This research described the identification phases by thermal analysis and microscopy inspection of Mg-xCa and Mg-0.5%Ca-xZn alloys that were solidified at slow cooling rate. Analysis of cooling curve after Ca addition shows the evolution of the Mg2Ca intermetallic phase at around 520 degrees C in addition to alpha-Mg phase. First derivative curves of alloys after the addition of Zn to Mg-0.5Ca alloy reveals three peaks related to alpha-Mg, Mg2Ca and Ca2Mg6Zn3 for alloys that have Zn/Ca atomic ratio less than 1.23. The peak of Mg2Ca reaction on the first derivative curves disappeared for alloys containing Zn/Ca ratio more than 1.23. A new peak was also observed at 330 degrees C for Mg-0.5Ca-9Zn which was identified as Mg51Zn20. Solid fraction at coherency point decreased with increasing Ca and Zn elements. However, coherency time and difference between the nucleation and coherency temperatures (T-N-T-DCP) increased by adding Ca and Zn in Mg-Ca and Mg-Ca-Zn systems. (C) 2011 Elsevier B.V. All rights reserved.