The Effect Of Manganese On The Morphology And Performance Of Hot-dip Galvanized Coatings

Hot-dip galvanizing has been widely used in various industries due to its good corrosion resistance which could be affected by many factors, such as alloying element in zinc bath and in the substrate. This work mainly studies the effect of the alloying element manganese both in the bath and in the substrate on the growth and morphology of galvanizing coatings.It was found that much power dross deposited in the bottom of the zinc pot after adding manganese to zinc bath. The number of the power dross increases with the increase of the content of manganese in the bath. The manganese in the bath can retard the growth of the galvanizing coatings and change the coatings morphology whether aluminum is added to the zinc bath or not. The colorized surface can be seen after the samples dipped in the Zn-Mn bath. The coating consists of the compactδphase and theζphase. The manganese in the bath can promote the growth of theδphase and inhibit the growth of theζphase. The dross mainly consists of the Mn-richζphase. When dipped in the Zn-Mn-Al bath, the coatings consist of theδphase and the fragmental Mn-richδphase. Theδphase changes from fragmental to compact after manganese is added to the bath.The most common method to overcome the silicon reactivity is adding an amount of alloying elements to the zinc bath. Manganese in the zinc bath can obviously restrain the growth of the coatings. The effect of manganese in the zinc bath on the coating morphology of different substrate with the different content of silicon has been investigated. The results show that the manganese in the zinc bath has little inhibiting effect to the silicon reactivity of Q345, but has visible effect on the silicon reactivity of Q235 and Fe-0.08wt.%Si. Furthermore, manganese increases the corrosion resistance and oxidation resistance of the galvanized coatings..Manganese is one of the key alloying elements in steel, which can increase the stability of austenite. In this paper, the effect of manganese in the substrate on the galvanized coatings has also been investigated. The results show the total thickness of the coatings decreases with the increase of the content of manganese when less than 1.8wt.% of manganese has been added to the Q217 steel. The coating thickness increases with the increase of the content of manganese when more than 1.8wt.% of manganese had been added to the Q217 steel. The change of the thickness of theζ phase is consistent with that of the total thickness of the coatings. While the thickness of theδphase increases slightly with the content of the manganese in the substrates. The experimental results of Zn/(Fe-Mn) liquid-solid diffusion couple show that the total thickness of the diffusion layer increases with the increase of manganese in the substrate. The total thickness of the diffusion layer is the maximum when the content of manganese is 1.3wt.%. After that, the total thickness of the diffusion layer decreases with the increase of the content of manganese.