Preparation,Degradation And Mechanical Properties Of Bioglass Coatings On Surface Modified Magnesium Alloy

Magnesium and its alloy have been considered as a promising biodegradable bone implants due to their good biocompatibilities, mechanical properties and biodegradability. However, magnesium alloys have rapid degradation rates in chloride containing environment, leading to the excess of Mg2+ ions, the release of hydrogen and high pH values. These problems limited biomedical applications of magnesium alloys. Therefore, it is very important to control the degradation rates of magnesium alloy effectively without damaging the inherent corrosion resistance and the mechanical properties of the magnesium alloy. Surface modification with appropriate coatings on Mg alloys is regarded as an effective method to improve the corrosion resistance.This work was conducted based on the successful preparation of 45S5 bioactive glass-ceramic coatings on AZ31 magnesium alloys through sol-gel dip-coating method. The influence of heat treatment during preparation on the inherent corrosion resistance and mechanical properties of AZ31 substrates was investigated. The effects of acid or alkaline treatments on interface bonding strength and corrosion resistance of coated AZ31 magnesium alloys were also studied. Finally, the corrosion resistance and mechanical properties of coated samples under pressure were initially studied.The results showed that AZ31 magnesium alloy can withstand around 500°C heat treatment, without obvious loss of corrosion resistance and mechanical properties. The pretreatment of magnesium alloy substrates by acid or alkaline is beneficial to prepare the compact and crack-free 45S5 bioactive glass-ceramic coatings on AZ31 Mg alloys. Meanwhile, an interlayer was formed that resulted in a great improvement of the interface bonding strengths between substrates and coatings, and also provided a better protection to substrates. Electrochemical and immersion tests revealed that 45S5 bioactive glass coated magnesium alloy prepared by HF pretreatment showed the best corrosion resistance.Axial compression was conducted on coated samples with three different coatings. It was found that cracks appeared on all the three kinds of coatings after applied pressure for some time. When the applied pressure is 0.5 MPa, the initial corrosion rates of samples were lower than that of unpressurized samples. After 12 days of immersion in SBF, the axial compressive strengths of all coated specimens dropped nearly 10%.