IJSRSET151467 | Received: 16 August 2015 | Accepted: 09 October 2015 | September-October 2015 [(1)5: 225-228] © 2015 IJSRSET | Volume 1 | Issue 5 | Print ISSN : 2395-1990 | Online ISSN : 2394-4099 Themed Section: Engineering and Technology 225 Effect of Variation of Copper and Zinc Contents in Aluminium- Zinc-Copper Alloy Sani A. Salihu 1 , Suleiman I. Yakubu 2 , Aliyu Isah 3 Department of Metallurgical and Materials Engineering Technology, Waziri Umaru Federal Polytechnic, Kebbi State, Nigeria 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. Keywords: Al-Zn-Cu Alloy, Solution Treatment, precipitation, Hardness, Dendrites Microstructure I. INTRODUCTION Aluminium and the aluminium alloys lend themselves to many engineering applications because of their excellent combination of lightness with strength, their high corrosion resistance, their thermal and electrical conductivity and heat and light reflectivity, and their hygienic and non-toxic qualities (A.M. Zahra et al, 1990 and Vadim S., et al, 2007). The variety of forms in which they are available also enhances their utility (Patricia et al, 2009). Aluminium alloys are widely used in constructions of light components at aerospace and automotive industry. There are two main classes of aluminium alloys, they are wrought alloys and cast alloys. The 7xxx alloys are among the eight cast aluminium alloys that are used for aerospace and automotive applications. There are several alloys in the series that are produced especially for their high toughness, notably 7075, 7136, 7150, and 7475, both with controlled impurity level to maximize the combination of strength and fracture toughness. These alloys are heat treatable and among which are the Al-Zn-Mg-Cu versions that provide the highest strengths of all aluminium alloys (ASM, 1991 and ASM 2004). The 7000 series is made up of Al-Zn-Cu-Mg alloys where Zn is the strengthening component (Anikumar et al 2011 and Yin Dongsong et al 2009). High strength aluminium alloys of Al-Zn-Cu-Mg series are widely used in automotive and aerospace field due to their high specific strength, toughness and fatigue durability (Grard, 1920, Prabhu, et, al, 2011 and Yin Dongsong,et, al, 2009). The common feature of these alloys is high volume fraction of alloying elements, which leads to severe dendrite and grain boundary segregation in the as-cast alloy. It is well known that the type and intrinsic characteristic of residual phases will differ in different alloys and change with different heat treatment conditions. "Mondal and Mukhopadhyay" (Muzaffer Zeren, et, al, 2011) studied the phases in the as-cast and homogenized 7055 aluminium alloys, and revealed that the major residual phases were Ș (MgZn2 ), T (Al2 Mg3Zn3), S (Al2CuMg) and ș (CuAl2 ). The microstructure of the cast 7050 alloy consists of dendrites, high angle grain boundaries, and inter-