Downloaded from SAE International by University of Michigan, Tuesday, April 02, 2019 SAE TECHNICAL PAPER SERIES 980470 Life Cycle Assessment of a Transmission Case: Magnesium vs. Aluminum Peter Reppe and Gregory Keoleian University of Michigan Rebecca Messick and Mia Costic Ford Motor Company International Congress and Exposition Detroit, Michigan February 23-26, 1998 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Downloaded from SAE International by University of Michigan, Tuesday, April 02, 2019 The appearance of this ISSN code at the bottom of this page indicates SAE’s consent that copies of the paper may be made for personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay a $7.00 per article copy fee through the Copyright Clearance Center, Inc. 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Printed in USA Downloaded from SAE International by University of Michigan, Tuesday, April 02, 2019 980470 Life Cycle Assessment of a Transmission Case: Magnesium vs. Aluminum Peter Reppe and Gregory Keoleian University of Michigan Rebecca Messick and Mia Costic Ford Motor Company Copyright © 1995 Society of Automotive Engineers, Inc. ABSTRACT panel beams, steering column components, seat frames, and engine valve covers [4] [5]. This paper describes a Life Cycle Assessment (LCA) In addition to the automotive light-weighting initiatives, done to evaluate the relative environmental performance there has been a recent trend of increased worldwide of magnesium (Mg) and aluminum (Al) automatic trans- environmental regulations. Accordingly, there is a current mission cases. Magnesium is considered a lighter weight need for better understanding of environmental burdens substitute for aluminum in this application. Light weight- of automobiles. Evaluating environmental metrics such ing of vehicles increases fuel economy and is an impor- as energy consumption; global warming potential; acidifi- tant vehicle design metric. cation potential; and air, water and solid waste emissions The objective of this LCA is to quantify energy and other helps to further this understanding. These metrics are environmental trade-offs associated with each alternative quantified using LCA as a tool. for material production, manufacturing, use, and end-of- Several car manufacturers have conducted limited stud- life management stages. Key features of the inventory ies in the past in order to compare the environmental bur- modeling and the data collection and analysis methods dens of design options involving magnesium with those are included in this paper along with life cycle inventory caused by traditional materials [6]. Typically, only energy profiles of aluminum and magnesium alternatives. The burdens for the use and material production phases have life cycle inventory (LCI) was interpreted using a set of been evaluated in these efforts, mostly due to the lack of environmental metrics and areas needing further available environmental data for other life cycle stages. research were identified. A qualitative cost assessment The LCA presented in this study compares environmen- was done in conjunction with this LCA to highlight poten- tal metrics for substituting the lighter weight metal mag- tial cost drivers. nesium for the currently used aluminum in an automatic car transmission case. Currently, only one other confi- INTRODUCTION dential study in Germany has attempted to quantify this comparison [7]. Ford’s Corporate Environmental Policy states that “con- sideration of potential health and environmental METHODS effects…is an early, integral part of the planning process" [1]. Additionally, there are efforts underway by automak- This LCA study was developed in accordance with the ers in Europe and North America to develop a new gen- Society of Environmental Toxicology and Chemistry eration of highly fuel-efficient, and lighter weight cars. (SETAC) guidelines with the exception of the impact Several associated research projects have been under- assessment [8]. Since impact assessment is a highly taken by Ford, including a Life Cycle Design study of an controversial part of LCA, a set of environmental metrics engine intake manifold [2], the development of a Design was tracked instead with the objective of highlighting spe- for the Environment (DFE) course for engineers, and the cific trade-offs. Data from the Eco-balance DEAMä development of recommendations for the design of database, published reports and direct contact with mate- lighter-weight vehicles (P2000) [3]. Past examples of rial suppliers were used to complete this study. magnesium being used in automotive applications include transmission cases, clutch housings, crankcases, intake manifold plenums, alternator brackets, instrument 1 Downloaded from SAE International by University of Michigan, Tuesday, April 02, 2019 PRODUCT SYSTEM stresses were induced with the magnesium case due to better dampening capabilities of the material. The 1995 Ford Contour transmission case was chosen The change from aluminum to magnesium would require for this study. It should be noted that Ford is not planning that the fasteners between the case and engine/con- to convert this transmission to magnesium. This compo- verter housing and the drain plug to have different sur- nent was chosen only as a model case study. One rea- face treatments. However, the excellent corrosion son this component was selected is that the plant that resistance of the considered magnesium alloy (AZ91 HP manufactures it does not manufacture any co-products. (HP=high purity)) rendered the application of any addi- Therefore, quantities such as materials used and wastes tional surface treatments for the case itself not necessary generated could be quantified by using totals shipped in [9], as the two materials are equivalent in this respect. It and out of the plant, facilitating the comparison of envi- was found that aluminum washers were required in the ronmental trade-offs between the aluminum and magne- magnesium design to prevent corrosion between steel sium. Equivalent performance parameters also had to be bolts and the magnesium metal. These washers were evaluated for the materials. These parameters are not modeled in this study. described below. The case is currently made of 100% secondary die-cast SCOPE AND SYSTEM BOUDARIES aluminum and weighs 9.435 kg. Experiences based on parts of other Ford vehicles as well as those from other This assessment evaluates the following life cycle stages Original Equipment Manufacturers (OEMs) [9] showed for the transmission case: raw material extraction, part that a weight reduction of 30% for the magnesium substi- manufacturing, car operation, and end-of-life manage- tution was reasonable to use for this study. Switching to ment. Refer to Figures 1 and 2 for the overall life cycle of magnesium initially raised concerns about mechanical the aluminum and magnesium cases, respectively. For stability due to the lower material strength of magnesium. this study, it was assumed that differences in the two The tensile strength of magnesium is 150 MPa versus transmission cases do not cause any differences in vehi- that of aluminum which is 160 MPa. In response to this, cle assembly. Vehicle assembly was therefore not a static stress assessment with a Finite Element (FE) included in this study. model was conducted. It was found that in fact lower life-cycle- material manu- end-of-life- use/operation stage production facturing management 6% 5% weight/kg 12.07 9.76 9.435 9.44 0.57 8.87 0.44 lost in shredding alloying abandoned operations, elements cars landfilled ingot, secondary 50% Al manufactured transmission in product cast case case use scrap liquid Al, 50% secondary alloying elements machining and scrap recoverd for scrap losses recycling weight/kg 2.31 0.32 8.43 95% processes remelting machining assembly dismantling