Influence of Heat Treatment on the Corrosion Resistance of Aluminum-Copper Coating

Abstract

Influence of heat treatment on the corrosion resistance of the aluminum-copper (Al-Cu) coating on the aluminum substrate was investigated. The coating was produced by the electrical discharge alloying (EDA) method. The surface and microstructure of the specimens were observed by a scanning electron microscope (SEM). The phase analysis of the composite materials by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) indicated that intermetallic compounds (i.e., CuAl2 and Cu9Al4) were formed through reactions between Al and Cu. during the EDA process. A significant increase in the hardness of the Al-Cu coating was affected by the improvement of the alloy structure. The heat treatment of materials was carried out at 400 °C or 600 °C in the air atmosphere. A corrosion test of materials was carried out by using electrochemical methods. The corrosive environment was acidic chloride solution. After heat treatment at 400 °C the mechanical properties of the Al/Cu alloy increased significantly and the oxide layer protect of the alloy surface against corrosion. However, after heat treatment at elevated temperature, i.e., 600 °C it was found that the (Al2O3)ads and (CuO)ads coatings were destroyed. The mechanical properties of the Al/Cu alloy decreased, and its surface has undergone deep electrochemical corrosion.

Influence of Laser Treatment on the Corrosion Resistance of Cr3C2-25(Ni20Cr) Cermet Coating

“…The process of hydrogen depolarization occurs in the cathode region of the potentiodynamic polarization curves. In the acid corrosion environment, the cathodic branches of the LSV curves correspond to the simplified reduction of hydrogen ions [ 21 , 22 , 23 ]: Me 0 + n H + →Me 0 + n H 2 − m e − where Me means the Cr, Ni, and other metals.…”

“…The shift of the LSV curves towards the positive potentials may indicate an increase in the corrosion resistance of the Cr 3 C 2 -25(Ni20Cr) cermet coatings, especially for the lowest laser spot speed, i.e., 600 mm/min ( Figure 10 , curve (d)). Moreover, when Al7075 was covered with Cr 3 C 2 -25(Ni20Cr) cermet coating, the anodic reaction was as follows [ 21 , 22 , 23 ]: Me 0 + 2 H + + O 2 (MeO) ads H 2 O + m e − where (MeO) ads means (Cr 2 O 3 ) ads , (NiO) ads , and other oxides. In this case, the working electrode surface was covered mainly with a layer of (Cr 2 O 3 ) ads , (NiO) ads oxides.…”

“…It seems that under these conditions, the adsorbed oxide layer can be additionally sealed by adsorption of Cl − ions [ 22 ]: (MeO) ads + Cl − + H + → (MeClOH) ads …”

“…The adsorption layer (MeClOH) ads in the acidic chloride solution weredissolved in accordance with a chemical reaction [ 21 , 22 , 23 ]: (MeClOH) ads + H + → Me n+ + Cl − + H 2 O …”

“…The potentiodynamic polarization (LSV) curves were recorded in the potential rangefrom −1000 mV to +200 mV vs. SCE(KCl), with a potential sweep of 1 mV/s. The LSV curves were used to designate the corrosion electrochemical parameters of the tested materials [ 21 , 22 , 23 ].…”