Effect of grain-boundary θ-Al2Cu precipitates on tensile and compressive creep properties of cast Al-Cu-Mn-Zr alloys

Tensile and compressive creep tests were performed at 300 degrees C on high-temperature Al-Cu-Mn-Zr (ACMZ) alloys with 6 wt% Cu (6Cu) and 9 wt% Cu (9Cu) to evaluate the effect on creep properties of micron-size theta-Al2Cu intergranular precipitates. For compressive creep, the increased volume fraction of theta-precipitates at grain boundaries (from -0.7% in 6Cu to -6% in 9Cu) does not affect deformation rates across the investigated stress range of 15-110 MPa, consistent with creep being controlled by submicron theta '-Al2Cu precipitates within grains, whose size and fractions are the same in both alloys. In contrast, for tensile creep, 9Cu creeps faster than 6Cu at stresses above 20 MPa, and this difference increases with the stress level. This discrepancy between tensile and compressive creep behavior is explained by cavitation during tensile creep, which is favored by higher volume fraction and larger size of intergranular theta precipitates in 9Cu. Conversely, larger precipitates impede cavity linkage resulting in improved creep ductility of 9Cu as compared to 6Cu at 300 degrees C.

Automated summary

At 300 degrees C, there is a discrepancy in the performance of 9Cu alloy in compressive and tensile creep. In tensile creep, 9Cu creeps faster at high stresses, while in compressive creep, the higher volume fraction and larger size of intergranular precipitates in 9Cu aid in cavitation formation but impede cavity linkage.