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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. [ABSTRACT FROM AUTHOR]

The composition of a commercial duplex stainless steel was modified with boron additions (3.5, 4.5, and 5.5 wt.%) and processed by rapid-quenching techniques: Melt-spinning, copper-mold casting, and high-velocity oxygen fuel (HVOF). Spray deposition was also used to produce alloys as the process may induce rapid-solidified-like microstructures. These processing routes led to microstructures with distinguished corrosion resistance. Among the alloys with different boron contents, the 63.5Fe25Cr7Ni4.5B composition enabled the production of fully amorphous ribbons by melt-spinning. The cooling rate experienced during copper-mold casting, high-velocity oxygen fuel, and spray deposition did not ensure complete amorphization. The crystalline phases thereby formed were (Fe,Cr)2B and (Fe,Mo)3B2 borides in an austenitic-matrix with morphology and refinement dependent of the cooling rates. Fully amorphous 63.5Fe25Cr7Ni4.5B ribbons exhibited outstanding corrosion resistance in chloride-rich alkaline and acid media with negligible corrosion current densities of about 10−8 A/cm² and a broad passivation plateau. Although the specimens of the same composition produced by HVOF process and spray deposition exhibited lower corrosion resistance because of intrinsic porosity and crystalline phases, their corrosion behaviors were superior to those of AISI 1045 steel used as substrate with the advantage to be reinforced with hard borides known to be resistant against wear. [ABSTRACT FROM AUTHOR]