Effects of solution treatment on microstructural and mechanical properties of Al-Zn-Mg alloy by microalloying with Sc and Zr

The effects of solution treatment on microstructural and mechanical properties of a novel Al-Zn-Mg alloy by microalloying with Sc and Zr were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transition electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimeter (DSC), X-ray diffraction and tensile test, hardness measurement, respectively. The results show that solution treatment had a significantly effect on microstructural and mechanical properties. There exist lots of residual phases along rolling direction before solution treatment. With increasing solution temperature/time, the residual phases are dissolved into alpha-Al matrix gradually, and the number density of residual phases decreased. After solution treatment at 460 degrees C/60 min and aging treatment at 120 degrees C/24 h, the precipitated phase inside the grains are homogenously distributed eta' phase; the distribution of eta precipitates is discontinuous and coarsened on the grain boundary. With the increase of solution temperature(<= 470 degrees C) or solution time(<= 60 min), the precipitated phases inside the grains began to become more diffuse, and the grain boundary precipitated phases also gradually become smaller. When solution temperature further increased to 490 degrees C or solution time increased to 120 min, the precipitated phases within the grains and on the grain boundary began to coarsen. In addition, there also exists lots of fine Al-3(Sc, Zr) particles during aging treatment. Both tensile strength and hardness increase first and then decrease with increasing solution temperature or solution time. The optimum solution treatment is 470 degrees C/60 min. The ultimate tensile strength, yield strength and elongation of the aged studied alloys reached a maximum value, 581 MPa, 561 MPa, and 10.1%, respectively. (C) 2016 Elsevier B.V. All rights reserved.