Role of Zr and Sc addition in controlling the microstructure and tensile properties of aluminum–copper based alloys

Abstract

The present work was carried out on eight alloys containing Al–2%Cu–1.5%Si–0.5%Fe–0.6%Mn-0.4%Mg–0.07%Ti, with small amounts of Zr, Sc or both. Tensile test bars were produced using low pressure die casting. All bars were solution heat-treated, followed by artificial aging. The as-cast microconstituents were determined using electron probe microanalyzer equipped with both electron dispersive x-ray and wavelength dispersive spectroscopic systems. The results show that in addition to the currently observed Fe-and Cu-based intermetallics, several Zr- and Sc-containing intermetallics were also formed during solidification (of the present alloys). Neither the Sc/Zr nor the Sc/Al ratio is constant, and both ratios may vary from one particle to another. The presence of Zr or Sc has a significant grain refining effect, equivalent to that obtained from the addition of a Ti-based grain refiner. The main influence of a Zr or Sc addition on the tensile properties of the base alloy appears during aging, and before the onset of softening. Although the addition of Zr or Sc improves the alloy tensile properties, Sc is less effective compared to Zr. Also, a Sc content beyond 0.15% results in no further improvement in the alloy strength.