Effect of La on intermetallic layer of galvalume

The effect of various La levels on the reaction between pure iron panel and 55%Al-Zn-1.6 wt-%Si liquid baths during hot dipping at 600 degrees C was investigated in this work. Three bath compositions containing 0, 0.2 and 0.5 wt-%La respectively, combined with six immersion times of 10, 60, 120, 180, 300 and 600 s, were studied. It was found that La can effectively control the formation of intermetallic layer by the synergistic effect with Si. The addition of La makes Si enriched in the intermetallic layer during the hot dipping. It hinders the formation of the Fe2Al5 phase and promotes the growth of the tau(5) phase. The intermetallic layer becomes more compact and uniform after the La was added. The intermetallic layer is composed of Fe2Al5 (tau(1)/tau(9)), FeAl3 and tau(5) phase. The diffusion path model was introduced to interpret the effect mechanism of La and Si in this work.