Study On Microstructure And Corrosion Of Mg/ZrO₂ Composites Prepared By Friction Stir Processing

As a low-density,biodegradable material,magnesium(Mg)and its alloys have attracted more and more attention in biomedical applications.As an implant,it needs to bear stress in animal body fluid environment.However,high corrosion rate of magnesium alloy limits the development and application as a medical implant.Through the preparation of magnesium matrix composites,the strength and elongation of magnesium matrix implants can be improved,and the corrosion resistance can be improved to a certain extent.ZrO₂ has good biocompatibility,high melting point and low thermal expansion coefficient.ZrO₂ particles can be used as reinforcement to prepare magnesium matrix composites,which can improve the deformation resistance of magnesium matrix composites and improve the corrosion resistance to some extent.In this study,Mg/ZrO₂ composite was prepared by friction stir processing(FSP).The AZ31 Mg alloy was research objects.In a large number of experiments,AZ31/ZrO₂ composite with uniform particle distribution was successfully prepared by 5 passes,and the corrosion resistant coating was prepared on the surface of composite by alkali heat treatment,The microstructure of the composite and coating was characterized by scanning electron microscope,the influence of alkali heat treatment temperature on the morphology and structure of the coating was analyzed.The tensile properties at room temperature of the composite were studied,and the static/dynamic corrosion properties of the composite and the prepared alkali heat treatment coating were evaluated comprehensively.The main conclusions are as follows:Compared with base metal(BM),the microstructure of AZ31/ZrO₂ composite is more homogeneous,densified and refined.During the FSP,not only dynamic recrystallization results in grain refinement of magnesium alloy,but also reinforced phase particles(ZrO₂)significantly refine the grain.The average grain size of FSP sample and AZ31/ZrO₂ composite is 3.1 ?m and 1.7 ?m? After alkali treatment,Mg CO3 crystals were formed on the surface of BM,FSP and AZ31/ZrO₂ composites,and the crystal size and shape were similar.After heat treatment at different temperatures,Mg CO3 crystal decomposes into dense Mg O by cracking.The higher the heat treatment temperature is,the faster the decomposition rate of Mg CO3 is.At the same time,Al in AZ31 magnesium alloy is oxidized to form Al2O3 during heat treatment,and the existence of Al2O3 will hinder the decomposition of Mg CO3.The results of immersion corrosion showed that the immersion corrosion rate decreased significantly and the corrosion resistance increased after alkali heat treatment.For AZ31/ZrO₂ composites,the resistance to immersion corrosion,electrochemical corrosion and stress corrosion is significantly higher than that of untreated samples.After alkali heat treatment,the immersion corrosion rate of the sample decreases significantly,and the formation of Al2O3 during alkali heat treatment will hinder the corrosion,which improves the corrosion resistance of the sample after alkali heat treatment.For AZ31/ZrO₂ composites after alkali heat treatment,the best heat treatment temperature for corrosion resistance is 500?.