Yu Xinxiang

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

Abstract 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.

Microstructure Evolution of Novel Al-Cu-Li-Ce Alloys during Homogenization

Abstract The present work is aimed to clarify the formation of the τ 1 (Al 8 Cu 4 Ce) phase and its formation mechanism in the high Cu content alloys with Ce addition, i.e high Cu/Li Al-Cu-Li-Ce alloys. The microstructure evolution of the alloy during the two-step homogenization annealing process was investigated. Results show that the coarse Ag+Mg enriched T B (Al 7 Cu 4 Li) phase and the primary AlCuCe phase occur under solidification. Two types of the minor τ 1 phases are formed after homogenization. It is concluded that the τ 1 phase nucleation mechanism could involve either nucleation on an existing T B phase by Ce diffusion from the Al matrix or the transformation of the primary AlCuCe phase into the τ 1 phase by Ce diffusion through the coarse primary AlCuCe phase shrink. It is deduced that the grain refinement is attributed to the primary AlCuCe, which can promote α (Al) nucleation and further prohibit the grain growth for the experimental alloy.

Effects of Cerium and Zirconium Microalloying Addition on the Microstructures and Tensile Properties of Novel Al-Cu-Li Alloys

Abstract Effects of Ce and Zr additions (combinative addition and single addition) on the microstructures and tensile properties of novel Al-5.8wt%Cu-1.3wt%Li alloys with an elevated Cu/Li ratio were investigated comparatively by a microscopy method and tensile test. The microstructural observation shows that the intermetallic dispersoid in the case of combinative addition of Ce and Zr is more significantly refined from coarse polygonal shape to fine irregular particles compared to that in the case of single addition of Ce or Zr. Due to the refinement and the modification of intermetallic dispersoid, the corresponding fracture mode changes from brittle intergranular fracture to ductile transgranular fracture during tension. In addition, microstructural analysis reveals that the addition of Ce promotes the precipitation of the T1 phase which is the predominant strengthening phase in Al-Cu-Li alloy. In comparison to Ce containing Al-Cu-Li alloy, Ce+Zr-containing Al-Cu-Li alloy raises the degree of supersaturation of Cu in matrix due to less Cu atoms being trapped in finer AlCuCe dispersoid after solution treatment. Thus it is found that the ultimate tensile strength (UTS) and yield strength (YS) for the later alloy are increased by 19.6% and 16.1%, respectively. And the elongation (El) is similar, owing to decreasing of the phase size, changing of precipitation type to T1 phase only and further grain refinement.

Effects of Cerium Addition on Solidification Behaviour and Intermetallic Structure of Novel Al–Cu–Li Alloys

Abstract The microstructure evolutions of novel Al-Cu-Li alloys with rare earth cerium (Ce) additions (0, 0.1, 0.3, and 0.5, wt%) were investigated. The as-cast samples were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction meter and electron probe microanalysis with wavelength dispersive spectroscopic. The microstructural observation shows that the grains are significantly refined with increasing the addition of Ce. Mg+Ag-rich Al 7 Cu 4 Li intermetallic phase can be observed in all experimental alloys except for the one with addition of 0.5wt%Ce, which an extra gray CuSi(AgMg) phase emerges. Furthermore, the coarse rodlike Al 2 CuLi phase is completely absent upon Ce level up to 0.3wt%. The analysis shows that the Ce addition introduces changes in the precipitation sequence and consequently in the solidification behavior of the alloy. It is deduced that the grain refinement is mainly the result of the primary Al 8 Cu 4 Ce promoting α (Al) nucleation and further prohibiting the grain growth for the experimental alloys with cerium addition.