The Influence Of Ti And Mn On Interface Reaction Of High Strength Low-alloy Steel With Hot-dipping Al-Zn

On the situation of resource conservation and environmental protection in China,the demanding for high strength low-alloy steel with hot-dipping Al-Zn alloy layer aremore and more in building industry. However, high strength low-alloy steel, due tocontain lots of Mn elements, will interact with Al-Zn alloy in hot-dipping process. Itwill appear series of quality problems. That makes its application in building industry berestricted. Based on mild carbon steel with hot-dipping55wt.pct Al-Zn-1.6wt.pct Sialloy technology, this work was carried out by investigating interaction of elements in55wt.pct Al-Zn alloy and steel plates.First of all, the influence of Ti on interface reaction for high strength low-alloysteel （H420） with hot-dipping55wt.pct Al-Zn-1.6wt.pct Si alloy were studied bycomparing microstructure, elemental distribution, phase composition and growthkinetics of interface reaction layer with different55wt.pct Al-Zn alloy. The resultshowed that, the microstructure, elemental distribution, phase composition of interfacereaction layer were almost same. Meanwhile, the growth mechanism of interfacereaction layer was characterized. It was showed that the growth rate of interface reactionlayer followed the parabolic law, Ti addition decreased thickness of interface reactionlayer and Fe₂Al₅layer about3.25μm and1.83μm.Secondly, the influence of Mn in H420steel on interface reaction for high strengthlow-alloy steel with hot-dipping55wt.pct Al-Zn-1.6wt.pct Si alloy were investigated bycomparing microstructure, elemental distribution, phase composition and growthkinetics of interface reaction layer with different steel plates. The result showed that, nonew pahse formation, Mn exsited in interface reaction layer in the form of solid solution.Besides, carbon build-up existed in H420+GL interface reaction layer, and it is obviouswith reaction time. Meanwhile, the growth mechanism showed that the growth rate ofinterface reaction layer followed the parabolic law, the thickness of interface reactionlayer and the thickness of Fe₂Al₅phase were all lower. The thickness of Fe₂Al₅phase decreased large, the average is about2.72μm.To deeply interpret the mechanism of Mn on interface reaction, the first-principlesmethod was performed to calculate the optimized structure, bond-energies andelectronic structure of Mn substitution in Fe₂Al₅phase. The result showed that, theenergies of Mn substitution at Al sites are lower than the energies at Fe sites with avalue of5.5eV in the Fe₂Al₅phase. the net electronic charges of Fe atom decreaseabout0.006eV, but the net electronic charges of Mn atom are greatly higher. Itindicates that the electronic charge of Al atom transfer to Mn atom more significantlythan to Fe atom.Finally, we study solid solubility of Ti in55wt.pct Al-Zn-1.6wt.pct Si alloy atdifferent temperature, and relationship of different Ti addition with its actual content in55wt.pct Al-Zn alloy, by Ti addition in high temperature bath for long time balancedprocess. The results show that, the solid solubility of Ti in55wt.pct Al-Zn-1.6wt.pct Sialloy is very low. The solid solubility of Ti in55wt.pct Al-Zn-1.6wt.pct Si alloy is0.04wt%at650℃; and solid solubility is0.029wt%at600℃.