奥氏体化过程中热冲压钢Al-Si镀层的组织演化

Microstructure evolution of Al-Si coating on hot stamping steel during austenitizing

利用差示扫描量热仪、场发射电子探针和激光共聚焦显微镜研究了22MnB5热冲压钢奥氏体化过程中Al-Si镀层的组织演化。镀层板升温过程中,Al-Si镀层在570℃左右熔化;由于温度较低,Al、Fe、Si原子的扩散受到Fe_(2) SiAl_(7)阻挡。当温度升到610℃左右时,扩散到镀层的Al原子增多,使得Fe_(2)Al_(5)进一步生长;Si原子向基体和镀层外表面扩散,由于Fe_(2)Al_(5)溶解Si原子能力弱,因此在Fe_(2)Al_(5)晶界处形成一层沉淀物FeSiAl_(2),其余的Si原子就扩散在镀层表面形成Fe_(2) SiAl_(7)。750℃时,Al原子扩散到基体中形成了Fe_(3)Al;镀层中的Fe原子增加使Fe_(2)Al_(5)和FeAl_(2)不断生长;由于Fe_(2)Al_(5)和FeAl_(2)相中Si原子的溶解度低,因此会在晶界处形成Fe_(3) SiAl_(5)沉淀物;与Fe_(2)Al_(5)、Fe_(3) SiAl_(5)、Fe_(3)Al相比,FeAl_(2)相的生长速度更快,所占Al-Si镀层整体体积最大,这是因为FeAl_(2)正交晶格中沿c轴的高空位率(30%)导致了FeAl_(2)相的生长动力学更强。

Microstructure evolution of Al-Si coating during austenitization process on the 22MnB5 hot stamping steel was studied by means of differential scanning calorimeter,field emission electron probe and laser confocal microscope.The results show that during the heating process of the coated plate,the Al-Si coating melts at about 570℃.Due to the lower temperature,the diffusion of Al,Fe,and Si atoms is blocked by Fe_(2) SiAl_(7).When the temperature rises to about 610℃,the diffusion of Al atoms into the coating increases,which makes Fe_(2)Al_(5) further grow;Si atoms diffuse to the outer surface of the coating and the substrate.Because Fe_(2)Al_(5) has a weak ability to dissolve Si atoms,a layer is formed at the Fe_(2)Al_(5) grain boundary in which precipitate is FeSiAl_(2),and the remaining Si atoms diffuse on the surface of the coating to form Fe_(2) SiAl_(7).At 750℃,Al atoms diffuse into the matrix to form Fe_(3)Al;the increase of Fe atoms in the coating makes Fe_(2)Al_(5) and FeAl_(2) continue to grow;due to the lower solubility of Si atoms in the Fe_(2)Al_(5) and FeAl_(2) phases,Fe_(3) SiAl_(5) precipitates will form at the grain boundaries.Compared with Fe_(2)Al_(5),Fe_(3) SiAl_(5),Fe_(3)Al,the growth rate of FeAl_(2) phase is faster,and it occupies the largest volume of Al-Si coating.This is because of FeAl_(2) orthorhombic crystals,the high vacancy rate(30%)along the c-axis in the grid leads to stronger growth kinetics of the FeAl_(2) phase.