| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 102 === Stainless steel 304 coated with aluminum using Hot-Dipping Alumina (HDA) method after pre-plated with Nickel to prevent mutual diffusion of iron and aluminum was investigated; and then Micro-Arc Oxidation (MAO) was performed using aluminate solution to improve the surface properties of steel.
Nickel Electroplating successfully buffered diffusion of iron atoms into the aluminum layer, preventing interfaces of materials from formation of brittle structure such as FeAl3 and Fe2Al5. During the Hot-Dipping Aluminum process, nickel reacts with aluminum to form interphases (NiAl3, Ni2Al5 and Ni3Al) which exhibit good hardness and good wear resistance.
Aluminum shows a constant reaction rate with nickel, making similar or even the same interphase layer thickness (~2μm for NiAl3 (interphase 1), ~1μm for Ni2Al5 (interphase 2) and 1μm for Ni3Al (interphase 3)) for a constant dipping-time. The reaction between Al and Ni layers begun with formation of interphase 1 and then continued by interphase 2 and for the last layer interphase 3. Along with increasing of dipping-time, nickel will scatter to all over the coating and take reaction with aluminum in form of dot-like or beam-like. For dipping-time more than 60 seconds, nickel coating of 54-60μm will disappear, leading to contact and reaction between aluminum and iron, forming Fe-Al phase. Therefore, dipping time less than 60 seconds will be the best choice for the dipping-time variable.
At last, MAO is successfully applied for Stainless Steel 304 material after being plated by nickel and dipped into the molten alumina respectively, producing aluminum oxide on the surface which enhances the surface properties of stainless steel such as hardness and corrosion resistance.
Fundamental data of MAO results in Aluminate solution and Silicate solution for Aluminum 6061 is also investigated and compared. The results shows better performance of hardness for Al2O3 in aluminate solution than those in Silicate solution. The maximum hardness of aluminate-solution is 2400HV, while that of MAO specimen using silicate solution is 1600HV.
The other comparisons of parameters such as voltage, time, etc., were investigated and discussed as well.
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