Effect of the Zn/Mg Ratio on Microstructure and Mechanical Properties in Al-Zn-Mg Alloys

Abstract

It is well know that the 7000 series Al-Zn-Mg alloy has good age hardening ability and high strength among commercial aluminum alloys. In this study, hardness measurement, tensile test, SEM and TEM observation have been performed in order to understand the effect of the Zn/Mg ratio on age hardening behaviour in Al-Zn-Mg alloys. It was seen from hardness measurement that the peak hardness increased with increasing amount of Zn and Mg. Tensile tests were performed for the samples of peak aged condition. It was seen that UTS increased with increasing amount of the Zn and Mg. The elongation decreased with increasing the amount of the Zn and Mg. Intregranular fracture was observed in alloys with low amount of Zn and Mg.Transgranular fracture was observed with high amount of Zn and Mg alloy. TEM observation was performed for peak aged samples. The size of precipitates became finer and the number density increased with increasing Zn and Mg contents.T’ Phase and h1 phase were observed in low Zn/Mg alloy. The h’ phase was observed in high Zn/Mg alloy.