Abstract
The rapid solidification of Al-12 Zn-3 Mg-1.5 Cu (in mass%) alloy was investigated in order to determine structure changes and the effect of Zr or Sc+Zr additions. Rapidly solidified ribbons with the thickness of 30–50 μm were obtained by a melt spinning technique. The alloys cast into a copper mould were used as a reference material. The mould cast alloys as well as the melt spun ribbons revealed the dendritic microstructure of α(Al) solid solution and η (MgZn2) phase in the interdendritic areas. Additionally the T-Mg32(Zn, Al)49 phase with icosahedral quasicrystalline symmetry was found in the form of small particles located mainly at the wheel side in the Zr or Zr+Sc containing ribbons. The refinement of the microstructure and the reduction of volume fraction of the η phase was observed in the ribbons. Large Al3Zr primary precipitates were observed in the mould cast alloy containing zirconium, while almost whole Zr in the ribbons dissolved in the aluminium solid solution. Annealing of ribbons at 400°C led to the precipitation of spherical L12-Al3Zr or Al3(Sc, Zr) particles, coherent with the matrix. They could be responsible for the improvement of properties of the aluminium alloys by the retardation of recrystallization and grain growth. Plate like precipitates of metastable η′ phase appeared after ageing at 120°C and led to the increase of microhardness up to about 230 HV.
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