The Corrosion Resistance of Hard Anodised EN AW 7075 T6 Alloy

In this paper, commercially cold-rolled and artificial aged EN AW 7075 T6 alloy has been used. To ensure increased corrosion resistance, surface hardness, scratching resistance, and aesthetic features, this aluminium alloy was subsequently hard anodised and hot-water sealed (AC-A). The hard anodizing and sealing process increased surface hardness up to 304±13 HV 1 from an initial surface hardness of 194±3 HV 1. Also, the microhardness of the anodised layer and bulk material has been documented. Scanning electron microscopy (SEM) was used for microstructure and trapped precipitates investigation in the 42.9±1.4 thick formed anodised layer investigation. The T6 treated (AC) and hard anodised together with sealed (AC-A) EN AW 7075 alloy corrosion properties were evaluated using the anodic potentiodynamic polarisation tests (PPT) in a neutral 2.5% NaCl deaerated solution. The corrosion rate CR (mm/y) decreased approx. 39-times for the hard anodised and sealed EN AW 7075 alloy (AC-A), associated with the shift of the Ecorr (mV) to more positive values, degreased Icorr (µA) and increased Rp (Ohm) values compared to the artificial aged (AC) alloy. Additionally, the pitting was evaluated using laser confocal microscopy, and the pitting coefficient was also calculated.

Citric Acid as an Alternative to Sulfuric Acid for the Hard-Anodizing of AA6061

Hard-anodized is a widely used method in the aeronautical sector to improve aluminum alloys abrasion and corrosion resistance. Aim of this work was to characterize the mechanical properties and resistance hard-anodized aluminum 6061 in citric acid solution as a replacement sulfuric acid solution were investigated. Aluminum alloy 6061 was used as the base material to produce the hard anodizing; this process was carried out in a citric and sulfuric acid solution, applying current densities 3 and 4.5 A/cm2 and subsequently exposed to 3.5 wt. % NaCl solution. Microstructure and mechanical properties of the anodizing material were characterized by scanning electron microscopy (SEM) and Vickers microhardness (HV). Corrosion behavior of the hard-anodized material it was carried out with electrochemical techniques as cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) respectively. Results obtained indicated that all samples anodized in citric acid solution showed negative hysteresis and lower corrosion current density (1 × 10−10 A/cm2), indicating generalized corrosion on the material surface. EIS results show that anodizing in citric acid solution and a current density of 4.5 A/dm2 provides better corrosion protection than a sulfuric acid solution.

Dry Sliding Behavior of an Aluminum Alloy after Innovative Hard Anodizing Treatments

This work evaluates the dry sliding behavior of anodic aluminum oxides (AAO) formed during one traditional hard anodizing treatment (HA) and two golden hard anodizing treatments (named G and GP, respectively) on a EN AW-6060 aluminum alloy. Three different thicknesses of AAO layers were selected: 25, 50, and 100 μm. Prior to wear tests, microstructure and mechanical properties were determined by scanning electron microscopy (VPSEM/EDS), X-ray diffractometry, diffuse reflectance infrared Fourier transform (DRIFT-FTIR) spectroscopy, roughness, microhardness, and scratch tests. Wear tests were carried out by a pin-on-disc tribometer using a steel disc as the counterpart material. The friction coefficient was provided by the equipment. Anodized pins were weighed before and after tests to assess the wear rate. Worn surfaces were analyzed by VPSEM/EDS and DRITF-FTIR. Based on the results, the GP-treated surfaces with a thickness of 50 μm exhibit the lowest friction coefficients and wear rates. In any case, a tribofilm is observed on the wear tracks. During sliding, its detachment leads to delamination of the underlying anodic aluminum oxides and to abrasion of the aluminum substrate. Finally, the best tribological performance of G- and GP-treated surfaces may be related to the existence of a thin Ag-rich film at the coating/aluminum substrate interfaces.

