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D ue to low Young's modulus (~45GPa), low density (1.7-2.0 g•cm-3), and good biodegradable properties, magnesium and magnesium alloys are in a region of interest as potential orthopedic, craniofacial, and cardiovascular materials [1]. Many researchers are currently developing new biodegradable magnesium alloys and investigating all kinds of properties [2]. Among all the alloys, Mg-Zn-Ca especially attracts the scientists' attention because of their high strength (yield strength>200 MPa, ultimate tensile strength>250MPa), high ductility (elongation>20%), moderate bio-corrosion properties, and good biocompatibility [3, 4]. Summarizing the development status of Mg-Zn-Ca alloys, it is found that Zn content generally surpasses or equals to 4wt.% if Ca addition is less than 1wt.% [1,5-13] or Zn concentration <10wt.% if Ca addition is ≥1wt. % [14-20]. The purpose of high Zn addition is to ensure high mechanical properties by solid-solution strengthening, grain boundary strengthening and precipitation strengthening, while the role of Ca is to refi ne the grain size and enhance the ignition point [21]. However, it is also noted that high Zn or high Ca concentration is generally detrimental to corrosion resistance [15, 22-25]. Therefore, the growing trend in