A Review of Magnesium Die-Castings for Closure Applications

Unlocking 50% Mass Reduction: The Case for Magnesium Die Cast Closures in Automotive Lightweighting

This technical summary is based on the academic paper "A review of magnesium die-castings for closure applications" by J.P. Weiler, published in Journal of Magnesium and Alloys 7 (2019).

Keywords

• Primary Keyword: Magnesium Die Casting for Closures
• Secondary Keywords: Automotive Lightweighting, Part Consolidation, Die-Casting, Closure Applications, Corrosion Mitigation, Vehicle Mass Reduction

Executive Summary

• The Challenge: Automotive manufacturers face immense pressure from fuel economy (CAFE) and emission standards, making significant vehicle mass reduction a critical industry-wide objective.
• The Method: This paper reviews past and current production applications and design studies of magnesium die-castings for automotive closure inners (e.g., liftgates, side doors, swing gates).
• The Key Breakthrough: Implementing magnesium die-cast inner panels for closures can achieve mass reductions of 40-50% and significant part consolidation, replacing multiple stamped steel components with a single casting.
• The Bottom Line: Magnesium die-castings are a proven, production-ready solution for achieving aggressive lightweighting targets in closure applications, offering substantial benefits in mass savings, part consolidation, and design integration.

The Challenge: Why This Research Matters for HPDC Professionals

The drive for improved fuel economy is relentless. Mandates like the Corporate Average Fleet Economy (CAFE) regulations, scheduled through MY 2025, are pushing automakers to explore every avenue for vehicle mass reduction. While powertrain advancements are crucial, lightweighting the vehicle body and structure offers profound benefits, including the potential for "compounded lightweighting"—where a lighter body allows for smaller engines, transmissions, and braking systems.

Traditionally, closures like doors and liftgates have been made from steel stampings. However, these assemblies are heavy, with the inner and outer panels accounting for up to 65% of the total mass. The challenge for engineers is to find a substitute that not only cuts weight dramatically but also meets stringent requirements for stiffness, crash performance, and manufacturability, all while integrating seamlessly into existing assembly lines. This paper reviews how magnesium die casting directly addresses this critical industry need.

The Approach: Unpacking the Methodology

This work is a comprehensive review of existing research and real-world production examples, demonstrating the viability and benefits of magnesium die-cast closures. The author analyzes a range of applications to distill best practices and common challenges.

Method 1: Analysis of Production Case Studies
The paper examines several high-profile production vehicles that have successfully implemented magnesium die-cast closures. These include:
- 2017 Chrysler Pacifica: A die-cast liftgate inner replaced nine stamped parts from the previous generation, resulting in an assembly weight reduction of nearly 50%.
- 2010 Lincoln MKT: Utilized a magnesium rear liftgate inner casting, achieving an approximate 40% mass reduction.
- 2018 Jeep Wrangler: Features a magnesium swing gate die-cast inner.
- Aston Martin DB9 & Vanquish S: Employed cast magnesium side door inners for an estimated 43% mass reduction.

Method 2: Review of Advanced Design Studies
The author also reviews detailed engineering studies that explored the potential of magnesium closures, including:
- DOE-Sponsored GM Project: Developed an integrated die-cast magnesium door inner that consolidated the header, beltline, hinge, and latch reinforcements into the casting, achieving a part count reduction and nearly 50% mass savings.
- Lotus Engineering Study (2009 Toyota Venza): An assessment that utilized over 26 kg of magnesium castings in side doors and a liftgate, resulting in a 41% mass reduction while passing extensive crashworthiness simulations.

The Breakthrough: Key Findings & Data

The review consolidates compelling evidence that magnesium die casting is not just a theoretical lightweighting solution, but a practical and highly effective one.

Finding 1: Consistent and Significant Mass Reduction of 40-50%

Across a wide range of production vehicles and design studies, the use of a magnesium die-cast inner panel consistently yields a mass reduction of 40-50% for the closure assembly compared to traditional steel designs. The 2017 Chrysler Pacifica liftgate is a prime example, achieving a weight reduction of nearly 50%. This direct mass saving is a primary driver for adoption.

Finding 2: Radical Part Consolidation and Design Integration

Magnesium die casting's design flexibility allows for the integration of multiple features and reinforcements into a single component. As noted in the Chrysler Pacifica case, a single magnesium casting replaced nine individual parts. This consolidation simplifies the supply chain, reduces assembly complexity, and allows designers to integrate features like local ribbing, integrated gussets, and varied wall thicknesses to meet stiffness and crash targets without adding separate reinforcement components.

