Microstructural Evaluation and Mechanical Properties of an Al-Zn-Mg-Cu-Alloy after Addition of Nickel under RRA Conditions

Abstract

The effects of nickel in improving the mechanical properties and microstructure of Al-Zn-Mg-Cu alloys produced by semi-direct chill casting were investigated. Aluminium alloys were homogenized at different temperatures conditions, which aged at 120˚C for 24 h (T6 temper), and retrogressed at 180˚C for 30 min and then re-aged at 120˚C for 24 h (RRA). The results of the microstructural analyses showed that with adding nickel to aluminium alloy, nickel-rich dis- persoid particles were formed, such as Al7Cu4Ni, Al4Ni3, Al75Ni10Fe15, Al3Ni2, and Al50Mg48Ni7. Intermetallics com- pounds within the matrix alloy led to dispersion and fine-grain mechanisms which prevent the recrystallization and grain growth. Enhancement of mechanical properties of the alloys study is obtained through the precipitation hardening of alloying elements of the base alloy besides Ni-bearing dispersoid particles. The microstructure of these alloys was examined through optical and scanning electron microscopy along with energy dispersive X-ray and X-ray diffraction.