No abstract

Studies of Fe‐contaminated Al‐based scraps have drawn attention for years. However, little has been researched about the effects of cobalt (Co) and nickel (Ni) additions to contaminated scraps both under slow solidification (directional solidification, DS) and fast solidification regime (copper mold centrifugal casting, CC). As such, the current study examines a representative low‐alloy Al–Si chemistry from industrial scraps, i.e., the Al–7%Si–0.6%Fe–0.35%Cu–0.25%Zn (% by weight). This alloy is changed independently using Ni and Co. It is observed that a mixture of uneven distributed α and β Fe‐bearing particles prevails for all tested alloys and solidification conditions. The coexistence of both phases agrees with the charts proposed by Gorny's work for the range of secondary dendritic spacing, λ 2, observed. Although the Fe‐containing particles are smaller for fast‐solidified samples, they still maintain the acute morphology and, in some cases, the Chinese script shape. This results in a reduction in ductility of the order of 65% for the nonmodified and Ni‐modified samples considering mean λ 2 varying from 20 μm (DS) to 6.5 μm (CC), despite improvements in mechanical strength. Furthermore, addition of Co results in a higher number of Fe‐based particles within the microstructure. In this case, the largest particle/α‐Al interfacial area results in slightly poor ductility (~6–8%) and higher strength (175–205 MPa), with less ductility loss when DS and CC samples are compared.

No 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.

No abstract