The Phase Relations Of The Fe-Al-P Ternary System And The Galvannealing Process Of Zn-coating

In today's society, the phosphorus-coating steels are used in the modern automobile industry widely. The galvannealed-coating has the excellent corrosion resistance, paintability and weldability property. So the requirement of steels grow quickly in automotive industry. However, two kinds of coating layer peeling off will be distinguished for galvannealed coatings: flaking and powdering. In order to solve this problem well, the ternary phase equilibria at 450℃and 650℃of the Fe-Al-P system was determined. In this work, the influence of coating's growth in different galvannealing process was studied.The ternary phase equilibria at 450℃of the Fe-Al-P system was determined by equilibrated alloys using scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy(SEM-EDS) and X-ray diffractometry(XRD). There are six three-phase regions in the isothermal sections at 450℃, namely Bcc_A2+Fe3P+Fe2P, Bcc_A2+Fe2P+AlP, Bcc_A2+FeAl2+AlP, FeAl2+ Fe2Al5+AlP, Fe2Al5+ FeAl3+AlP and FeAl3+(Al)+AlP. The solubility of Al in the Fe3P, Fe2P phase, P in the Bcc_A2 phase and Fe in the AlP phase is low. There is little solubility of P in the phases of FeAl2, Fe2Al5, FeAl3 and (Al).The ternary phase equilibria at 650℃of the Fe-Al-P system were also studied in this work. The phase relation for Fe-Al-P system at 650℃is similar to it at 450℃. Three three-phase from experiment regions have been determined in this work, namely Bcc_A2+Fe2P+AlP, Bcc_A2+Fe2P+AlP and FeAl3+(Al)+AlP.In this work, the influence of coating's growth in different galvannealing process still was studied using scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy(SEM-EDS) and Smile View software. There are some results relating to the processes of 400°C -530°C, 530°C -400°C, 460°C -530°C and 530°C -460°C. In the 400°C -530°C and 460°C -530°C alloying process, theδ1p phase begins to grow in short time after the beginning of galvannealing. There is noζphase existing in the coating. In the 530°C -400°C and 530°C -460°C alloying process, there are someζphases in the coating. In the process of galvannealing , the speed ofδ1k phase growth accelerates when theη-Zn phase disappearance. The process of galvannealing from high temperature to low temperature is better for the growth ofδ1p than the process of galvannealing from low temperature to high temperature. It is better for the growth ofδ1p phase to rise the temperature of galvannealing process.