Effect of Sc content on microstructure and properties of Al-Zn-Mg-Cu-Zr alloy

The effect of Sc content on microstructure and properties of Al-Zn-Mg-Cu-Zr alloy was studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), tensile tests, hardness measurements and corrosion evaluation. It is revealed that the increase in the volume fraction of the η' phase and the precipitation of Al3(Sc, Zr) particles within the alloy contribute to the significant grain refinement within the Al-7.0Zn-3.0 Mg-0.3Cu-0.15Sc-0.12 Zr (wt.%) alloy. The strength and hardness of the alloy have also been improved. Due to the addition of Sc element, the precipitates at the grain boundaries of the alloy become discontinuous, and the size of such precipitates is reduced. The population density is also decreased. Consequently, the alloy has excellent resistance to intergranular corrosion and exfoliation corrosion. Electrochemical data also shows that the alloys have a smaller tendency to corrode and slower corrosion rates.