Effects of crack orientation on the fatigue crack growth rate and fracture toughness of AA6063 alloy deformed by ECAP

In this study, effects of crack plane orientation on the fatigue crack growth rate and fracture toughness of 6063 aluminum alloy deformed by equal channel angular pressing (ECAP) were investigated. The ECAP process continued up to five passes without failure. Grain refinement was obvious after five passes of the ECAP process. Textural studies showed aligning the grains in known directions. After four passes, yield and ultimate strengths increase respectively from 90 MPa and 209 MPa to 300MPa and 375 MPa and also reduction in elongation was observed. The roughness decreased after the process. The fatigue crack growth rate was investigated at different load ranges with the same load ratio for different orientations. The crack growth rate increased after one pass of the ECAP process. After five passes, the AA6063 shows a lower crack growth rate in compared with as-received material. The fracture toughness of mode I and mixed-mode for different orientations were measured. The results showed that the orientation has a significant effect on the fatigue crack growth and fracture toughness of the ECAPed samples. The fracture surfaces were studied using scanning electron microscope (SEM) and refined equiaxed dimples were observed after the ECAP process.