Effects of Zn- And Mg-contents for increasing strength and ductility of Al-Zn-Mg alloys with trace Mn- And Ag-additions

Effects of Zn and Mg contents in Al-Zn-Mg alloys with Mn and Ag additions on the microstructures and mechanical properties were investigated. The increase in Zn content largely contributed to the increase in age hardenability of the alloy through the fine precipitation in grains, and the subsequent increase in Mg content contributed little to the increase in age hardenability. Tensile strength at the peak-aged condition increased with increasing Zn and Mg. On the other hand, the elongation decreased and the main fracture mode changed from transgranular fracture to intergranular fracture. The size of grain boundary precipitates of Zn-Mg alloys became lower by low temperature aging and two-step aging, which enables to increase both tensile strength and elongation, showing that mechanical properties can be improved by decreasing the grain boundary precipitate size even in the alloys to which Zn and Mg are added. © 2019 The Japan Institute of Light Metals