Hot Dip Zn-6Al-3Mg-0.2Si coating steel sheet was prepared in laboratory by Hot-dip Galvanizing Simulator produced by National Engineering Lab of Advanced Coating Technology for Metal Materials. The surface and cross sectional microstructure of the samples were analyzed by using SEM and EDS. Hot dip Zn coated, 55Al-43.3Zn-1.6Si and Zn-6Al-3Mg-0.2Si coated steel sheet samples were exposed to standardized salt spray test. The Zn-6Al-3Mg-0.2Si coating and its erode production were investigated by XRD. The results showed that the hot dip Zn-6Al-3Mg-0.2Si coating had better corrosion resistance than ordinary galvanized layer.

In this paper, the influence of synthetic conditions (the molar ratio of Mg2+ and Al3+; the concentration of cationic; the aging temperature and time) on the grain size and crystallinity of Mg-Al layered double hydroxide (LDH) has been investigated systematically based on the orthogonal experiment. Mg-Al LDH was prepared using magnesite through chemical precipitation and hydrothermal methods. The samples were characterized by X-ray diffraction (XRD). The grain size which along a and c axis were calculated through Scherrer formula. The experimental results showed that the grain size along a axis increased with the rise of synthesis temperature, while the grain size along c axis reduced. It was also found that the aging temperature and time had a great influence on the crystallinity of Mg-Al LDH.

Focusing on improving the galvanizability of the third generation automotive steel, the effect of surface oxides morphologies on the galvanizability was studied. The results show that the surface oxide types of sample steels by XPS analysis after annealing in different conditions are the same, only MnO and Cr2O3 were detected and no complex oxides exist on the surface. Morphologies of surface oxides can greatly influence the galvanizability of the third generation automotive steel, nodule-like oxides surface can contribute to better wettability and inhibition layer than vitreous film-like oxides surface. Galvanizing panels of nodule-like oxides surface steels only show pinhole-sized bare spots, while panels galvanized from vitreous film-like oxide surface steels reveal larger areas of bare spots and uncoated areas. Inhibition layer observed in galvanizing panels of nodule-like oxides surface steels are compact but not homogeneous, some inhibition layer grains are fine, and others are coarse. While the inhibition layer grains of panels galvanized from vitreous film-like oxide surface steels have a non-compact morphology with some particularly fine equiaxed crystals which developed deficiently.

The electrolytic stripping technique (also known as coulometric dissolution) was a method to analysis the phase structure of galvannealed coating quantitatively, but the experimental data of electrolytic stripping cannot be used for straightforward Fe-Zn phase identification, and because quantification needs to take into account the effect of various electrochemical side-reactions. The applicability of electrolytic stripping for the phase analysis of galvannealed coatings was optimized in this article, Result show that electrolytic stripping technique can be applied to realize step-by-step dissolution of various phases species in the galvannealed coatings under the condition that the potential scanning rate was low enough, and the method allows the determination of the total Fe concentration, and the thickness and structure of the η, ζ, δ and Γ phases. Both the thickness and the various intermetallic phases content of the galvannealed coatings with different aluminum contents was characterized by the polarization curve of the electrolytic stripping technique and the proposed data analysis method, and combine the initial dissolution potential of every Fe-Zn phase in galvannealed coating.

This article describes the current quality control method during hot coating process. To improve the current quality control method during hot coating process, this article also elaborates the advanced coated product quality control system based on process analytical technology (PAT), the concept of which is “Quality by Design”, the targets of which are to enhance process stability and to improve the technological and economic index.