Effect of Al–15Zr master alloy on the microstructure and tensile properties of extruded Sc-free 7042 Al alloy

The purpose of this investigation is replacing precious scandium element with zirconium in Al-7042 alloy to obtain similar properties. Therefore, different amounts of zirconium (0.01-0.5%) were added to the alloy and structure and properties was studied. Scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction (XRD) were applied for this purpose. Results showed that the structures of Zr-refined samples show finer grains and a better distribution of the second phases in comparison with un-refined alloy. Significant improvement in mechanical properties was obtained with the addition of 0.3 wt.% Zr grain refiner. After T6 heat treatment, the average tensile strength, increased from 519 MPa to 741 MPa for Zr refined alloy. Microstructure analysis revealed S, T and ZrAl3 intermetallic phases in the Al–Zn–Mg–Cu system. Study of fracture surfaces showed that in small amounts of Zr, due to presence of dimples next to grains surfaces, the fracture mode is a combination of ductile and brittle. At higher Zr content the fracture mode was completely ductile with more fine dimples

Keywords:

Aluminium alloys , Grain refinement , Mechanical properties , Casting , Microstructure