Effect of trace Sc and Zr on the mechanical properties and microstructure of Al alloy 2618

An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was p repared by ingot metallurgy (IM) method. The aging behavior of the alloy wa s studied by Vickers hardness measurement at 200 degrees C and 300 degrees C, and the tensile properties of alloy specimens were measured at 20 degree s C, 200 degrees C, 250 degrees C and 300 degrees C. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the a ddition of Sc and Zr to 2618 alloy resulted in a primary Al-3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous cry stallization in the melt during solidification. The secondary Al-3(Sc,Zr) p articles were full coherent with matrix and had obvious precipitation harde ning effect. They also made the S' phase precipitate more homogeneous. So t he strength of alloy increases at both ambient and elevated temperatures wi thout a decrease of ductility. The ductile fracture of alloy occurs by micr ovoid nucleation, growth and coalescence, so the microvoid coalescence is t he dominant fracture mechanism.