Effect of Variation of Copper and Zinc Contents in Aluminium- Zinc-Copper Alloy

Abstract

In this work, the effect varying the copper and zinc contents on mechanical properties and microstructure of sand cast Al-Zn-Cu alloy was investigated. The tensile specimens of the as-cast and homogenized alloys were exposed to a solution heat treatment at 4000C for 4 hrs, followed by natural ageing in the room temperature. There were six different alloys and were characterized for optical light microscope, tensiometer and Rockwell B hardness test. Tensile and hardness tests were carried out to examine the effect of varying Cu and Zn contents and influence of solution heat treatment on the precipitation behaviour of the alloys. The results obtained showed that the addition of Cu increase in strength and hardness. There was accelerated precipitation kinetics with increase of Zn contents. The microstructure changes of the alloys were investigated by optical light microscope. The results show that severe dendritic segregation exists in Al-Zn-Cu sand cast alloy. It reveals segregation ("cording") within the dendrites and intermetallic between the dendrites as Cu and Zn contents were altered. There were a lot of eutectic phases at grain boundary and the distribution of these elements varies along interdendritic region.