Experimental Research On Preparation And Properties Of Low Aluminum Permeability Layer

Aluminizing technology plays an important role in the fields of chemical industry,shipbuilding and electric power by virtue of its excellent high temperature oxidation resistance and sulfide corrosion resistance.At present,the aluminizing process has appeared in various forms after decades of development.As one of the most traditional processes,the pack aluminizing process has been widely used,but due to the more brittle phases of the aluminizing layer,heat treatment is necessary.In this paper,Q235 steel was selected as the base material,and the samples were subjected to diffusion annealing on the basis of pack aluminizing.First,the effects of temperature and holding time on the thickness and phase of the infiltration layer were studied.The experimental results show that with the increase of the diffusion annealing temperature,the thickness of the infiltration layer gradually increases,and the growth rate increases first and then decreases;the increase of the holding time also promotes the increase of the thickness of the infiltration layer.The thickening curve is parabolic,and the kinetic equations of thickening are summarized in combination with the experimental data of temperature and time.Considering the relationship between the phase and energy consumption,the optimal annealing process is determined to be 1000?and 6 hours.Secondly,a series of characterizations were performed on the samples,including the structure and phase composition of the infiltration layer,and it was found that FeAl and Fe3A1 phases were present in the infiltration layer.The hardness comparison test of the aluminized sample and the annealed sample showed that the hardness of the layer decreased significantly after annealing treatment,from 900HV0.1 to about 300-400HV0.1.A three-point bending test was used to legally analyze the bonding strength between the infiltration layer and the substrate.It was found that after the sample fractured,the infiltration layer was not found to fall off,and no cracking occurred between the infiltration layer and the substrate.Finally,Q235 samples,aluminized samples and annealed samples were selected for corrosion comparison experiments.It was found that in neutral NaCl solution,the annealed samples had the best corrosion resistance,and Q235 steel was prone to corrosion behavior;In acidic NH4C1 solution,the corrosion resistance of the annealed sample is also the best,and Q235 steel is prone to corrosion behavior;In strongly alkaline NaS solution,the adhesion of the surface corrosion products of Q235 steel hinders the reaction,so its corrosion resistance is the best,followed by the annealed sample.The aluminized sample is susceptible to corrosion in this solution.