Effects of Ca and Ce Addition on Tensile and Fracture Properties in Squeeze Cast AT42(Mg-4Al-2Sn) Magnesium Alloys

摘要

The effects of the addition of Ca and Ce to the AT42(Mg-4Al-2Sn) alloy on the microstructural modification and deformation, as well as the fracture mechanisms of squeeze cast magnesium alloys, were investigated in this study. Microstructural analyses indicated that the AT42 alloy contained Mg_(17)Al_(12) and Mg_2Sn particles precipitated along cell boundaries, whereas long, needle-shaped CaMgSn particles were precipitated additionally in the AT42-0.5Ca and AT42-1Ca alloys. In the AT42-lCa-0.5Ce and AT42-lCa-lCe alloys containing Al_(11)Ce_3 particles as well as Mg_(17)Al_(12), Mg_2Sn, and CaMgSn particles, the overall distribution of precipitates was homogeneously modified considerably as the solidification cell size was refined. According to the observation of deformation and the fracture processes of the AT42-lCa alloys, the fracture proceeded mainly along cracked, needle-shaped CaMgSn particles at a relatively low stress-intensity factor level. However, in the AT42-lCa-lCe alloys, the deformation and fracture proceeded into cells rather than into cell boundaries as twins were developed actively inside cells, although few microcracks were initiated at the precipitates. Thus, the AT42-lCa-lCe alloy had the highest strength, ductility, and fracture toughness simultaneously because of the increase in the volume fraction of hard precipitates and the development of many twins in the Mg matrix.