Effects of Rare Earth Er Additions on Microstructure and Mechanical Properties of an Al–Zn–Mg–Cu Alloy

Abstract

The effects of Er additions on the microstructure and tensile properties of cast Al–15Zn–2.5Mg–2.5Cu aluminum alloy have been investigated. The results show that by adding 1 wt% Er grain refiner in the cast alloy, the grains can be refined to a fine degree. The microstructures and fracture surfaces of cast aluminum alloy samples were examined by SEM. In addition, the Er modified the eutectic structure from a coarse plate-like and acicular structure to a fine branched and fibrous one. The tensile properties were improved by the addition of Er, and good ultimate tensile strength (325 MPa) but poor elongation (6%) were obtained when the Er addition was 1 wt%. Furthermore, fractographic examinations revealed that refined pore and spheroidized a-Al dendrite were responsible for the high ultimate tensile strength. At higher magnifications, unrefined specimens showed cracking along the grains, whereas Er-refined specimens showed cracks in individual intermetallic compounds.