Strain‐Induced Dissolution and Precipitation of Secondary Phases and Synergetic Stengthening Mechanisms of Al–Zn–Mg–Cu Alloy during ECAP

Abstract

The evolution of secondary phase of 7A60 aluminum alloy before and after equal channel angular pressing (ECAP) deformation and the resultant variation of mechanical properties are studied by means of X‐ray diffractometer (XRD), transmission electron microscopy (TEM), optical microscope (OM), and Instron testing machine. The results show that grains are refined to submicron level after ECAP (from 9.86 µm to about 1 µm). As the strain increases, the main secondary phase (MgZn2) dissolves into the aluminum matrix to form a supersaturated solid solution. Part of the solute atoms diffuses along the vacancies and dislocations under the combined effect of interface energy, strain energy, and grain boundary energy. In addition, grain boundary segregation occurs and further leads to relatively coarse secondary phase. With the increase of temperature, discontinuous precipitation (DP), which occurs from the grain boundary to the grain internal, dominates the formation process of secondary phases. The phase transformation brings about significant precipitation strengthening, resultantly, enhances strength, and ductility are achieved for 7A60 aluminum alloy via ECAP. Moreover, the precipitation strengthening effect, which is closely related with the dissolution and DP, first enhances and then attenuates with the increase of ECAP passes. Dislocation strengthening and Hall‐Petch strengthening aggravate monotonically with the ECAP passes but play less important roles in the overall stress responses.