Nanocluster Formation Behavior in Al-Zn-Mg Alloys with Microalloying Elements and Improved Mechanical Properties

Abstract

The formation behavior of nanoclusters and precipitates in Al-Zn-Mg alloys containing microalloying elements was investigated using TEM and 3DAP techniques. The grain size of the alloys was controlled to investigate its influence on the nanocluster formation. In the Al-Zn-Mg alloys, small amount of Mn is effective to refine grains. The age-hardening behavior and precipitate microstructures in the alloys with refined grains were complicated. In the grain refined alloy the age-hardening is markedly decreased and precipitation is greatly suppressed. It is found that the microalloying elements of Ag and Sn are effective to increase age-hardening and to produce refined precipitates in the refined grain alloy. The behavior is similar to the phenomenon of the reduced width of PFZs. The important feature of microalloying elements is the interactions with vacancies and solute atoms. The alloys with refined grains and reduced PFZs exhibit high strength and high ductility.