Research On The Corrosion Resistance And Mechanical Properties Of Hot DIP Aluminized Ductile Cast Iron

The corrosion resistance of ductile cast iron in atmosphere, seawater and soil is poor although it has advantages such as good damping property, machining performance and low price. Hot-dip aluminizing can improve the high temperature antioxidant and corrosion resistance properties of iron and steel workpieces, and is widely used in fields such as petroleum, chemical industry, metallurgy and machinery. The effect of molten aluminum of different composition on the growth law, corrosion resistance and mechanical properties of hot dip aluminized ductile iron is investigated in this study, as well as the corrosion mechanism and fracture failure mechanism.Aluminized coating consists of Al layer and Fe-Al alloy layer, the growth of alloy layer is controlled by reaction-diffusion and follows the parabolic law approximately. The alloy layer is thick and has a tongue-like interface between alloy layer and matrix when hot dipped in Al and Al-1.0RE. The alloy layer is thinner with a relatively regular interface when hot dipped in Al-3.6Si and Al-3.7Si-1.0RE.The process of corrosion can be divided into four phases:formation of passive film, initiation of pitting, growth of pitting and destruction of passive film. When RE is added into the molten aluminum, the aluminum will be purified, defects in the passive film will decrease and the initiation of pitting will be prevented, so that corrosion resistance of hot dip aluminized ductile iron can be improved.The strength and ductility of ductile cast iron significantly decrease when hot dipped in Al and A1-1.0RE, and it is nearly the same to the annealed ductile cast iron when hot dipped in Al-3.6Si and Al-3.7Si-1.0RE with the specimen thickness of5mm, while the strength and ductility of ductile cast iron decrease to varying degrees when hot dipped in molten aluminum of different composition with the specimen thickness of1mm.When alloy layer is thick with a tongue-like interface, principal crack can be noticed in the alloy layer, and a large amount of microcracks in the ferrite between principal crack and graphite come into being because of stress concentration, the increase of microcrack density leads to principal crack growing and matrix being torn. When alloy layer is thin and the interface between alloy layer and matrix is regular, part of alloy layer will be divorced from matrix because of the continuous crack in the alloy layer, thus the failure mechanism is similar with the annealed ductile cast iron.