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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。
The microstructure changes of hot-dip Al-10% Si (mass fraction) coating in 22Mn B5 steel at 900 ℃ for different austenitizing time were observed by SEM. The post-austenitizing heat was analyzed by EDS and GD-OES Elemental distribution of Al-10% Si plating. The results show that, before the austenitization of 22Mn B5 steel, the Al-10% Si hot-dip coating mainly consists of pure Al, pure Si and the intermetallic compound Fe_2SiAl_7 formed by eutectic reaction between the two, Thin layer of a compound layer of Fe2Al5 and FeAl_3. After austenitizing at 900 ℃, the ternary eutectic Al + Si + t6 in hot-dipped Al-10% Si coating gradually changes to ternary Al-Fe-Si or binary Fe-Al intermetallic compounds. When the austenitizing time is 2 min, the coating consists of Fe 2 SiAl 7, Fe 2 Al 5 and FeAl 2. When the austenitizing time is 5 min, the coating consists of FeAl 2, Fe 2 SiAl 2 and Fe 5 SiAl 4. When the austenitizing time is 8 min, FeAl_2 and Fe5Si Al4 composition. Since the diffusivity of Al atoms in the interfacial diffusion layer of Fe 2 SiAl 2 and the coating / steel substrate is much larger than that of Fe atoms, the amount of Al atoms consumed to diffuse and react with each other from the coating to the grain boundaries and grains of the steel substrate is much larger than that of Al atoms diffused from the steel substrate The amount of Fe atoms in the coating, the amount of vacancies that flow into the coating from the steel substrate is much greater than the amount of vacancies that flow into the steel substrate from the coating. The unbalanced diffusion of atoms and the vacancy of the interface between the coating and the steel substrate make Kirkendall voids formed in the interface between the diffusion reaction layer and the coating. When austenitizing 22MnB5 steel, a stable Al_2O_3 oxide film is formed on the surface of Al-10% Si hot-dip coating. The phenomenon of high temperature oxidation of the coating is very limited. Hot-dip Al-10% Si coating can be used as hot- The protective layer. However, brittle intermetallic compounds produced during the diffusion of hot-dipped Al-10% Si coating due to insufficient high-temperature ductility cause a large number of micro-cracks in the coating which are perpendicular to the coating / steel substrate interface and penetrate the entire coating, thereby affecting the protective performance of the coating.