| Magnesium was the essential micro nutrient element for the human body, magnesium alloy can formed non-toxic soluble product, degraded in the body and excreted through its own body because of its good bioco MPatibility in the body fluid environment. And it had confirmed the bioco MPatibility of magnesium could be used in biomedical materials, so, magnesium alloy had become a promising human implant material. The purpose of this study was to develop a new type of biological material that could be used in biomaterial stent. However, it was known that corrosion resistance and mechanical properties of magnesium and magnesium alloys were poor, it was easy to corrosion and degradation in vivo with the metabolism of organisms excreted through the metabolism of organisms, which affected the magnesium alloy as a biological implant material application seriously. Therefore we choosed the nontoxic to humans of Zn, Zr and Ca as alloying elements o Mg-3Zn-0.3Zr-based alloy, adding a small amount in the base alloy of Ca herein, by alloying magnesium alloy to improve the overall performance, and the Ca content of different elements and different heat treatment process on the microstructure of magnesium alloy microstructure and the effect to improve the mechanical properties and corrosion resistance.The results showed that the microstructure, mechanical properties and corrosion resistance of alloys had produced significant changes with minor Ca addition or different heat treatment conditions.(1) The phases in alloys had changed significantly with the different amounts of Ca in the as cast alloys. ZK30 and ZK30-0.3Ca were mainly composed of α-Mg and Mg0.97Zn0.03 phase, ZK30-0.3Ca and ZK30-0.6Ca alloys were mainly composed of α-Mg, Mg0.97Zn0.03 and Ca2Mg6Zn3 phases with the further increase of Ca up to 0.6 wt%, the volume fraction of strip-like Ca2Mg6Zn3 phase increases with the further increase of element Ca. Furthermore, the grain size was refined gradually with the increase of Ca content.(2) In the Mg–3Zn–0.3Zr(ZK30)–Ca as cast alloys containing 0.3–0.9 wt-% Ca, the ZK30–0.6Ca presents the best mechanical properties due to the refined grain size and the second phase strengthening.(3) The Ca2Mg6Zn3 phase has great negative effects to the experiment alloys corrosion resistance. The ZK30–0.6Ca alloy has also the best corrosion resistance, which can be attributed to active effect of a balanced grain size and negative effect of the volume fraction of second phase Ca2Mg6Zn3 formed.(4) The as-prepared ZK30–0.6Ca alloy was subjected to solution treatment followed by artificial aging for different duration of time. The heat treatment conditions are solid solution for 48 h, and then aging for 0h, 2.5h, 5h and 10 h.(5) The heat treatment had influenced the microstructure of alloy. Heat treatment made Zr atoms diffuse towards into grains to form Zr-rich cores in the grain centre. The enrichment of zirconium in the grain centre leads to a higher corrosion resistance of this zone. The Zr-rich phases are protected in the process of corrosion as micro-anodes.(6) Heat treatment and microstructure influenced the corrosion rate of Mg-3Zn-0.3Zr-0.6Ca alloy under different conditions increase with the following order: F > T4 > T6-10 > T6-5 > T6-2.5 for long immersion time whereas T4 sample showed the best corrosion resistance in shorter time.(7) The T4 sample had the lowest corrosion rate due to almost second phases dissolve into Mg matrix, and few residual second phases are corroded after T4 treatment in shorter immersion time. However, the F sample had the highest corrosion rate due to the film broken down and the effect of second phases as micro-cathodes in long immersion time. |
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