Study On Microstructure And Corrosion Behavior Of Mg-Li Alloy

Mg-Li alloys are the lightest metals in industrial applications,with high strength,good plasticity,high energy particle penetration,biocompatibility and other characteristics.And it is the most suitable and potential materials of the aerospace,military weapons,clinical medicine,automotive,nuclear industry.With the development of industrial production,the demand for lightweight materials become higher,Li as a kind of low density metal can greatly reduce the density of magnesium alloy,Mg-Li alloy has attracted more and more attention.However,the chemical activity of Li is higher,and the corrosion behavior and corrosion mechanism of Mg-Li alloys need to be further studied.In this paper,the microstructures and mechanical properties of cast,annealed and rolled Mg-Li alloys(Mg-3Li,Mg-8Li,Mg-14 Li,mass fraction)were studied by XRD,metallographic microscope and micro Vickers hardness tester.The effects of Li content on the corrosion behavior of annealed and rolled Mg-Li alloys in 0.1M NaCl solution were investigated in detail by potentiodynamic polarization,galvanostatic hydrogen evolution,scanning electron microscopy and transmission electron microscopy.The following conclusions can be summed up by the research.(1)The microstructure of cast Mg-3Li alloy and Mg-14 Li alloy is composed of single ? phase or ? phase,while the Mg-8Li alloy is composed of two phases,and the acicular ? phase is distributed in the ? phase.The hardness of the alloy decreases from 54.5HV to 37.7HV with the increase of Li content.After the annealing treatment(Mg-3Li alloy and Mg-8Li alloy homogenization annealing at 350? for 8h,Mg-14 Li alloy was treated by 380?,5min solid solution and 350 ?,8h homogenization annealing),the dendrite of Mg-Li alloys disappeared,the grain size of Mg-3Li alloy and Mg-14 Li alloy were 108.6 ?m and 187.9 ?m,respectively..(2)After annealing treatment,the corrosion behavior of Mg-Li alloys in 0.1M NaCl solution showed that the corrosion resistance of Mg-3Li alloy was better at the initial stage of immersion,and the corrosion rate of Mg-8Li alloy was the largest.In 0.1 M NaCl solution,the corrosion characteristics of Mg-3Li alloy and Mg-14 Li alloy alloy was pitting corrosion,due to the potential difference between the ? and ? phase,the ? phase is preferential corroded and appear obvious filiform corrosion.(3)After a long time of immersion,the corrosion products on the surface of Mg-3Li alloy are distributed with a large number of cracks,while the corrosion products of Mg-14 Li alloy are relatively compact.This is because the corrosion product of Mg-3Li alloy was Mg(OH)2,while the corrosion product of Mg-14 Li alloy is composed of Li2CO3.Cl-can destroy the Mg(OH)2 film which makes the activation center appears on the surface the and accelerates the corrosion of magnesium alloy.The Li2CO3 film on the surface of Mg-14 Li alloy can be more stable in NaCl solution.(4)The Mg-Li alloy(Mg-3Li,Mg-8Li,Mg-14Li)was treated by hot rolling(250 ?,under the pressure amount of 70%),and the grains were elongated along the rolling direction.The hardness of Mg-3Li alloy and Mg-8Li alloy was increased from 54.5HV and 42.3HV to 75.2HV and 52.3HV,respectively.The hardness of Mg-14 Li alloy was increased from 37.9HV to 39.3HV due to the small degree of hardening.(5)The corrosion rate of rolled Mg-3Li alloy is the smallest,and the corrosion resistance of Mg-8Li alloy is the worst.The results show that rolling process main affect the anodic process of Mg Li alloy.The corrosion product film is an important factor affecting the corrosion behavior of magnesium alloy,compared the corrosion product film of rolled Mg-3Li with annealed Mg-3Li alloy,the product film was more density,which is due to the rolled Li spread more easily,Li2CO3 to fill the gap in the film.