HVOF-sprayed WC–CoCr coatings on Al alloy: Effect of the coating thickness on the tribological properties

A study has been conducted of the chloride-induced corrosion behavior of four different batches of galvanized steel reinforcement embedded in sound and in cracked concrete. One batch of bars was of conventionally produced hot-dipped galvanized (HDG) steel, two were prototypes of continuously galvanized rebar, and the fourth was a hot-dipped bar with an experimental Zn-Al alloy coating. Carbon (black) steel bars were also tested for comparison purposes. The continuously galvanized process is aimed at producing a thinner, but more ductile coating than that formed by conventionally hot-dipped galvanizing process. Metallographic examination of the as-received galvanized bars showed a wide variation of the coating thickness around and along the bars, and the continuously galvanized coatings were consistently thinner than specified. All bars were cast in concrete which was subsequently cracked either parallel to or perpendicular to the embedded bars. Additional specimens were tested in the sound (non-cracked) concrete. All specimens were constantly exposed to a chloride brine for 64 weeks, and were electrochemically assessed bi-weekly during the exposure period. The electrochemical results and visual examination after autopsy showed that no active corrosion was initiated in either the galvanized or black rebar reinforced non-cracked concrete specimens. Therefore, the data in this project give no indication of initiation time or chloride threshold concentration for corrosion of these bars. On the other hand, in all cracked concrete specimens, corrosion initiated at the base of the crack and extended along or around the bars. In the cracked specimens, all galvanized bars exhibited lower current densities than the black bars, with the HDG being the lowest. Recommendations are given for appropriate interpretation of half-cell potentials of the galvanized bars investigated in terms of high or low probability of active corrosion.

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Improving the tribological properties of 6061-T6 Al alloy by surface compositing with nano-size TiB2 ceramic particles via friction stir processing

International Journal of Engineering and Technology ◽

10.21817/ijet/2017/v9i1/170901402 ◽

2017 ◽

Vol 9 (1) ◽

pp. 18-23

Author(s):

Mohana Rao Ch. ◽

Mallikarjuna Rao K.

Keyword(s):

Tribological Properties ◽

Friction Stir Processing ◽

Al Alloy ◽

Ceramic Particles ◽

Friction Stir ◽

Nano Size

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Influence of micro arc oxidation coating thickness and prior shot peening on the fatigue behavior of 6061-T6 Al alloy

International Journal of Fatigue ◽

10.1016/j.ijfatigue.2019.05.013 ◽

2019 ◽

Vol 126 ◽

pp. 297-305 ◽

Cited By ~ 4

Author(s):

Y. Madhavi ◽

L. Rama Krishna ◽

N. Narasaiah

Keyword(s):

Coating Thickness ◽

Shot Peening ◽

Fatigue Behavior ◽

Al Alloy ◽

Micro Arc Oxidation

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Micro Arc Oxidation of AZ91 Magnesium Alloy – Effect of Organic Compounds in the Electrolyte

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.353.217 ◽

2014 ◽

Vol 353 ◽

pp. 217-222 ◽

Cited By ~ 1

Author(s):

Namik Kemal Gozuacik ◽

Mert Altay ◽

Murat Baydogan

Keyword(s):

Corrosion Resistance ◽

Coating Thickness ◽

Electrochemical Corrosion ◽

Organic Chemicals ◽

X Ray Diffraction ◽

Az91 Magnesium Alloy ◽

Micro Arc Oxidation ◽

Az91 Magnesium ◽

Alloy Effect ◽

Thickness Measurements

AZ91 Mg alloy was micro arc oxidized under constant electrical parameters in silicate based and phosphate based electrolytes with and without addition of organic chemicals, namely Hexamethylenetetramine (HMTA), TRIS (hydroxymethyl) aminomethane (THAM) and Glycerol in two different concentrations. Following oxidation, samples were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), coating thickness measurements, hardness measurements and electrochemical corrosion tests. Results showed that coating layers mainly consisted of MgO, Mg2SiO4 and MgF2 for silicate based electrolytes, and MgO for phosphate based electrolytes. Incorporation of organic chemicals into electrolyte composition did not change the type of the phases in the coating. However, when they are added in silicate based electrolytes, pore density and coating thickness are reduced and pore size is increased. On the other hand, there is no significant change in surface morphology when organic chemicals are added in phosphate based electrolyte. In the view point of corrosion resistance, organic chemicals did not enhance corrosion resistance of the samples oxidized in silicate based electrolytes, but exhibited some increment in corrosion resistance of the samples oxidized in phosphate based electrolytes.

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