Hot-dip Galvanizing Process Of Fe-Mn-Al-C Lightweight Steel And Study Of Coating Microstructure And Properties

The Fe-Mn-Al-C lightweight high-strength steels are perfectly suited to the light weight requirements of modern automobiles due to their high tensile strength,good plasticity and low density.In order to meet the automotive industry’s corrosion protection standards for high-strength steels,Fe-Mn-Al-C steels need to be hot-dip galvanized.However,because of the direct influence of alloying elements such as Mn and Al in this steel on its galvanizability,the galvanizing process and coating microstructure properties are an urgent engineering topic to be studied.This paper investigates the effects of annealing temperature in the continuous hotdip galvanizing simulation experiment and galvanizing temperature and dipping time in the batch hot-dip galvanizing experiment on their galvanizability using two different hot-dip galvanizing processes(continuous hot-dip galvanizing simulation experiment and batch hot-dip galvanizing experiment)using SEM,EDS and XRD analysis.In addition,neutral salt spray corrosion experiments were conducted on hot-dip galvanized Fe-Mn-Al-C steel obtained under the optimum process using a salt spray corrosion machine,aiming to investigate the corrosion behavior and corrosion mechanism of hot-dip galvanized Fe-Mn-Al-C steel and to evaluate the effect of hotdip galvanization on the corrosion resistance of Fe-Mn-Al-C steelAs the annealing temperature increases during the continuous hot dip galvanizing process(500℃→600℃),the oxidation of Mn elements in the substrate increases and the grain size of Fe-Al phase in the suppression layer increases(0.9～1.2μm→2.4～2.8μm),resulting in increased "leakage" on the surface of the substrate and reduced galvanizability.During the batch hot dip galvanizing process,the time of Fe2Al5 inhibition layer generation showed a regular negative correlation with the increase of galvanizing temperature.And with the increase of impregnation time,the damage of Fe2Al5 inhibition layer gradually increased and lost its inhibitory effect on Fe-Zn reaction.As the galvanizing temperature increased(460℃→520℃),the thickness of the galvanized layer increased and then decreased;the hardness of the specimen decreased and then increased;at 490℃,the quality of the galvanized layer was the best and the bonding force was the best.With the increase of dipping time,the thickness of galvanized layer increases and then decreases;the hardness of specimen decreases and then increases;at3 min,the quality of galvanized layer is the best and the bonding force is the best.In the salt spray environment,the corrosion products formed on the surface of FeMn-Al-C steel are oxides of iron,manganese,aluminum and composite oxides of manganese-aluminum,of which Fe2O3 is the main component of iron rust.The corrosion products of hot-dip galvanized Fe-Mn-Al-C steel are mainly Zn5(OH)8Cl2-H2 O and Zn5(OH)6(CO3)2,of which Zn5(OH)8Cl2-H2 O has an extremely strong protective effect on the substrate.During the whole corrosion process,the corrosion rate of galvanized sheet showed a trend of first increasing,then leveling off,and then decreasing.