Microstructural Effects of Zn/Mg Ratio and Post Heat Treatment on Tensile Properties of Friction Stirred Process (FSP) Al–xZn–yMg Alloys

Abstract

The workability and ductility of Al–Zn–Mg alloy are lower. In this study, the Zn content (4.44–6.34 mass%) was reduced and the Mg content (1.11–1.28 mass%) was raised to investigate the relationship between microstructures and tensile mechanical properties of Al–xZn–yMg aluminum alloys after friction stir process (FSP). The ZM35 alloy (Zn/Mg ratio is 3.5) and the ZM57 alloy (Zn/Mg ratio is 5.7) had a friction stir process and then three artificial aging treatments were performed to discuss the effects of Zn/Mg ratio on mechanical properties. After FSP and then natural aging for 12 days, the results of the experiment showed that the tensile strengths of ZM35 and ZM57 alloys were lower than the base metal (extruded material with T6, no FSP). Notably, the strength of as-FSP specimens was promoted after aging treatments. Through the mode I (80°C/16 h) treatments and the mode II (80°C/16 h + T6) treatment, the strengths of ZM35 alloy and ZM57 alloy were improved. However, after the mode III (T4 + 80°C/16 h + T6) treatment, the tensile strength and ductility of the ZM57 alloy reduced, and the deterioration rate of ductility reached to 65%; the ZM35 alloy possessed a better ductility, which confirmed the fact that decreasing Zn/Mg ratio improved the workability of friction stir Al–Zn–Mg specimens with an artificial aging treatments.