MECHANISM ON HETEROGENEOUS NUCLEATION OF THE PRIMARY Al PHASE ON TiAl(3) OF A HOT-DIP Zn-11%Al-3%Mg-0.2%Si COATING ON STEEL SHEET

The solidification structure of a hot-dip Zn-ll%Al-3%Mg-0.2%Si coating with a Ti addition on a steel substrate was investigated. Steel sheet was coated using a laboratory hot-dip galvanizing simulator. The coating was subsequently characterized via optical and high resolution scanning electron microscopy with EBSD and high temperature X-ray diffractometry. The hot-dip coating consisted of a combination of a Zn/Al/MgZn(2) ternary eutectic structure, primary Al phase and MgZn(2) phase. TiAl(3) acts as a heterogeneous nucleation site for Al, which was shown to have perfect lattice coherency with TiAl(3) as epitaxial Al growth from the TiAl(3) was found. The growth direction of Al is along < 110 > and has a random texture, whereas Zn has a rather strong ND// < 0001 > fiber texture.