifies the microstructure of as-cast alloy and makes theβ(Mg17Al12) phase finer and more uniform in distribution. Furthermore, the discontinuous precipitation is suppressed greatly during aging process. When the bismuth addition amount exceeds 0.5%, rod-shape Mg3Bi2precipitates with hexagonal D52structure, which have high thermal stability and strengthen both the matrix and grain boundaries.

Key words: magnesium alloys; bismuth; microstructure; mechanical properties