Creep behavior of solid solutioned and annealed Al-7075 alloy processed by equal channel angular pressing

Abstract

Effect of equal channel angular pressing ECAP process on creep properties of solid solutioned and annealed Al-7075 alloy was investigated at different temperatures and applied stresses. The microstructures of treated alloys before ECAP process were analyzed via transmission electron microscopy (TEM) and electron back scatter diffraction (EBSD). Mechanical properties of ECAPed alloy were also characterized. The fracture surface of samples was also observed by scanning electron microscopy (SEM). Subsequently, the creep mechanisms at different temperatures and stresses were discussed. The results showed that applying the initial pass of ECAP can effectively improve the mechanical properties and creep resistance of Al-7075 alloys due to impeding the dislocations movement as a result of dislocation density growth. However, applying multi passes of ECAP on annealed Al-7075 alloy did not have a positive effect on creep strength. Increasing the fraction of HAGBs and grain refinement of multi-pass annealed Al-7075 ECAPed alloy deteriorate the creep characteristic. The maximum creep rate was achieved for annealed sample after 1 pass of ECAP at 503 K under 70 MPa. Furthermore, according to different values of stress exponent, n, creep mechanism of treated samples altered. Dislocation creep as a dominant creep mechanism of annealed Al-7075 ECAPed alloy at both temperatures (503,543 K) was not altered after initial pass of ECAP; however it was replaced by grain boundary sliding after multi passes of process. Core creep mechanism of solid solutioned sample was also changed from Coble diffusion creep to viscos glide dislocation after one pass of ECAP.