Effect of Ca addition on microstructure and impression creep behavior of cast AZ61 magnesium alloy
(Department of Materials Engineering and New Technologies, Shahid Rajaee Teacher Training University, Lavizan, Tehran, Iran)
Abstract: Microstructure and creep properties of AZ61 alloy containing 1 and 3 wt.% Ca were investigated. The creep properties were examined using impression method under different stresses between 200 and 500 MPa at the temperature ranging from 423 to 491 K. The microstructure of AZ61 alloy contains α(Mg) matrix and Mg17Al12 intermetallic phases. It is shown that adding Ca to AZ61 alloy reduces the amount of Mg17Al12 phase via forming (Mg,Al)2Ca phase; furthermore, increasing the Ca content to 3 wt.% leads to the formation of (Mg,Al)2Ca phase, as well as the elimination of the Mg17Al12 phase. Creep properties of AZ61 alloy are improved with the Ca addition. The improvement in creep properties is attributed to the reduction in the amount of Mg17Al12 phase and the formation of (Mg,Al)2Ca phase with high thermal stability. According to the obtained creep data, it is concluded that the pipe diffusion-climb controlled dislocation creep is the dominant creep mechanism and Ca addition has no influence on this mechanism. The effect of pre-deformation on the creep properties of AZ61+3%Ca alloy reveals that the creep resistance of the alloy depends on the continuity of (Mg,Al)2Ca phase. It is decreased by reducing the phase continuity.
Key words: impression creep; magnesium alloy; Ca addition; dislocation creep; phase continuity