基于三点弯曲试验研究合金化镀层剥落机制

通过三点弯曲试验,利用电子探针(EPMA)、扫描电镜(SEM)及金相显微镜(OM)研究了合金化镀锌板(GA)不同应力状态(压应力、拉应力)下裂纹的扩展、延伸及镀层的剥落.结果表明:锌层从合金化炉出来冷却过程中锌层中的裂纹产生于δ和Γ相中.在变形过程中,压应力和拉应力侧裂纹的扩展和锌层的剥落机制不同.在拉应力一侧,裂纹沿着垂直板面的方向延伸,到达Γ-αFe界面,沿着平行于Γ-αFe界面继续延伸,与第二条裂纹接触后,锌层剥落;在压应力一侧,裂纹沿着与板面成一定角度的方向扩展,最后镀层剥离或者在δ相内或者与拉应力一侧相同,到达Γ-αFe界面后,沿着Γ-αFe界面延伸最后产生破坏.实验结果还表明,镀层在压应力条件下更容易产生粉化现象.

Exfoliation Mechanism of Galvannealed Coating by Three Point Bend Test

The open， stretch and exfoliation of cracks in the galvannealed (GA) steel sheets under different stress states (tensile or compressive stress) were studied by three point bend test， EPMA， SEM and OM. The results showed that the cracks are generated in the δ and Γ phase during the cooling process after alloying annealed. The open， stretch and exfoliation mechanism of cracks in the coating are different for the tensile and compressive stress. When the coating subjects to tensile stress， the cracks propagate perpendicularly to coating plane， then the cracks reach and propagate along the Γ-αFe interface， while contact to the second crack， the coating exfoliates. In the coating subjected to compressive stress， the cracks are generated in the δ phase and propagated at an angle inclined to coating plane in the δ phase. Then， fracture occurs within δ phase or along the Γ-αFe interface. Furthermore， the exfoliation of the coating occurs more easily in compressive deformation than in tensile deformation.