Microstructure of MgAl5Ca3Sr alloy after creep deformation and high‐temperature heat treatment

Abstract

The paper presents results of microstructural investigations of MgAl5Ca3Sr magnesium alloys in the as‐cast condition, after creep tests at 180 °C, and after heat treatment at 450 °C for 4.5 hours. The microstructure of MgAl5Ca3Sr alloy is composed of α‐Mg solid solution, irregular shaped (Mg,Al)2Ca phase with C36 crystal structure, bulky (Mg,Al)17(Sr,Ca)2 phase, fine lamellar Mg2Ca phase with C14 structure, needle‐shaped Al2Ca precipitates with the C15 crystal structure. The precipitation of the needle‐shaped Al2Ca phase in the α‐Mg grains and spheroidization of the C14 phase were found after heat treatment at 450 °C in argon atmosphere. The (Mg,Al)2Ca (C36) and (Mg,Al)17(Sr,Ca)2 phases seems to be stable at 450 °C, however, the increasing of aluminum content in C36 compound was observed suggesting the initial stage of C36 → C15 transformation. After creep deformation at 180 °C precipitates of the Al2Ca phase were found in α‐Mg phase. The intermetallic compounds are stable at 180 °C. The MgAl5Ca3Sr alloy exhibits good creep resistance up to 75 MPa. Tensile properties are comparable to those of Mg‐RE‐Zn–Zr alloys.

Microstructure and Creep Properties of Selected Gravity Casting Magnesium Alloys

“…A good alternative for Mg-Zn-RE alloys is available in the newest Mg-Al-Ca alloys. After gravity casting and suitable modification of the molten metal the mechanical properties of these alloys are comparable to those of expensive Mg-RE-Zn-Zr (ZRE1) alloys (tensile strength about 140 MPa and yield strength about 90 MPa) [18]. Calcium exerts a positive effect on the creep resistance of Mg-Al alloys.…”

“…Moreover, the calcium boasts the low density and cost [2]. The creep resistance of Mg-Al-Ca alloys may also be heightened by the addition of strontium due to solid solution strengthening [18]. Aluminum in Mg-Al-Ca alloys improves the mechanical properties at ambient temperature and casting properties.…”