Effects Of Bi, Ti, Mn On Microstructure And Properties Of Hot-dip Galvanized Coatings

In order to develop the hot-dip alloys coating with excellent properties, the Zn-xBi(x= 0.1, 0.2, 0.3, 0.4, 0.5 wt%), Zn-0.5%Al-xTi( x= 0, 0.03, 0.05, 0.07, 0.10, 0.12 wt%), Zn-5%Al-xTi( x=0, 0.03, 0.05, 0.07, 0.10, 0.12 wt%) and Zn-0.5%Al-xMn( x=0, 0.05, 0.12, 0.18, 0.25 wt%) alloy coatings were obtained by adding a trace of Al, Bi, Ti, Mn to the zinc bath and hot-dip galvanizing on the surface of Q235 steel plate. The influencing rules of Bi, Ti and Mn on the microstructure, thickness, microhardness and corrosion resistance of alloy coatings were investigated. The main research results are as fellows.Adding a trace of Bi in zinc bath can refine the grain and reduce the dross of the alloy coatings. With the increase of Bi content, the fluidity of the liquid zinc increases, the surface quality improves, the thickness of coating decreases, and the Sandelin effect is inhibited effectively, but the grain size increases, the hardness decreases, and the corrosion resistance of coating is deteriorated. The decline rate of hardness decreases with Bi content from 0.1% to 0.3%, and increases with Bi content from 0.3% to 0.5%.The Ti is added to improve the fluidity of the bath, to reduce the hot-dip galvanizing ashes, dross and zinc tumors, to improve the quality of the coating surface, to refine the grain, and the coating thickness is reduced, so Ti can inhibit Sandelin effect effectively. When the Al content is constant, the finish of coating increases firstiy and then decreases, the grain size decreases firstly and then increases, the hardness increases firstly and then decreases, the thickness decreases firstly and then increases, the corrosion rate decreases after its’ increase and then increases for Zn-0.5%Al-xTi alloy coating with the increase of Ti content. And when the Al content is constant, the finish of coating increases firstiy and then decreases, the grain size decreases firstly and then increases, the hardness increases firstly and then decreases, the thickness decreases gradually, the corrosion rate decreases firstly and then increases for Zn-5%Al-xTi alloy coating with the increase of Ti content.When the Ti content is constant, the lightness of the coating improves, coating thickness significantly increases, the grain size increases, corrosion resistance is greatly increases for Zn-Al-xTi alloy coating with the increase of the Al content. The Zn-5% Al-0.10%Ti alloy coating gets the optimal surface quality, the small grain size, the maximum surface hardness, themoderate coating thickness, the optimal corrosion resistance, and the best comprehensive performance.The moderate amount of Mn can improve the plating bath liquidity, reduce dross in the bass, refine the grain, inhibit Fe-Zn reaction, reduce the thickness of the coating, suppress Sandelin effect and improve corrosion resistance. With the increase of Mn content, the flatness of coating surface improve, the brightness of coating surface decreases, the thickness of coating decreases, the grain size decreases firstly and then increases, the hardness increases firstly and then decreases and the corrosion resistance of coating increases firstly and then decreases. The Zn-0.5%Al-0.12%Mn alloy coating gets the good surface quality, the minimum grain size, the maximum surface hardness, the moderate coating thickness, the optimal corrosion resistance, and the best comprehensive performance.