**2.2 Composition and microstructure characterization**

X-ray diffraction (XRD, Philips-X'Pert) using Cu Ka radiation was employed for the identification of the constituent phases in the as-cast Mg-Zn-Ca alloy and their corrosion products after immersion. Microstructure observations of the alloys were conducted on Olympus optical microscope. The specimens for optical microscopy were etched with a solution of 8 vol. % acetic acid for 30 s, thoroughly flushed with water and alcohol, and then dried by hot air.
