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A method combining crystal plasticity (CP), the eXtended Finite Element Method (XFEM), and cohesive zone model (CZM) with traction separation law is developed for an Al-Cu-Mg alloy to predict the effect of grain orientation on fatigue crack propagation (FCP) during stage ΙΙ within a single crystal. The simulation results show that of all the orientations, Goss grain possesses the largest fatigue crack deflection, then followed by Cube orientation. Comparatively, Brass, Copper, S and Random grains have relatively small crack deflection angles. Besides, it is found that Goss grain with the largest fatigue crack deflection possesses the lowest FCP rate as compared with other orientations. The results of simulations are consistent with previous experimental observations. This indicates that this coupled CP XFEM CZM simulation method is capable of well predicting the effect of grain orientation on FCP during fatigue stage ΙΙ of Al-Cu-Mg single crystal.

Stress formation of monocrystals and bicrystals is investigated in specific oriented grains and grain boundaries of AA2024 alloy by using Crystal Plasticity Finite Element Method (CPFEM). The simulations show that the maximum Schmid factor (SF) value and the number of equivalent initial slip system (EISS) play a principal role in controlling the magnitude of internal stress within monocrystals. For bicrystal model, Goss and Cube grains are not the best ones for relieving stress concentration caused by their orientations, but they are the best ones for relieving grain boundary (GB) stress concentration. To this end, the dependence relations are discussed between GB stress and an advanced comprehensive factor combining SF, and geometry compatibility factor for 5 independent slip systems. It is found that this proposed comprehensive factor considering the contribution from 5 to independent slip systems effectively improves its dependence on GB stress.

Effects of the trace element germanium (Ge) on the quench sensitivity of an Al-Zn-Mg-Zr alloy were investigated in the present work. The results showed that the Ge-bearing alloy exhibited lower quench sensitivity as compared to the Ge-free alloy. This phenomenon could be reasonably interpreted in terms of the stability of supersaturated solid solution of alloys after quenching from an elevated temperature. The apparent vacancy formation energies for the Ge-free and Ge-bearing alloys were determined to be 0.49 and 0.58 eV respectively. This suggested that the addition of a small amount of Ge was able to trap excess vacancies, leading to a decrease in the amount of coarse dispersoids and resultant low quench sensitivity in Ge-bearing alloys. Therefore, Ge could be used in alloy productions, which require a slow cooling rate to reduce the residual stresses and distortions. [ABSTRACT FROM AUTHOR]