Zn-Feめっき層の組成および組織制御による改質に向けたスパッタリング成膜による検証

抄録

Improvement of the powdering resistance of galvannealed (GA) coatings is a key issue in automotive GA steel sheets. To make the relationship between powdering resistance and microstructure of GA layer, sputtering fabrication process was used to prepare Zn-Fe intermetallic films with various composition and microstructure in this study. Zn-Fe films with 1500 nm in thickness were deposited on an iron substrate by RF magnetron sputtering. Г+Г₁ two-phase film (17.2~24.4 at.%Fe) was found to show a severe powdering by 3-point bending test, while Г₁ (16.2 at.%Fe) or Г (34.3 at.%Fe) single-phase films showed much better powdering resistance. These results indicate that Г/Г₁ interfaces boundaries have a low interfacial strength compared to that of Г/iron or Г₁/iron interfaces. To improve the low powdering resistance of the Г+Г₁ two-phase film, we investigated the effect of grain size refinement by B addition on the powdering resistance. It was found that the grain size refinement by B addition drastically improves the powdering resistance of Г+Г₁ two-phase film. The decrease in the fracture toughness of Г+Г₁ two-phase film by grain refinement was suggested to cause the improvement of its powdering resistance.