Study the Effect of Aluminum Variation on Hardness & Aluminum Loss in Zn-Al Alloy
The objective of this research is to study the hardness &aluminiumloss with percentage variation in Aluminium content added to zinc. As there is a method for coating known as Galfan is available, in which combination of 95%zinc and 5% Aluminium is used for protecting steel from corrosion.As there are not much details available about why this composition is used Zinc-5%Al, we are interested in study of effects of different composition of Aluminum with Zinc, so we study the effect by adding different composition 2.5%,4.5%,6.5%,8.5% & 11.5% Aluminum in Zinc, for this study we are using hot dip galvanizing process for studying this coating. Hot-dip galvanizing is widely used to improve the corrosion resistance of steel. To obtain high-quality coatings, some alloy elements are added to the zinc bath. Aluminum is one of the most important elements in galvanizing.Fe-Al phase diagram indicated thatα Fe is obtained between 1 to 11% of AluminiumGalfan alloy consist of 95% Zn and 5% Al. It was decided to study the effect of variation in Al content in ZincAluminium alloy .Also during melting of this alloy we wanted to observed loss of Al due to oxidation hence the above compositions were decided.
The lifetime assessment of hot-dip 5% Al–Zn coatings in chloride environments
Abstract Batch-type hot-dip zinc and 5% Al–Zn coatings were investigated for comparison of their corrosion resistance, electrochemical behavior and microstructures. The 5% Al–Zn coatings possess prominent electrochemical passivation behavior. Intermetallics formed mainly between iron, aluminum and zinc adhering to the substrate were identified with energy-dispersive X-ray analysis and are believed to be responsible for the passivation phenomena observed in the electrochemical polarization. The 5% Al–Zn coatings exhibit much better corrosion resistance than the conventional hot-dip galvanizing steels under salt spray tests. Although the corrosion potential of both coatings increases toward the noble potential as the immersion time increases, 5% Al–Zn coatings are always nobler than hot-dip zinc coatings.
Corrosion resistance of Zn-Al alloy coated steels investigated using electrochemical impedance spectroscopy
Electrochemical impedance spectroscopy and electron microscopy are used to study corrosion processes affecting hot dipped Zn-Al alloy coated steels in aerated aqueous sodium chloride. Coatings containing 4.3 and 55 wt-%Al are allowed to corrode freely at pH 3, 6, and 9 for periods of 24 h. Scanning electron micrographs of corroded samples show pitting in the 4.3%Al coating, and areas of localised dezincification and porosity development in the 55%Al coating. Electrochemical impedance spectra for the 4.3%Al coating vary little with time and pH and are consistent with oxygen transport to the corroding surface occurring by semi-infinite diffusion through solution. Similar results are found for the 55%Al coating at pH 6, where dezincification is limited. At pH 3 and 9 dezincification of the 55%Al coating is more extensive, and the impedance spectra show marked, time dependent increases in diffusional impedance contributions. It is proposed that these changes result from a progressive increase in the length and tortuosity of oxygen diffusion paths accompanying pore development as dezincification proceeds.