Development of Advanced Al-Mg-Si(-Cu) Alloy Technology for Automotive Body Panels
During the past decade, the international demand for energy-efficient, lightweight vehicles has seen aluminium alloys make increasing inroads into the automotive sector, where they replace, for the large part, steel components. This intrusion has been most notable in vehicles at the prestige end of the market, but there is encouraging recent evidence of the use of selected aluminium alloys in, for example, sheet for body panels in larger volume models. Such applications reflect, in part, normal competition in materials selection but, increasingly, also changes in the economics of vehicle manufacture as fuel costs increase sharply. For such applications to continue to expand in larger volume sectors of this market, it will be necessary for continued significant improvements in processing efficiency and properties to be achieved, with simultaneous reductions in manufacturing costs.
The primary automotive sheet requirements, which include adequate mechanical properties, formability and surface quality, combined with paint-bake strength (for dent resistance) and corrosion resistance, are most commonly met in heat treatable Al-Mg-Si(-Cu) alloys of the 6xxx series. However, such alloys are not thermally stable at room temperature after solution treatment and quenching, and their tendency to natural ageing prejudices the subsequent paint-bake response. Furthermore, the dwell time during the paint-bake treatment is usually insufficient to optimise strength and hardness. The full potential of Al-Mg-Si(-Cu) alloys is consequently yet to be fully realised, and the proposed project is directed to optimization of composition and processing conditions to preserve primary sheet requirements, while increasing the strength of Al-Mg-Si(-Cu) alloys in the paint-baked condition.
As one of the largest aluminium companies globally, the Aluminium Corporation of China Limited (CHALCO) has targeted the automotive industry for future growth in the application of aluminium alloys, and has devoted significant resources in support of this effort. For some years, CHALCO has conducted research and production assessment on Al-Mg-Si(-Cu) alloys used for automotive body panels.
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 Suzhou Institute for Nonferrous Metals Research (SINR). Specific research objectives will include:
i)	Resolution of the mechanisms of natural ageing and pre-ageing in Al-Mg-Si(-Cu) alloys, and their effects on the subsequent paint-bake response. The research will involve detailed experimental characterization and modeling of pre-precipitate clustering, and coherent and partially-coherent precipitation, and the assessment of their effects on microstructural evolution.
ii)	Investigation and optimization of approaches to enhancing the precipitation kinetics during the paint-bake treatment, with a view to achieving optimum mechanical properties in a commercially feasible paint-bake cycle.
iii)	Investigation and optimization of approaches to enhancing the precipitation kinetics during the paint-bake treatment, with a view to achieving optimum mechanical properties in a commercially feasible paint-bake cycle.
The strategic objectives of the project will include:
i)	Resolution of the key issues in the production of 6A11 and 6A22 alloys developed by the Southwest Aluminum (Group) Co. Limited (SWA) and SINR.
ii)	Development of a set of alloy specifications that place CHALCO in an internationally competitive position as a preferred supplier of 6xxx series aluminium alloy sheet to both the national and international automotive industries.
iii)	Establishment of a solid research foundation for the development of new classes of aluminium alloys for use in the automotive industry and in other sectors.