Research on design and microstructure of hot-dip Zn-Al-Mg/Sn alloy

In this paper, based on the effect of different intermetallic compounds on liquid metal induced embrittlement (LMIE) and corrosion resistance of GI coating during hot-forming process, a low-aluminum, low-magnesium Zn-Al-Mg alloy with high corrosion resistance is designed by CALPHAD method. The equilibrium phase diagram and solidification path of Zn-Al-Mg(-Sn) zinc-rich corner are calculated, and the phase composition of the alloy is predicted and verified by experiments. The results show that the calculation results based on the CALPHAD method are highly reliable and can provide guidance for material design. The Mg-Zn phase in the melted Zn-Al-Mg alloy is Mg2Zn11, which is different from the MgZn2 phase in the traditional industrial field. This difference may be attributed to the difference of alloy element content and cooling rate. After the Sn is added on the basis of Zn-Al-Mg, hcp-Zn phase is initially precipitated in the alloy, then fcc-Al and Mg2Zn11 phases are precipitated at the same time, and then hcp-Zn + fcc-Al + Mg2Zn11 + Mg2Sn phase coexists. Finally, the phase is transformed into hcp-Zn + fcc-Al + Mg2Sn ternary eutectic. In addition, the corrosion resistance of the designed alloy shows that the Mg2Zn11 phase in eutectic structure can improve the corrosion resistance, while the improvement of the corrosion resistance of Mg2Sn is weaker than the Mg2Zn11 phase.