High strength 7xxx Series Aluminium Alloys with Improved Damage Tolerance
The development of increasingly large commercial aircraft continues to set higher performance requirements for existing high-performance structural 7xxx aluminium alloys, and indeed to test the suitability of current alloys. In general, high strength 7xxx series alloys continue to exhibit inadequate resistance to stress corrosion cracking and/or reduced fracture toughness when applied in the peak-aged temper, which forces a compromise on properties employed in finished products. The Alcoa-developed alloy AA7150, subjected to so-called T7751 thermomechanical processing, represents one of the more recent and successful approaches to overcoming the above deficiencies, which have long-existed in 7xxx series alloy products.
This project, based on alloy AA7150, will involve strategic fundamental research designed to advance understanding of the strengthening and toughening mechanisms in latest-generation high-performance 7xxx series aerospace aluminium alloys, and to investigate novel heat treatment technologies, based upon the T77 ageing process. The project is commissioned as a 3-year project and will be cooperatively implemented within the newly-formed Australia-China International Centre for Light Alloy Research (ICLAR), by the ARC Centre of Excellence for Design in Light Metals, Monash University, Australia, and Southwest Aluminium (SWA) (Group) Corporation Limited, CHALCO, China.
Upon the implementation of this project, a substantially improved, in-depth understanding of the strengthening and toughening mechanisms for 7xxx series alloys will be obtained, along with the establishment of new heat treatment protocols. Near-term, it is anticipated that, largely through the implementation of novel heat treatment technologies developed within this project, CHALCO (through SWA) will be in a position to produce competitively alloy 7150 plate with property levels equivalent to those specified in USA Specification AMS4252B. Longer-term, the proposed research will define a platform for improved alloy design, giving rise to a new generation of high-performance alloys.
The accomplishment of this project will assist in the in-depth understanding of alloying methodologies, processing technologies, strengthening and toughening mechanisms for high performance 7xxx series aerospace aluminium alloys, and potentially enlarge their range of applications in the future aerospace industry of China. Thus, the development of alloys of novel composition within the 7xxx series, with increased strength, high damage tolerance and good stress corrosion resistance will be the longer-term priority.
It is to be expected that a new generation of AA7xxx alloys, coupled with novel processing technologies and advanced design concepts, will place CHALCO in a very favourable market position with respect to the rapidly emerging commercial aircraft/aerospace industries, both nationally and internationally.
As one of the largest aluminium companies globally, the Aluminium Corporation of China Limited (CHALCO) has targeted an emerging commercial aircraft industry for future growth in the application of aluminium alloys, and is devoting significant resources in support of this effort. For some years, CHALCO has conducted research and production assessment on Al-Zn-Mg alloys of the AA7xxx series used for such applications. However, there remain key issues to be resolved, which are beyond the current capabilities and facilities of CHALCO. The proposed project will thus address these key issues within the newly-formed Australia-China International Centre for Light Alloy Research (ICLAR), utilizing the combined capabilities of Monash University (and potential partner institutions) in cooperation with Southwest Aluminium (SWA) (Group) Corporation Limited.