Effect Of Macro Additions Of Zinc And Nickel On The Mechanical And Microstructural Properties Of A Modified 7xxx Aluminium Alloy
Andrew Idoko Haruna, Innocent Uduehi Abhulimen
KEYWORDS: hardening, intermetallic, mechanical properties, stir casting and tempering.
ABSTRACT: There has been large interest in combining the light weight of aluminium with varied excellent mechanical properties that a metal should poses for various industrial applications. This interest has led to vigorous researches in improving the mechanical properties of aluminium.This paper therefore investigatesthe effect of macro additions of zinc and nickel on the mechanical and microstructural properties of a modified 7xxx aluminium alloy. In this investigation, a corresponding relationship has been established between the microstructure and the properties of aluminium. Using the process of stir casting, Zinc was added to Al2.5Mg7Ni and Al2.5Mg2Ni to cast samples which were later homogenized at 550 oC and tempered (T6). Mechanical properties including, tensile strength, tensile elongation, hardness and fracture strength were investigated. Result shows that cast samples containing 15wt%Zn and 2wt%wtNi exhibited superior tensile strength (128.5MPa) and (0.0419) which is attributed to the presence and even distribution of Mg2Si and NiAl3 intermetallic, in the microstructure of the as-cast material. Solution treatment at 550oC led to a good combination of tensile strength and elongation (111.72MPa and 10%). Increase in Nickel content led to a stabilization of the material structure but did not impart strength and ductility. T6 tempering of solution treated samples did not give any increase in the mechanical properties. Microstructure of cast structure shows the presence of three intermetallic including NiAl3, AlFeSi and Mg2Si in the α-aluminium matrix.
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