Effect Of Macro Additions Of Zinc And Nickel On The Mechanical And Microstructural Properties Of A Modified 7xxx Aluminium Alloy
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 o C 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 550 o C 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.
Effects of pre-stretching and ageing on the strength and fracture toughness of aluminum alloy 7050
The effects of the pre-stretching and ageing on the microstructure, strength and fracture toughness of the 7050 aluminum alloy were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile test and the plane-strain fracture toughness test. The results indicate that the peak aged 7050 aluminum alloy possesses a higher strength, but its fracture toughness is poor. The high temperature and a subsequent low temperature ageing improve the fracture toughness by 8% while the strength is decreased by 3.5%. The fracture toughness of the over aged 7050 aluminum alloy is enhanced by 29% with a decrease in the strength of 7%. The retrogression and reaging provides an optimum combination of the strength and fracture toughness, which improves the fracture toughness by 17% without sacrificing the strength. After the pre-stretching, the precipitates within grains become coarse for all the ageing tempers which results in a lower strength. While the strength difference between the matrix and the grain boundary become lower and the area fraction of the grain boundary precipitates become smaller, leading to the higher fracture toughness.
Investigation on strength, toughness and microstructure of an Al–Zn–Mg–Cu alloy pre-stretched thick plates in various ageing tempers
Abstract The 7B04 Al alloy is a precipitation hardenable, plate and forging material, which is widely used in China for strength critical aerospace structural applications. In this paper, fracture toughness, electrical conductivity and tensile properties of the alloy were investigated, and their dependence on ageing treatment details was described. Varying the heat treatment details strongly influences the microstructure and properties of the alloy. The alloy is identified to respond well to retrogression and reageing (RRA) temper. The retrogressing treated material at 180 °C for 1 h and then reageing for 22 h at 120 °C can achieve tensile properties comparable to a T6 condition as well as excellent conductivity. The high strength associated with optimized RRA conditions tend to result in relatively low levels of fracture toughness, but still slightly higher than T651 condition treated material. A correlation has been made among such properties, microstructure and fracture behavior, as characterized using TEM and SEM observations, and the results are discussed in the light of this relationship.