Comparison study of Sn and Bi addition on microstructure and bio-degradation rate of as-cast Mg-4wt% Zn alloy without and with Ca-P coating

Mg-based implants, have useful properties such as biocompatibility, low density and elastic modulus close to natural bones eliminating of additional surgery for implant removal. On the other hand, they degrade rapidly in the early stage after implantation. This leads to some problems such as fast decreasing mechanical properties in a short time, aggregation of hydrogen bubble and gap formation between the implants and the tissue. This work aims at studying the effect of adding 0.5 wt% of Sn and Bi as alloying elements on the microstructure and in-vitro degradation behavior of as-cast Mg- 4 wt%Zn alloy without and with Ca-P coating. The evaluation process was achieved using optical and scanning electron microscopy, X-ray diffraction, in addition to the corrosion behavior using immersing process in simulated body fluid (SBF). The results showed clearly that the alloy containing Sn represents the lowest degradation rate, but the alloy containing Bi shows the highest degradation rate. In order to improve the degradation rate of the investigated alloys, coating with Ca-P using autocatalytic technique was applied. Coating process led to decrease the degradation rate of as-cast Mg-4wt%Zn and Mg-4wt%Zn-0.5 wt%Bi alloys, but it increased the degradation rate of Mg-4 wt%Zn-0.5 wt%Sn alloy. •The effect of Sn and Bi addition on microstructure of Mg-4Zn alloy is investigated.•The effect of Sn and Bi addition on bio-degradation rate of Mg-4Zn alloy is investigated.•Low degradation rate of Sn-added alloy as compared with Bi-added alloy is obtained.