Effects of Ni and Co on the Corrosion Resistance of Al-Si-Cu-Zn-Fe Alloys in NaCl Solution

Abstract

The corrosion behavior of Fe-containing directionally solidified (DS) and centrifugally cast (CC) Al-Si-Cu-Zn alloys with either Co or Ni additions has been investigated. Electrochemical and immersion corrosion methods were used to investigate the corrosion behavior in 0.6 M NaCl after short (1-h) and long (30-day) exposure periods. The employed solidification methods allowed the production of samples with a wide range of secondary dendrite arm spacing (SDAS) while preserving Si and Fe-containing phases. The 0.5 wt.% Ni and Co additions led to the growth of the AlFeSi(Ni) and AlFeSi(Co) phases, but no binary AlNi nor AlCo intermetallic particles have been generated. Potentiodynamic polarization studies at early exposure revealed an increase in the corrosion potential as the Ni was added for either fast or slow solidified samples. The electrochemical impedance spectroscopy at early exposure demonstrated that the Ni-modified alloy, on the other hand, was associated with smaller charge transfer resistances, indicating a reduction in the corrosion resistance after a short elapsed time into the electrolyte. However, the 30-day immersion tests revealed much lower corrosion rate of the Ni-modified alloy than the other alloys, while the corrosion rates of the Co-modified and non-modified alloys were similar. In the Ni-containing alloy, a decreased corrosion rate under a long-term corrosion process was attributed to the formation of a thick and dense alumina layer, effectively protecting the surface under such conditions. This work contributes to better knowledge of the corrosion behavior of Ni- and Co-corrected Al industrial scrap compositions.

Corrosion Behaviour of Recycled Aluminium AlSi9Cu3(Fe) Machining Chips by Hot Extrusion and Thixoforming

“…Figure 5 shows the best-fit curves with the assumed EEC (Figure 6; χ 2 < 10 −3 ), which consists of two-time constants and is often used to describe the corrosion behaviour of Al alloys subjected to plastic deformation [44][45][46].…”

“…Figure 5 shows the best-fit curves with the assumed EEC (Figure 6; χ 2 < 10 −3 ), which consists of two-time constants and is often used to describe the corrosion behaviour of Al alloys subjected to plastic deformation [44][45][46]. The proposed EEC consists of resistance elements (R) and constant phase elements (CPE) as follows: electrolyte resistance (Rel ≈ 6 Ω cm 2 ), surface layer resistance (R1), charge transfer resistance (R2), CPE of the surface layer (Q1), and CPE of the double layer (Q2).…”

Deciphering Microstructures and Phases of Gas-Atomised Novel Al-Fe-Si-Cr-Ni Alloys

“…On the other hand, Ni in aluminium alloys is known to stabilise mechanical properties at elevated temperatures due to the low diffusivity in aluminium [10]. In addition, the presence of Ni in Al-Si alloys enhanced the corrosion resistance, decreasing the pitting rate under a long-term corrosion process [11]. Despite evidence of the beneficial aspects of Cr and Ni as iron correctors in Al-Si compositions, their content in the alloy is less than 1.0 wt.%.…”