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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.

Portland cement has become an essential building material in the last century. Its production unfortunately leads to noticeable CO2-emissions. The development of Belite-Yeelimite-Ferrite (BYF) cement as alternative binder is a promising solution with a decrease of 20-30% in CO2 emissions. One important issue for this new cement is its ability to passivate mild steel. Only few results about it are currently available due to the relatively new nature of the technology. This paper discusses the electrochemical behavior of steel in a BYF matrix. The impact of chloride (present in raw materials as permissible impurities) was considered too. An ordinary Portland cement was used as reference. Mortar specimens with embedded steel rebar were cast with varying chloride contents (0.0, 0.2, 0.4 and 1.0% of chloride by mass of cement). Electrochemical techniques such as half-cell readings, linear polarization resistance (LPR) and large potentiodynamic polarizations were carried out. Specimens contaminated by chloride up to 0.4% showed low corrosion rate (< 1 μm/year) during the first year of measurements. High corrosion activity (>5 μm/year) was yet observed with a chloride content of 1.0% by mass of cement. Therefore steel embedded in BYF mortar passivates and a chloride content up to 0.4% by mass of cement can be tolerated. The contamination by 1% of chloride by mass of cement (not allowed for reinforced concrete made with Portland cement according to the European standard EN 206) leads to active corrosion.