Kuswindayani, Nathaniela Yessa (2024) Pengaruh Perubahan Holding TIme pada Proses Retrogression and Reaging terhadap Corrosion Behavior Anoda Al-Zn-Mg pada Kapal Sepat 5 di PT Pertamina Trans Kontinental. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Kapal merupakan alat transportasi yang penting bagi negara kepulauan tetapi rentan terhadap korosi air laut. Salah satu perlindungan kapal adalah sacrificial anode dengan jenis anoda aluminium. Namun, anoda paduan aluminium rentan terhadap locallize corrosion seperti pitting corrrosion, stress corrosion cracking, dan korosi intergranular (IGC). Maka dari itu diperlukan proses retrogression and reaging (RRA) dengan tujuan meningkatkan corrosion resistance terhadap self-corrrosion dari paduan aluminium dengan pembentukan presipitat. Tujuan dari penelitian ini adalah untuk menganalisis pengaruh perubahan holding time pada proses retrogression and reaging terhadap struktur mikro dan corrosion behavior anoda korban Al-Zn-Mg. Penelitian ini dilakukan dengan cara memanaskan paduan Al-Zn-Mg pada 470oC selama 1 jam melalui proses solution heat treatment, selanjutnya dilakukan tahapan pre aging pada temperatur 120oC selama 24 jam dilanjutkan retrogression pada temperatur 180oC selama 10, 30, dan 60 menit dan tahap terakhir reaging pada temperatur 120oC selama 24 jam yang sebelum itu spesimen telah dilakukan pengujian OES. Setelah itu dilakukan pengujian consumption rate anoda menggunakan standar DnVGL-RPB401, potensiodinamic polarization, EIS (Electrochemical Impedance Spectroscopy), X-Ray Diffraction, hardness dan metalografi. Selain itu dilakukan pengujian pada media (air laut) yaitu uji pH, salinitas, dan keberadaan anion sebagai elektrolit untuk pengujian DnVGL-RPB401. Berdasarkan hasil pengujian metalografi didapatkan hasil bahwa holding time retrogression membuat jarak dan ukuran dari presipitat stabil η (MgZn2) yang lebih besar serta mengeraskan dan mendispersikan presipitat metastabil η’(MgZn2) di kisi internal atom. Semakin lama holding time pada tahap retrogression meningkatkan fraksi volume Cu yang terlarut dalam presipitat. Dimana Cu bertindak sebagai katoda dengan menaikkan potensial sel dan menginisiasi pit. Semakin bertambah waktu holding time retrogression maka menurunkan nilai consumption rate dan corrosion rate sehingga optimal pada holding time 30 menit lalu naik secara drastis dengan penambahan holding time. Ketebalan lapisan pasif (Al2O3) dapat diamati dari nilai CPEpass-T, berturut-turut urutan dari ketebalan lapisan passive dari tebal ke tipis adalah holding time 30 menit>holding time 10 menit>tanpa perlakuan>holding time 60 menit.
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Ships are an important means of transportation for archipelagic countries that are prone to seawater corrosion. One of the ship's protections is a sacrificial anode with an aluminum anode type. However, aluminum alloy anodes are susceptible to locallize corrosion such as well corrosion, stress corrosion cracking, and intergranular corrosion (IGC). Therefore, a retrogression and reaging (RRA) process is needed which aims to increase corrosion resistance to self-corrrosion of aluminum alloys by forming precipitates. The purpose of this study is to analyze the effect of holding time changes on the retrogression and reaging process on the microstructure and corrosion behavior of Al-Zn-Mg victim anode. This research was carried out by heating Al-Zn-Mg alloy at 470oC for 1 hour through a solution heat treatment process, then pre-aging stages were carried out at a temperatur of 120oC for 24 hours followed by retrogression at a temperatur of 180oC for 10, 30, and 60 minutes. and the last stage of reaging at a temperatur of 120oC for 24 hours before which the spesimen had been tested for OES. After that, the anode consumption rate test was carried out using the DnVGL-RPB401 standard, potoodinamic polarization, EIS (Electrochemical Impedance Spectroscopy), X-Ray Diffraction, hardness and metallographic. In addition, tests were carried out on the medium (seawater), namely pH, salinity, and the presence of anions as electrolytes for the DnVGL-RPB401 test. Based on the results of the metallographic test, it was obtained that the holding time retrogression made the distance and size of the stable η (MgZn2) larger and hardened and dispersed the metastable precipitate η' (MgZn2) in the atomic internal lattice. The longer the holding time in the retrogression stage will increase the fraction of the volume of Cu dissolved in precipitation. Where Cu acts as a cathode by increasing the potential of the cell and initiate pits. The more the holding time retrogression increases, it decrease the value of the consumption rate and corrosion rate so that it is optimal for the holding time of 30 minutes and then increases drastically with the addition of holding time. The thickness of the passive layer (Al2O3) can be observed from the CPEpass-T value, the sequence of the thickness of the passive layer from thick to thin is 30 minutes>holding time 10 minutes>no treatment>holding time 60 minutes.
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