Abstract
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.
Highlights
Aluminum and its alloys have been widely used in many industries due to their low density, lightweight, high thermal and electrical conductivities, and specific strength.the low hardness and poor wear resistance of these materials limit their application range to parts serving only in the absence of friction [1,2].It is well known that surface modification enhances the tribological properties of metal alloys [3,4,5,6,7,8]
All AAO layers show the typical microstructure of anodic aluminum oxides with very fine-scale and Ag-rich dendrites that appear only at the coating/aluminum substrate interfaces of G- and GP-treated surfaces
In agreement with the phase compositions analysis, all AAO layers exhibit amorphous structures with some boehmite deriving from the sealing in hot deionized water; The hard anodizing treatment (HA) treatment generates the hardest anodic aluminum oxides, while GP produces the softest
Summary
Aluminum and its alloys have been widely used in many industries due to their low density, lightweight, high thermal and electrical conductivities, and specific strength.the low hardness and poor wear resistance of these materials limit their application range to parts serving only in the absence of friction [1,2].It is well known that surface modification enhances the tribological properties of metal alloys [3,4,5,6,7,8]. Aluminum and its alloys have been widely used in many industries due to their low density, lightweight, high thermal and electrical conductivities, and specific strength. With respect to aluminum and its alloys, the use of processes such as conventional and hard anodizing [9], thermal spraying [10], and plasma electrolytic oxidation [11] allows overcoming issues concerning their insufficient friction properties. The aluminum alloys 6xxx series are becoming increasingly important in the aerospace and automotive industries due to their suitable physical properties such as weldability and formability coupled with the low cost. Anodizing is usually employed as an engineering solution for improving the tribological behavior of these aluminum alloys [2]
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