Project Background CONCLUSION AND RECOMMENDATIONS

1 CHAPTER 1 INTRODUCTION

1.1 Project Background

Aluminum alloy 7075 is a well known type of aluminum alloy used as structural materials of aerospace, transportation, and sports, where the need of lightweight and high strength are needed. Aluminum alloy 7075 is one of the 7000-series aluminum alloys, which captured its reputation in the aeronautical industries due to their attractive comprehensive properties, such as low density, high strength, ductility, toughness and resistance to fatigue Li et. al, 2007. However, like other 7000-series aluminium alloy, aluminium alloy 7075 is sensitive to localized corrosion such as intergranular corrosion, exfoliation corrosion and stress corrosion. Further enhancement is necessary in order to extend its further applications. Li et. al 2007 and Reda et al. 2008 stated that the corrosion resistance is modifiable via the means of heat treatment. Most of the researchers are favorable to study the effect on corrosion resistance of the aluminum alloy 7075 by comparing the other heat treatment processes to the T6 tempering of aluminum alloy 7075. Aluminum alloy 7075-T6 possesses high strength, but it is highly subjected to localized corrosion. Some heat treatment processes such as T73, T74, and T76 are developed to increase their corrosion resistance, especially T73 tempering, which is develop to enhance the resistance of the aluminum alloy 7075 against stress 2 corrosion. Besides of T73, another process named retrogression and re-aging or RRA is another heat treatment process which is well known to enhance the corrosion resistance of aluminum alloy. This project is done to study the effect of various heat treatment processes on the microstructure and stress corrosion cracking of aluminum alloy 7075. Heat treatment is applied on the material specimens to enhance their corrosion resistance against the stress corrosion cracking. Two different types of heat treatment processes, namely T73 tempering and RRA are applied on the aluminum alloy 7075, with T6 tempering as the reference. Direct tensile stress corrosion cracking test is done on the specimens, where later tensile test is done to determine the residual stress of the material after it undergone DTSCC. Besides, the tensile strength of the materials after DTSCC is then compared to the tensile strength of the materials which are not corroded under DTSCC, at which the difference of strength, indicates the occurrence of SCC within the materials. This cause of such properties is explained by relating with the microstructure appearance of specimens.

1.2 Problem Statement