Effect of Microstructure on the Corrosion Resistance of TIG Welded 1579 Alloy

The paper studies microstructure, chemical composition and corrosion activity of the tungsten inert gas welded joint of the Al-Mg-Sc alloy. An intensive corrosion attack of the heat affected zone (HAZ) was found due to precipitation of secondary phases at recrystallized grain boundaries. The ccorrosion process initiated along the boundary of α-Al grains, where a high concentration of anodic (Mg2Si and Mg2Al3) and cathodic phases ((MnFe)Al6) was observed. Increased temperatures during welding led to coalescence of the anodic phases in HAZ. Additionally, HAZ was found to be enriched with hard intermetallic compounds (Mg2Si and (MnFe)Al6). This area had a higher microhardness (930 MPa) compared to base metal (BM, 895 MPa) and fusion zone (FZ, 810 MPa). The volume fraction of secondary phases was 26% in BM, 28% in FZ and 38% in HAZ. The average grain size increased in the following order: (9 ± 3) µm (BM) < (16 ± 3) µm (HAZ) < (21 ± 5) µm (FZ). A plasma electrolytic oxidation (PEO) coating of aluminum-based material was applied to protect the weld from oxidation. The PEO-coating provided a high corrosion protection in the aggressive Cl−-containing environment

Corrosion of the Welded Aluminium Alloy in 0.5 M NaCl Solution. Part 1: Specificity of Development

This work consists of two parts. In the first part, the kinetics and mechanism of corrosion on the surface of the welded joint area of the aircraft 1579 aluminium alloy have been studied using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique) in 0.5 M NaCl. The results have revealed the corrosion process development within the weld interface due to the presence of microdefects in the morphological structure. Features of the 1579 Al alloy corrosion have also been investigated through immersion experiments, quantitative analysis of dissolved alloying elements by means of atomic absorption spectroscopy, and corrosion products characterization using XRD (X-ray diffraction) analysis. The presence of Mg as an alloying element in the 1579 Al alloy sufficiently increases the bulk pH values as a result of the intensive dissolution of Mg. These factors accelerate the corrosion activity of the studied material in the 0.5 M NaCl solution. Corrosion evolution analysis of the 1579 Al alloy sample showed the importance of the coating formation to protect this alloy against corrosion and to increase the stability of this system in the corrosive media

Corrosion of the Welded Aluminium Alloy in 0.5 M NaCl Solution. Part 2: Coating Protection

The high electrochemical activity of the aircraft 1579 aluminium alloy with a welded joint and the necessity of the coating formation to protect this material against corrosion as well as to increase the stability of the weld interface in the corrosive medium has been previously established. In this work, two suggested methods of protective coating formation based on plasma electrolytic oxidation (PEO) in tartrate-fluoride electrolyte significantly increased the protective properties of the welded joint area of the 1579 Al alloy. The electrochemical properties of the formed surface layers have been investigated using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique), EIS (electrochemical impedance spectroscopy), OCP (open circuit potential), and PDP (potentiodynamic polarization) in 0.5 M NaCl. The less expressed character of the local electrochemical processes on the welded 1579 Al alloy with the composite coating in comparison with the base PEO-layer has been established. Polymer-containing coatings obtained using superdispersed polytetrafluoroethylene (SPTFE) treatment are characterized by the best possible protective properties and prevent the material from corrosion destruction. Single SPTFE treatment enables one to increase PEO-layer protection by 5.5 times. The results of this study indicate that SVET and SIET are promising to characterize and to compare corrosion behaviour of coated and uncoated samples with a welded joint in chloride-containing media

Icephobic Performance of Combined Fluorine-Containing Composite Layers on Al-Mg-Mn–Si Alloy Surface

This paper presents the results of an evaluation of anti-icing properties of samples obtained by plasma electrolytic oxidation (PEO) with a subsequent application of superdispersed polytetrafluoroethylene (SPTFE) and polyvinylidenefluoride (PVDF). A combined treatment of the samples with SPTFE and PVDF is also presented. It is revealed that impregnation of a PEO layer with fluoropolymer materials leads to a significant increase in surface relief uniformity. Combined PVDF–SPFTE layers with a ratio of PVDF to SPTFE of 1:4 reveal the best electrochemical characteristics, hydrophobicity and icephobic properties among all of the studied samples. It is shown that the decrease in corrosion current density Ic for PVDF–SPFTE coatings is higher by more than five orders of magnitude in comparison with uncoated aluminum alloy. The contact angle for PVDF–SPFTE coatings attain 160.5°, which allows us to classify the coating as superhydrophobic with promising anti-icing performance. A treatment of a PEO layer with PVDF–SPFTE leads to a decrease in ice adhesion strength by 22.1 times compared to an untreated PEO coating