Fabrication And Creep Crack Growth Behavior Of Al/Al-4%Cu Graded Materials

Al/Al-4%Cu graded material was fabricated by stacking powder metallurgy processing. For comparison, the same processing was used for preparing pure Al homogeneous material and Al-4%Cu homogeneous alloy. The density of hot-pressed Al/Al-4%Cu graded material is2.6806g/cm3The creep crack growth tests of Al/Al-4%Cu graded material were performed under constant load. Results showed that the creep crack propagation process can be divided into three stages:slow crack propagation stage, steady crack propagation stage and the rapid instability crack propagation stage. When the creep crack grows to graded region, the creep crack growth rate of Al/Al-4%Cu graded material has a tendency to decline. The morphology of fracture and crack path at graded region can well explain that the graded structure can improve the performance of creep crack growth resistance.The specimens of three states were obtained, including F state (hot-pressed state), T4state (503℃solid solution treatment for6h followed by water quenching), and T6state (160℃aging for12h after T4treatment). Effects of heat treatment on the creep crack growth behavior in Al/Al-4%Cu graded material were investigated. Research shows that distribution of copper composition is more continuous and the thickness of graded layer increases, due to the Cu element diffusion in heat treatment process. For F, T4and T6state, as creep crack tip reaches the same length, crack propagation rate reduces and the steady-state duration stage extends in proper order. When F, T4and T6state of creep crack tip arrives at the graded region, retardation phenomenon occurs.The creep crack growth tests of T6state specimens were carried out under different loadings. Effects of loadings on the creep crack growth behavior in T6state specimens were investigated. It is shown that, compared with under high loading, the incubation period of T6state specimen extends obviously under low loading condition. Under low load, duration of specimen extends at a constant crack growth rate. However, effects of loadings on rapid propagation stage is not obvious. Throughout the crack propagation process, under low loading, the creep crack growth rate of T6state specimen is lower than that of under high loading. When the creep crack tip reaches graded region, the creep crack growth rate has a trend of decreasing. However, under low loading, the downward trend is more apparent. As a result, the creep crack propagation resistance performance of graded region is better. The creep fracture mechanics parameters were evaluated and for Al/Al-4%Cu graded material, description method of creep crack growth rate at steady stage was under investigation. Parameters used in present research including the stress intensity factor KI section stress σnet and modified J integral C cannot be directly associating creep crack growth rate of Al/Al-4%Cu graded material.