Study On Corrosion Properties Of AZ91-TiO₂@CNTs Composites By Rare Earth Pr And Heat Treatment

Carbon nanotubes(CNTs)are widely used to improve the mechanical properties of magnesium alloys due to their high strength and elastic modulus,while rare earth elements are also widely used to improve the morphology and distribution of various phases in the microstructure.Therefore,CNTs and rare earth Pr are used as reinforcing phases to make magnesium matrix composites.In this paper,TiO2 coated CNTs and powder metallurgy have been used to improve the dispersibility of CNTs in AZ91 magnesium alloy and the interfacial bonding strength with the matrix.The corrosion resistance of AZ91-TiO2@CNTs composites is improved by adding rare earth Pr and T6 heat treatment.AZ91,AZ91-Pr,AZ91-Pr-1.0 wt.%CNTs,AZ91-Pr-TiO2@xCNTs(x=0.5,1.0,and 1.5 wt.%)were prepared by ball milling and vacuum hot sintering,and the microstructure,microhardness and corrosion were analyzed by comparison Performance changes.The main conclusions are as follows:(1)Adding 1 wt.%of rare earth Pr and CNTs to AZ91 alloy can refine the a-Mg phase in the alloy,the ?-Mg17Al12 phase is reduced and uniformly distributed in the matrix,and there is a small amount of agglomeration at the grain boundary CNTs.The rare earth intermetallic compound formed in the AZ91-Pr composite is Al11Pr3 phase.The microhardness of AZ91-Pr(78.2 HV)and AZ91-Pr-CNTs(82.4 HV)composites has increased by 8.6%and 14.4%compared to the matrix,respectively.The self-corrosion current density of AZ91-Pr is 37.5%lower than that of the matrix(0.24 mA·cm-2),and 34.8%lower than that of the AZ91-Pr-CNTs composite(0.23 mA·cm-2).The addition of CNTs improved the microhardness of AZ91 alloy,but made the corrosion performance of the alloy worse.The addition of rare earth Pr improves the microhardness and corrosion performance of AZ91.(2)The TiO2 coated CNTs were added to the AZ91-Pr composite material.The microstructure and microhardness of the composite material were optimized when the addition amount was 1 wt.%,And the optimal value of microhardness was 86.1 HV,corrosion current density is 0.21 mA·cm-2.TiO2@CNTs can make CNTs well dispersed,and to some extent improve the microhardness and corrosion resistance of AZ91-Pr-CNTs composites.(3)The AZ91-Pr-1.0 wt.%TiO2@CNTs composite was subjected to T6 heat treatment.The distribution of the microstructure of the composite and the refinement effect of the ?-Mg phase were optimized at 12 h,and the corrosion current density was 0.16 mA·cm-2,which shows that heat treatment can effectively improve the corrosion resistance of composite materials.(4)The addition of rare earth Pr,coated TiO2 and heat treatment are beneficial to better dispersion of CNTs in the matrix and to make the ?-Mg and ?-Mg177Al12 phases in the alloy more refined and improve their distribution at grain boundaries,so that the alloy is in the corrosion process The local potential is reduced and no huge corrosion pits are formed.The addition of CNTs enhances the surface potential of the alloy,which will form strong micro-galvanic corrosion in the alloy,and the addition of rare earth Pr forms Al11Pr3 phase in the alloy,which will hinder the micro-galvanic corrosion between CNTs and the magnesium matrix to a certain extent.happened.Therefore,choosing AZ91-Pr-1.0 wt.%TiO2@CNTs composite material after heat treatment as the modified AZ91 alloy selection material not only significantly improves the microhardness of the alloy,but also improves the corrosion performance of the alloy to a certain extent.