The Roles of Ni and Co in Dendritic Growth and Tensile Properties of Fe‐Containing Al–Si–Cu–Zn Scraps under Slow and Fast Solidification Cooling

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.