摘要
利用SEM观察了22Mn B5钢在900℃不同奥氏体化时间下,热镀Al-10%Si(质量分数)镀层的微观组织变化情况,利用EDS和GD-OES分析了奥氏体化后热镀Al-10%Si镀层的元素分布。结果表明,22Mn B5钢奥氏体化前,热镀Al-10%Si镀层主要由纯Al、纯Si和二者共晶反应形成的金属间化合物Fe_2SiAl_7组成,在Fe_2SiAl_7和钢基体之间存在一层薄薄的由Fe2Al5和FeAl_3组成的化合物层。900℃奥氏体化后,热镀Al-10%Si镀层中的三元共晶相Al+Si+t6逐渐转变为三元Al-Fe-Si或二元Fe-Al金属间化合物。奥氏体化时间为2 min时,镀层由Fe_2SiAl_7、Fe_2Al_5和FeAl_2组成;奥氏体化时间为5 min时,镀层由FeAl_2、Fe_2SiAl_2和Fe_5SiAl_4组成;奥氏体化时间为8 min时,镀层由FeAl_2和Fe5Si Al4组成。由于Fe_2SiAl_2和镀层/钢基体界面扩散层中Al原子的扩散系数远大于Fe原子,导致从镀层向钢基体晶界及晶粒内扩散并与之反应所消耗Al原子的量远大于从钢基体扩散到镀层中的Fe原子量,从钢基体中流入到镀层中的空位数量远大于从镀层中流入到钢基体中的空位数量。原子的不平衡扩散及镀层/钢基体界面空位数量的富余使得扩散反应层与镀层的交界区域形成了Kirkendall空洞。22MnB5钢奥氏体化时,热镀Al-10%Si镀层表面形成一层稳定的Al_2O_3氧化膜,镀层的高温氧化现象非常有限,热镀Al-10%Si镀层可以作为22MnB5钢热成形时的保护层。但热镀Al-10%Si镀层扩散过程中产生的脆性金属间化合物因高温塑性不足而导致镀层中产生大量垂直于镀层/钢基体界面并贯穿整个镀层的微裂纹,从而影响镀层的防护性能。
Hot stamping is an alternative technology to produce ultra-high strength steel （UHSS） with a tensile strength above 1 GPa for automotive bodies. At present, the hot-dip Al-10%Si （mass frac- tion） coating is used as a shield coating for the hot stamping steels, which protects the steels from sur- face oxidation and decarburization, and enhances their corrosion resistance. However, the microstructure evolution and compounds of hot-dip Al-10%Si coating during austenitization of 22MnB5 hot stamping steel are not clear yet. In this work, the thermo-mechanically induced microstructure evolution of hot-dip AI-10%Si coating is observed using SEM after austenitization of 22MnB5 hot stamping steel at 900 ~C for different times, and the elemental depth profiles are analyzed in hot-dip AI-10%Si coating by EDS and GD-OES. The results show that before austenitization, the hot-dip AI-10%Si coating consisted of an aluminum matrix, pure silicon, and the intermetallic compound Fe2SiAIT, which was formed by eutectic reaction, there was a thin layer, which was composed of Fe2Al5 and FeAI3 between the intermetallic compound Fe2SiAI7 and the steel substrate. When 22MnB5 hot stamping steel was austenitized at 900℃, the ternary eutectic phase AI ＋Si＋ τ6 was transformed into an AI-Fe-Si ternary intermetallic com- pound or Fe-AI binary intermetallic compound gradually in the hot-dip AI-10%Si coating. When the aus- tenitizing time was 2 min, the AI-10%Si coating was composed of the intermetallic compound Fe2SiAIT, Fe2AI, and FeAI2 phases; when the austenitizing time was 5 min, the AI-10%Si coating was composed of FeAI2, Fe2SiAI2 and FesSiAI4 phases; when the austenitizing time was 8 min, the AI-10%Si coating was composed of FeAI2 and FesSiAI, phases. Because the diffusion rate of AI atoms was much larger than that of Fe atoms in the diffusion layer of intermetallic compound Fe2SiAI2 and coating/steel substrate, the amount of AI atoms which diffused and reacted from the coating to the grain boundaries or grain of steel substr
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第11期1495-1503,共9页
Acta Metallurgica Sinica
基金
国家自然科学基金项目No.51071052
"十二五"国家科技支撑计划项目No.2012BAJ13B03~~
