Retrogression And Reaging (RRA) Treatment Process And The Effect On Microstructure And Mechanical Properties Of Aluminium Alloy 7075

Mohd Nazizi, Sungip (2009) Retrogression And Reaging (RRA) Treatment Process And The Effect On Microstructure And Mechanical Properties Of Aluminium Alloy 7075. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

A new pattern of heat treatment is produced known as retrogression and reaging (RRA) heat treatment to increase strength and hardness of aluminium alloy 7075 due to the need of high strength in application such as in aerospace industry. From the previous study, RRA heat treatment is done in two stages; retrogression process and reaging process. In this project, aluminium alloy 7075 is studied to determine its mechanical behaviour as an effect of RRA heat treatment. During retrogression process, materials are subjected at 200 o C for 5, 10, 20 and 40 minutes and followed by reaging process which is carried out at 120 o C for 24 hours. The material is tested for hardness and impact energy profile after RRA treatments. These profiles showed that the strength and toughness of material is exhibited slightly higher than original T6 temper. These increments are much related to the microstructural characteristic of the material. In the T6 temper, the structure primarily consists of a fine distribution of n' particles. The initial decrease in strength during the retrogression treatment is mainly due to the dissolution of small n' particles. During this condition, coarsening of grain boundary precipitates occurs resulting in an increase in the volume fraction of grain boundary precipitates as same with microstructure of T73. The function of the reaging is to promote re-precipitating of n'. The microstructure is similar with T6 but slightly denser and coarser and mores stable in nature. Thus, the used of RRA treatment is been a good way in enhancing the mechanical properties of aluminium alloy 7075.

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