Microstructure, mechanical properties, corrosion behavior and cytotoxicity of Mg–Zn–Al–Ca alloys as biodegradable materials

• The effects of the addition of Al to Mg–4Zn–0.2Ca alloy were investigated.
• The addition of Al up to 3 wt.% to the alloy modified its properties.
• The modifications in the properties were ascribed to the microstructure refinement.
• The addition of Al more than 3 wt.% led to considerably deteriorated properties.
• This deterioration was attributed to the formation of the secondary phases.

Recently, considerable attentions have been paid to alloy Mg–4Zn–0.2Ca for biomedical applications due to its suitable biocompatibility and acceptable mechanical properties. In this work, the effects of the addition of different amounts of Al on microstructure, mechanical properties, degradation behavior, and biocompatibility of this alloy were investigated. The corrosion behaviors of the alloys were investigated through polarization tests, chronoamperometry analysis, immersion tests, and EIS experiments. The mechanical properties were analyzed by using tensile tests and compression tests. The results showed that the addition of Al up to 3 wt.% considerably modifies the degradation behaviors and the mechanical properties of the alloys due to its positive effects on microstructure refinement. On the other hand, the addition of more quantities of Al leads to the formation of considerable amounts of secondary phases in the grain boundaries of the alloys, leading to noticeably deteriorated properties. Mechanical tests showed that the addition of Al (up to 3 wt.%) increases the UTS of the alloys from 157 MPa to 198 MPa. Moreover, in vitro corrosion tests in SBF solution revealed that with the addition of Al up to the above mentioned value, the corrosion current densities of the alloys decrease from 134 μA cm−2 to 22 μA cm−2, and Mg–4Zn–3Al–0.2Ca exhibited the lowest obtained degradation rates in different immersion and electrochemical experiments. Cytotoxicity assessments also indicated the good biocompatibility of this alloy, making it a suitable candidate for further considerations as a degradable metallic biomaterial.