Objective of this study is to find a way to control the generation of bright pitting defects on the surface of hot-rolled galvalume steel sheets produced using the United States Corp method. In our study, Scanning Electron Microscope (SEM) and Energy Disperse Spectroscopy (EDS) were used to analyze the microscopic characteristics and components of the said defects, and it's found that the cause of Type-I pitting defects is the dross residuals in the zinc kettle that are adhered to the surface of the strip steel caused by improper setting of the air-knife blowing process; and the cause of Type-Ⅱ pitting defects is the suspended particles or intermediate alloy particles entering the coating layer from the zinc kettle. Methods such as strictly controlling the compositions of aluminum-zinc ingots, adjusting the parameters of the air knife during the production process, regularly picking up bottom dross and irregularly picking up surface dross remaining in the equipment, and regularly cleaning the equipment could be taken to tighten the monitoring and management of dross in the kettle, ensure the purity of the plating solution, and effectively solve the bright pitting defects. This study provides a guidance for steel sheet manufactures to improve their manufacturing techniques and control the production process.

In accordance with the requirements of hot-rolled aluminum-zinc plating and cold-rolled aluminum-zinc plating mixed line for producing construction steel and the production process characteristics of hot-dip aluminum-zinc products, the critical process control points are put forward by combining theoretical analysis with experimental verification. We should select proper raw materials, ensure the cleanliness of strip steel surface, strictly control the annealing temperature, the temperature of the strip steel entering the zinc pan, the temperature and composition of the plating bath, and explore reasonable and feasible process parameters such as air knife and cooling after plating, so as to produce qualified products. This study is of great significance for the improvement and process control of hot-rolled aluminum-zinc plating plates in steel plate production enterprises.