PURPOSE: To form a Zn-Cr alloy plating layer excellent in phosphating property as well as in rust-preventing effect by incorporating Cr to a plating layer while changing Cr content in a thickness direction into a specific state at the time of vapor-depositing a Zn-Cr alloy plating layer onto the surface of a steel sheet.
CONSTITUTION: While moving a steel sheet in the direction of an arrow in a vacuum tank, vapor deposition is carried out by using a Cr-containing crucible 2a, as an evaporation source, located in the position on the upstream side in the direction of advance of the steel sheet under the steel sheet and also using a Zn-containing crucible 2b located in the position on the downstream side as an evaporation source, while lapping the vapors of Cr and Zn from respective crucibles. By the above procedure, a Zn-Cr plating layer in which the outermost layer part is composed of a galvanizing layer of ≥5%, preferably 0%, Cr content and Cr content at the depth of the plating layer is regulated to 5-80% and, further, Cr content is continuously increased from the surface layer toward the depth is applied to the surface of the steel sheet. By this method, the Zn-Cr alloy plating layer where the surface layer part is reduced in Cr content and excellent in phosphating property and the deep layer part is increased in Cr content and excellent in rust-preventing property can be formed.
KAWAFUKU JIYUNJI
KATO ATSUSHI
IKEDA TSUGUMOTO
IRIE KOJI
| JPH01111864A | 1989-04-28 | |||
| JPS62136562A | 1987-06-19 |