Method for plating surface of steel with Al-Zn-Mg-Si alloy plating layer in continuous hot-dipping manner

The invention relates to a method for plating the surface of steel with an Al-Zn-Mg-Si alloy plating layer in a continuous hot-dipping manner and a manufacturing process of the Al-Zn-Mg-Si alloy plating layer. The Al-Zn-Mg-Si alloy plating layer manufactured through the process comprises, by weight percentage, 48% to 55% of Al, 40% to 50% of Zn, 1% to 4% of Mg and 1% to 3% of Si. The manufacturing process of the Al-Zn-Mg-Si alloy plating layer includes the steps of firstly, surface cleaning treatment, secondly, reducing and annealing, thirdly, hot-dipping plating in plating liquid at the temperature from 550 DEG C to 700 DEG C, fourthly, the annealing process for 0.1 s to 5 s at the temperature from 400 DEG C to 700 DEG C and air cutter leveling and fifthly, cooling. The manufactured alloy plating layer contains Al-rich dendritic crystal phases, Zn-rich interdendritic phases, Mg2Si phases and a small amount of MgZn2 phases. The preferable alloy components can guarantee the even plating liquid components, floating residues are few, and the quality of the plating layer manufactured through the continuous hot-dipping process is uniform and stable. The content of the Mg2Si phases on the surface of the plating layer can be increased through the annealing process performed after dipping plating is performed, and the corrosion resistance of the plating layer is improved.