Microstructure And Formation Mechanism Of Hot Dip Galvanized Layer Of High Strength IF Steel

Service life of high strength IF steel is usually extended by hot dip galvanizing.Coating properties and quality are influenced by coating structure.Coating structure and crystallographic texture are great influenced by hot dip galvanizing and alloying process.In this paper,coating structure and crystallographic texture of each phase under different galvanizing process were studied by Scanning Electron Microscope(SEM)and X-ray diffraction(XRD).The crystal orientation relationship between the substrate and coating was analyzed,which provided some experimental data and theoretical guidance for improving the quality of the coating.During 450-470 ℃ galvanizing process,Sandelin effect will be occurred in the test steel,the(?)phase of coating grows rapidly but the δ phase growth is inhibited.The structure of galvanized coatings is compact layer of b phase,columnar crystal layer of(?)phase,small sticks of(?)phase and η phase from inside to outside.After 490 ℃galvanizing process,the structure of galvanized coatings is compact layer of δ phase,granular mixed sturcture of(δ+η)phase,nubbly(?)phase,and η phase from inside to outside.With the increase of galvanizing temperature,the thickness of coating increases first and then decrease,and reaches the maximum at 470 ℃.With the increase of alloying temperature and time during the galvannealing,η phase diffuses inward until it disappears,(?)phase gradually disappears,δ phase eventually occupies the whole coating.The crystallographic texture of each phase of the coating shows that before galvannealing,r1 phase is mainly {0001} plane texture with higher intensity,(?)phase is mainly {010} and {20(?)} plane texture,δ phase is mainly {10(?)0} and {11(?)0} plane texture with lower intensity.The semicoherent interface is formed between {111} planes of the a-Fe and the {10(?)0} or {11(?)0} planes of the δ phase,and the coating is well combined with substrate.After galvannealing,the {0001} plane texture in r| phase decreases,the main testure of(?)phase changes into {132} plane texture and the intensity is weakened,the {10(?)0} and {11(?)0} plane texture of δ phase are decreasing and{10(?)8} plane texture is increasing,which cause the associativity between coating and substrate to become worse.