Fused Zn-Al-based plated steel sheet and its manufacturing method

摘要

PROBLEM TO BE SOLVED: To manufacture a hot-dip Zn—Al-based plated steel sheet having a beautiful plating appearance without defects such as dross adhesion defects and having excellent plating processability. SOLUTION: A steel sheet is recrystallized and annealed, and then immersed in a molten Zn-Al plating bath containing 0.5 to 4.8% by mass of Al to perform molten Zn-Al plating. -From the start of immersion in the Al-based plating bath to the completion of solidification of the hot-dip plating metal attached to the steel sheet pulled up from the plating bath, the contact with the hot-dip plating metal and the distance from the steel sheet are 0 to 50 mm. From the ultrasonic oscillating member set to, an ultrasonic wave having an ultrasonic frequency of 10 to 120 kHz is applied to the steel sheet for 0.010 to 0.500 seconds, and cooling of the steel sheet is started within 30 seconds after the application of the ultrasonic waves is completed. Then, the steel sheet is cooled at an average cooling rate of 1.0 ° C./sec or more up to 250 ° C. [Selection diagram] Fig. 1