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Molten magnesium is a highly reactive metal that unlike many other metals (eg. aluminium), is not well protected from further oxidation by its own natural oxide film. Thus, molten magnesium burns in air unless it can be protected by some means. Cover gas systems act to change the characteristics of the oxide film so that the film adheres well to the underlying molten magnesium, self-repairs when disturbed or broken, and provides effective protection from further oxidation.
Economic Benefits of Using AM-cover to Magnesium Diecasters
Loss of magnesium metal due to oxidation decreases the economic performance of diecasting plants and increases environmental problems arising from difficult-to-recycle dross and sludge. The choice of an effective cover gas system, together with efficient furnace closures and melt handling systems, enables molten magnesium to be handled without excessive oxidation or burning and provides an opportunity for diecasters to reduce costs.
Environmental Benefits of Using AM-cover to Magnesium Diecasters
Sulphur hexafluoride (SF6) is the most widely used means of protecting molten magnesium and its alloys from burning. At the time of its introduction in the 1970s, the use of SF6 for this purpose was a significant breakthrough for the magnesium production and diecasting industry. However, SF6 has an extremely high Global Warming Potential (GWP), with a CO2-equivalent 22 200 times greater than carbon dioxide. It is listed in the Kyoto Protocol as a gas to be reduced in industrial usage. The EU and a large number of nations, including USA, are undertaking measures to ban or strictly limit its use for the protection of magnesium. An EU directive will ban the use of SF6 for protection of magnesium by all users, whose consumption of SF6 exceeds 500 kg pa, from January 2007. The global magnesium industry is looking for an environmentally friendly solution.
Commercial Opportunity for AM-cover with Magnesium Diecasters
There is a significant market opportunity for a cover gas system that performs the same function as SF6, has a potential for cost-reduction, and does not have the environmental disadvantages of SF6.
Evolution of AM-cover Magnesium Technology
AM-cover was developed by the former Australian Magnesium Corporation and CAST in a 4 year program of research and development. The technology has now been taken over by Advanced Magnesium Technolgies and has been extensively tested in a range of industrial environments. AM-cover is now being promoted in the market by Advanced Magnesium Technolgies as an effective replacement for SF6 cover gas mixtures. It is a low cost, safe, and environmentally friendly cover gas system that has been shown in a joint program with the US Environmental Protection Agency (USEPA) to reduce greenhouse gas emissions by more than 99% compared to normal practice with SF6 gas mixtures. Several diecasters in North America and Europe have either converted their entire operation to AM-cover or are in the process of converting. The USEPA recently recognised Advanced Magnesium Technolgies’ contributions to US industry by awarding it a Certificate of Recognition for the introduction of this new environmentally friendly technology.
Environmental and Economic Effects of Using AM-cover
The active chemical constituent of AM-cover is HFC-134a which is widely used as a refrigerant gas and is commonly present in automobile air conditioning systems. AM-cover uses HFC-134a in a dilute mixture with a carrier gas such as N2 nitrogen or CO2 carbon dioxide. HFC-134a has a GWP of 1320 but, in the high temperature furnace environment above molten magnesium, 80-90% of the HFC-134a that is used in AM-cover decomposes so that total greenhouse emissions are kept to a minimum. Use of AM-cover for magnesium melt protection typically results in a 95-99% reduction of greenhouse gas emissions compared to SF6 cover gas mixtures and reduces costs by minimising the generation of dross and sludge. The cost of the gas itself is also cheaper than SF6.
Health and Safety Issues Associated with AM-cover and Magnesium Diecasting
Much of the research on AM-cover has been concerned with thermal decomposition products and associated occupational health and safety issues. Extensive laboratory experiments and industry-scale trials have characterised the decomposition process and enabled the development of safe operating conditions. This work has been independently renewed and approved by an Associate Professor of Medicine and Respiratory Physician at a leading Brisbane hospital.
Worldwide Patents and AM-cover
Worldwide patents have been applied for to protect the AM-cover technology. Patents have already been granted in 5 five countries and are expected to be issued in Europe and USA in the near future. Advanced Magnesium Technolgies has exclusive worldwide rights to commercialise the use of AM-cover.
Commercial Availability of AM-cover
Marketing of the technology is currently taking place predominantly in Europe. Diecasters in Europe are particularly interested in the technology because of the forthcoming EU ban on usage of SF6 that is planned to come in effect from January 2007. The main competing technology involves the use of sulphur dioxide which, while cheaper, is harmful to health and contributes to pollution from acid rain. To date seven diecasters have signed licence agreements for use of AM-cover and a number of these are already in the process of implementing plant-wide conversions. The technology is licensed under long term agreements at a benchmark price of EUR 10 per tonne of castings produced per annum. There are currently approximately 150,000 tonnes of magnesium castings produced annually. It is expected that over the next few years AM-cover will become the technology-of-choice for the whole magnesium industry, including producers, recyclers and diecasters.
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