Impacts of High-Pressure Diecasting Process Parameters on Greenhouse Gas Emissions
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NTRODUCTION
ALUMINUM and magnesium alloy components made using the high-pressure diecasting (HPDC) process are among the highest-volume items manufactured by the metalworking industry. Cost advantages derived from its high productivity rates have made HPDC the process of choice for mass producing castings destined for automotive, commercial, and consumer applications. In addition, the growing focus on making automobiles lighter through the increased use of light alloy components is expected to drive an anticipated growth of the HPDC industry well into the future. Major activities surrounding the HPDC process, dealt with in detail elsewhere,[1,2] are captured in Figure 1 for the aluminum and magnesium alloy foundries studied in this work. Inputs to the foundries include raw material, energy, and consumables. Outputs are comprised of shipped castings and emissions to air and water. Differences in material flows exist between scrapped aluminum, which is typically recycled in-house, and D.R. GUNASEGARAM, Senior Research Scientist, is with CAST Cooperative Research Center (CAST CRC) and CSIRO Light Metals Flagship, Clayton, VIC 3169, Australia. A. THARUMARAJAH, Principal Research Scientist, is with CAST CRC and CSIRO Sustainable Ecosystems, Highett, VIC 3190, Australia. Contact e-mail: [email protected] Manuscript submitted November 6, 2008. Article published online May 21, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
scrapped magnesium, which is sold primarily to external recyclers. While the energy requirements of manufacturing activities such as HPDC are approximately an order of magnitude lower than those for manufacturing activities such as materials extraction and primary processing, they often set many of the requirements for the upstream processes.[3] Greenhouse gas (GHG) emissions attributable to primary processing in aluminum and magnesium may be traced to the use of fossil-fuelderived energy and some reactions in various stages of the extraction and refinement. The use of the potent GHG gas sulfur hexafluoride (SF6) as a cover during magnesium melting and holding at the foundry is also a major contributing factor to emissions. It is now generally accepted that climate change can be attributed to the greenhouse effect.[4] Despite the importance of the HPDC industry, the effects of HPDC process parameters on GHG emissions are not widely reported in the public domain. Neto et al.[5] developed a model that related the aluminum alloy HPDC to an overall environmental impact index M, which was composed of eight environmental issues, including global warming. When these issues were given equal weighting, their model predicted that a ±20 pct change in the HPDC material yield would change M by 12 and +17 pct, respectively, and a ±20 pct change in scrap would change M by ±2 pct. Neto et al. did not report the impact on GHGs separately. Tan and Khoo[6] determined that a 20 pct reduction in scrap at an VOLUME 40B, AUGUST 2009—605
Electricity
Natural gas
Consumables
Material preparation
CASTING PLANT
Scrap
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