| 摘要 |
A surface treatment process for hot dip zinc-iron alloy coated steel sheets comprises applying a chromium (alloy) thin film of NOTGREATER 1 mu m thickness onto the alloy coating and then cold working under conditions which maintain an arithmetic mean surface roughness (Ra) of greater than 0.2 mu m. Preferably, the thin film is applied by vacuum deposition and the work hardening operation produces 0.5-4% elongation. Also claimed is a method of resistance welding a hot dip zinc-iron alloy coated steel sheet in which, prior to the actual welding operation, the sheet is surface treated as described above. Further claimed is an alloy-galvanised steel sheet which has the chromium (alloy) thin film by the above surface treatment process. The film is discontinuous and distributed in the valleys of the sheet surface roughness. |