Friction and Wear Response of a Hard-Anodized AA6082

The properties of anodized aluminum, and wear resistance in particular, are of high interest for the scientific community. In this study, discs of AA6082 were subjected to a peculiar hard anodizing process leading to anodized samples having different thicknesses. In order to investigate the wear mechanism of samples, unidirectional tribological tests were performed against alumina balls (corundum) under different loading conditions. Surface and microstructure of all the samples were characterized before and after the tribological tests, using different characterization techniques. The tribological tests showed remarkable differences in the friction coefficient and wear behavior of the anodized AA6082 samples, related to the microstructure modifications and to the specific applied sliding conditions.

PENGARUH VARIASI RAPAT ARUS HARD ANODIZING TERHADAP LAJU KOROSI PADA ALUMINIUM 6061

Aluminium merupakan logam yang mempunyai sifat ringan,tahan korosi, penghantar listrik dan panas yang baik serta mudah dibentuk. Meskipun tahan korosi, apabila logam Aluminium dipajang (exspose) kelingkungan ,maka akan terjadi interaksi antara logam dan terjadi korosi. Terdapat beberapa cara yang dapat digunakan untuk melindungi logam dari korosi salah satunya proses Anodisasi . Penelitian ini bertujuan untuk mengetahui pengaruh rapat arus hard anodisasi terhadap laju korosi pada aluminium 6061. Rapat arus yang di gunakan yakni 2,5 Amp/dm2, 3 Amp/dm2, dan 3,5 Amp/dm2 . setelah itu dilakukan uji kekerasan permukaan menggunakan microhardness vickers dengan pembebanan 200 gf. Nilai kekerasan dengan rapat arus 2,5 Amp/dm2 121,37 HVN, dengan nilai kekerasan 3 Amp/dm2 168,90 HVN dan 3,5 Amp/dm2 206,73 HVN. Setelah proses anodisasi , Aluminium di lakukan perendaman dengan larutan korosif NaCl (konsentrasi 3,5 %) dengan waktu perendaman 93 jam, 186 jam, 272 jam, dan 456 jam. laju korosi Aluminium 6061 yang paling tinggi berada pada waktu perendaman 279 jam untuk base material. Sedangkan nilai yang paling stabil di tunjukkan pada variasi rapat arus 3 Amp/dm2, nilai di tunjukkan tidak mengalami kenaikan yang konstan. Sementara itu untuk penggunaan rapat arus 3,5 Amp/dm2 memiliki laju korosi sedikit lebih tinggi dibanding penggunaan rapat arus 3 Amp/dm2. Kata kunci : Aluminium, Anodisasi, Laju korosi

Characterizations of Cladded 6082-T6 Aluminum Alloy Through Hard Anodizing

Aluminum alloys have attractions to be used for a wide range of applications. Although the passive film on aluminum can provide corrosion protection, it has limited wear resistance in oil and gas applications due to the aggressive environment. This work has investigated the enhancements of hard anodizing on the performance of 6082-T6 aluminum alloy surface against erosion and corrosion test environments. The study investigates the surface roughness and hardness of the hard-anodized coating before going deeper in the cross-section to study in details the macro/microstructure of the formed layer. The erosion resistance of the coated layer, in particular, the effect of sand concentration and temperature variations to the aqueous slurry impingement against material properties such as adhesion, ductility, and roughness were investigated. In addition, a series of electrochemistry tests have been conducted to verify the corrosion performance. As a reference, the un-coated aluminum substrate was instigated in all the experiments. The resulted hard anodized coating layer had good adhesion with the aluminum substrate and was consisted of two distinct amorphous sub-layers of almost 50 m thick with some elongated porosity. It has been shown that the erosion resistance of aluminum alloy can be highly improved by hard anodizing, especially at high temperature. The hard-anodized sample shows almost twice hardness values compared with aluminum substrate for both eroded and un-eroded conditions. For the corrosion behavior, the hard-anodizing coating has lower corrosion current density than the aluminum substrate.