Study On Corrosion Properties Of Rapidly Solidified Al-Ni Alloy

Al-Ni intermetallic compounds are widely used in engineering fields due to their advantages such as low atomic density,high compressibility,strong oxidation resistance and good corrosion resistance.Due to the high passivation tendency of aluminum,a dense passive film is easily formed on the surface of aluminum alloy,which exhibits excellent corrosion resistance in the atmosphere and fresh water.However,in the marine environment,due to the presence of chloride ions with small ionic radii and high penetrability,the oxide film can be easily destroyed,resulting in pitting corrosion,which leads to poor corrosion resistance of aluminum alloys.Therefore,the corrosion resistance of aluminum and aluminum alloys largely depends on the stability of the passive film on their surfaces and their ability to repair after the film is breached in a given environment.This article selects Al-Ni alloy as the research object to study how to improve its corrosion resistance in NaCl solution.(1)Effect of cooling rate and annealing on microstructure and corrosion resistance of Al50Ni50 alloyAl50Ni50 alloy ribbons were prepared by single wheel melt spinning method with circumferential speeds(Sc)of 21 and 42 m/s,and subsequently annealed at different temperatures.The microstructure and corrosion behavior of as-spun and annealed ribbons were investigated by a series of experiments.The experimental results show that the as-spun and annealed Al50Ni50 ribbons have single-phase crystal structure at two cold rates.With the increase of cooling rate,the as-spun and annealed ribbons with Sc=42 m/s have higher(100)crystal orientation factor F(100).This is because the increase of cooling rate and annealing treatment reduce the recrystallization barrier,which is conducive to the occurrence of recrystallization.The grain size of the ribbons with higher cooling rate is finer,which is conducive to the preferred orientation of crystals.The corrosion resistance of different ribbons was studied by electrochemical test and immersion experiment in 3.5%NaCl solution.The results showed that the ribbons with higher orientation factor F(100)had higher corrosion resistance.X-ray photoelectron spectroscopy(XPS)analysis showed that the as-spun ribbon with Sc=42 m/s had more stable and denser Al2O3+AlNi passivation film in the inner layer than the as-spun and annealed ribbons with Sc=21 m/s,and could be further enhanced by 700℃ annealing.The above results show that increasing the cooling rate and annealing at an appropriate temperature is conducive to the formation of stable and dense passivation film on the surface of Al-Ni alloy,thus improving its corrosion resistance.(2)Effect of Ni content on microstructure,mechanical properties and corrosion resistance of Al-Ni intermetallic compoundsAl3Ni2,AlNi and Al3Ni5 alloy ingots and ribbons were prepared by arc melting and single wheel melt spinning method.The effects of Ni content on their microstructure,mechanical properties and corrosion resistance were studied by various experimental methods.The results show that the three kinds of alloy ingots and ribbons with different Ni contents all have singlephase crystal structure.The ingots and ribbons show obvious liquid-solid heritability in terms of grain size and preferred crystal orientation.With the increase of Ni content,Ni element rapidly diverges at the grain boundary,which promotes the occurrence of recrystallization and makes the orientation of(100)crystal surface better,which is conducive to the formation of stable and dense passivation film on the surface of the ribbons.However,high Ni content will have an adverse effect on the thickness of the passivation film.The results of nanoindentation test show that with the increase of Ni content,the Young’s modulus of the ribbons increase gradually,but the hardness and wear resistance decrease gradually.The electrochemical test results show that the pitting potential and total impedance of the ribbons increase first and then decrease with the increase of Ni content.Therefore the corrosion resistance of the three alloys:AlNi>Al3Ni5>Al3Ni2.