Study On The Microstructure And Corrosion Resistance Of Spray Forming Zn-Al-Cu Alloy

In this paper, the microstructure and corrosion behavior of spray formed Zn-Al-Cu alloy were studied. The morphology, type and distribution of different phases in the microstructure were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). The effect of copper content and fabrication method on the microstructure was also discussed. The corrosion behavior and corrosion mechanism of spray formed Zn-Al-Cu alloy were studied by means of corrosion tests, optical microscopy(OM), X-ray diffraction(XRD) and scanning electron microscopy(SEM), and the relationship between copper contents, temperature, corrosion medium and corrosion resistance was analyzed.The results indicate that the primary microstructure is composed of the aluminum-rich a' phase, the zinc-richβphase and the well-formed eutectoidα+ηlamellae or irregularly complex structures throughβdecomposition, the grains were equiaxed with an average size of 20～30μm, the aluminum-richα' phase was unstable, some of which decomposed very small lamella structuresα+η.The solution of copper in the matrix was improved by spray forming technology, There was no precipitation of CuZn5 in the spray-formed Zn-30Al-1Cu alloy, while a small amount of CuZn5 phases with very small size were observed in Zn-30Al-2Cu and Zn-30Al-4Cu alloy.The natural corrosion potential and self-corrosion current density were tested by the mean of tafel equation, with the increasing of copper content, self-corrosion potential was almost same while the self-corrosion decreased first then increased. The open circuit potential, the natural corrosion potential and self-corrosion current density of Zn-30Al-1Cu alloy varied with temperature, while the open circuit potential was decreased, both natural corrosion potential and self-corrosion current density were increased. The pitting corrosion was not found in the Zn-Al-Cu alloys.In salt spray corrosion medium of 35℃, the corrosion reason of spray formed Zn-30Al alloy was the dissolution of zinc-richηphase firstly, then the a phase in the grain boundary also dissolved which made the corrosion became intergranular corrosion. With the increasing of copper content, the corrosion of rate first declined then increased. In the medium of boil water, the a phase was as anode polar, theηphase as cathode. The corrosion mechanism of spray formed Zn-30Al alloy were intergranular corrosion and inter-phase corrosion, the driving force of corrosion was the potential difference. With the addition of copper, the corrosion rate of spray forming Zn-30Al alloy was decreased, and the corrosion rate of spray formed Zn-30Al-1Cu alloy was smaller than the other experimental alloys.