Mechanism of Enhanced Fracture Toughness in a Novel Al-Cu-Li-Ce Alloy

The effects of different cerium contents on the mechanical properties of a novel Al-Cu-Li alloy under the peak aged conditions of T6 and T8 were studied by conventional tensile test and Kahn Tear Test. In addition, the grain boundary precipitates and fractography were observed by transmission electron microscopy (TEM) and scanning electron microscope (SEM). The results show that the UIE and the strength for alloys under T6 condition are generally lower than those for the alloys under T8 condition, while strength-toughness combination has been obtained in alloy 2#(0.15% Ce) under T8 (pre-stretched + artificially aged) condition. Meanwhile, a statistic analysis of the microscopic data by Image-Pro Plus (IPP) software, taking into account the effect of cerium content and pre-stretch was carried out. The analysis shows that the larger area fraction of the combination of dimples and intermetallic particles is corresponding to the higher value of UIE. The changes in the precipitate free zone (PFZ) width, grain boundary precipitate number density and grain boundary precipitate effective size govern the fracture resistance and the crack path of the test alloy under the conditions of the different Ce contents and heat treatment.