Enhancing the low cycle fatigue strength of AA6061 aluminum alloy by using the optimized combination of ECAP and precipitation hardening

In the present study, mechanical properties and low cycle fatigue behavior of a solid-solutionized AA6061 aluminum alloy produced by equal channel angular pressing (ECAP) process were investigated. The grain refinement after two passes of ECAP significantly increased the yield stress and ultimate tensile stress and decreased the ductility of the alloy. However, the improvement of low cycle fatigue strength was not as remarkable as expected. Post-ECAP aging heat treatment to the peak-aging condition imposed a notable change in the strength and ductility of the alloy so that its fatigue strength partly enhanced. An optimized combination of grain refinement and distributed fine precipitates in the matrix of the alloy was achieved by conducting aging heat treatment between passes of ECAP. The proposed procedure was proved to yield the best combination of strength and ductility, better distribution and size of precipitates, and thus a remarkable improvement in the low cycle fatigue response of the investigated material.