Practical Implications for R&D and Operations

• For Process Engineers: The successful assembly of magnesium inners with aluminum outer panels relies on a well-defined process. This study highlights the importance of off-line pretreatment and coating (e.g., conversion coating followed by powder coat) for the magnesium casting prior to assembly. This process ensures corrosion protection, provides a clean surface for adhesive bonding during hemming, and protects BIW e-coat baths from magnesium dissolution.
• For Quality Control Teams: Galvanic corrosion is a primary concern. The findings emphasize that corrosion mitigation performance is "highly dependent upon the cleaning stages prior to the conversion coating." This suggests that QC protocols must rigorously monitor and validate surface preparation to ensure the long-term durability of the final assembly.
• For Design Engineers: The paper shows there is no single standardized design. Success requires leveraging the fluidity of magnesium to create advanced, one-piece designs with features like local ribbing and integrated gussets to manage stiffness (NVH) and crash loads. Furthermore, designing for multi-material systems is key, including strategies for isolating magnesium from steel fasteners and integrating aluminum components like intrusion beams or outer panels to manage galvanic potential.

Paper Details

A review of magnesium die-castings for closure applications

1. Overview:

• Title: A review of magnesium die-castings for closure applications
• Author: J.P. Weiler
• Year of publication: 2019
• Journal/academic society of publication: Journal of Magnesium and Alloys
• Keywords: Die-casting; Automotive applications; Closures; Lightweighting.

2. Abstract:

Vehicle mass reduction in the automotive industry has become an industry-wide objective. Increasing fuel efficiency and greenhouse gas emission targets for engine-powered vehicles, and ambitions for extended range electric vehicles have motivated these reductions in vehicle mass. Mass reduction opportunities in structural automotive applications are increasingly realized through lightweight alloy castings, such as magnesium, primarily due to the ease of component substitution. The traditional benefits of magnesium die-castings including lightweighting and associated compounded mass savings, excellent strength-to-weight ratio, part consolidation, near net-shape forming, dimensional repeatability, and integration of additional components can be realized in closure applications. One recent example is the application of a magnesium die-casting for the structural inner of the liftgate in the 2017 Chrysler Pacifica, replacing nine parts in the previous generation and resulting in a liftgate assembly weight reduction of nearly 50%. The work presented here reviews past and current developments of magnesium die-castings in closure applications and discusses the benefits and challenges of magnesium alloys for these applications, including casting design, corrosion and fastening strategies, and the manufacturing design and assembly methodologies.

3. Introduction:

The paper introduces the primary driver for vehicle lightweighting: the Corporate Average Fleet Economy (CAFE) regulations, which mandate improvements in fuel economy for North American vehicles through MY 2025. Vehicle lightweighting is identified as a key strategy to meet these standards. The introduction highlights that die-cast magnesium components achieve lightweighting through several methods: CAE optimization, the low relative density of magnesium alloys, and significant part consolidation. While traditionally used for instrument panel frames and seat frames, the paper notes that closure applications are a more recent area of investigation and production, with the potential to significantly increase the magnesium content in vehicles.

4. Summary of the study:

Background of the research topic:

The research is set against the backdrop of mandated automotive fuel economy improvements and greenhouse gas emission reductions. These regulations have made vehicle mass reduction a primary objective for the industry. Lightweight alloy castings, particularly magnesium, are presented as a key enabling technology.

Status of previous research:

The paper acknowledges the historical use of magnesium die-castings in applications like instrument panel frames, seat frames, and steering armatures. It notes that while several publications have investigated magnesium for closure applications, and a few production examples exist, its adoption has been limited despite significant demonstrated benefits in weight reduction and part consolidation. Challenges such as corrosion mitigation, fastening, and assembly strategies are identified as potential reasons for the limited production examples.

Purpose of the study:

The purpose of this work is to review past and current developments of magnesium die-castings in automotive closure applications. The study aims to discuss the benefits (e.g., mass reduction, part consolidation) and challenges (e.g., casting design, corrosion, fastening, assembly) associated with using magnesium alloys for these components.

Core study:

The core of the study is a literature review of production applications and engineering design studies focused on magnesium die-cast closure inners (side doors and liftgates). The paper synthesizes findings related to design strategies for stiffness and crash performance, manufacturing and assembly processes (including coating and joining with dissimilar materials), and methods for mitigating galvanic corrosion. It quantifies the mass savings and part consolidation achieved in various case studies and reviews CAE simulation results for crashworthiness.

5. Research Methodology

Research Design:

The study is a comprehensive review of published academic papers, technical reports, and conference proceedings. It synthesizes information from both commercial production programs and pre-production engineering studies.

Data Collection and Analysis Methods:

Data was collected from a range of sources, including SAE technical papers, industry conference proceedings (IMA World Magnesium Conference), and reports from government-sponsored projects (DOE) and research organizations (CAR, Lotus Engineering). The analysis involves comparing and contrasting the design approaches, manufacturing methodologies, performance results (mass reduction, stiffness, crash safety), and challenges reported across these different projects.

Research Topics and Scope:

The scope is focused specifically on magnesium die-castings used as the structural inner panel for automotive closures, including liftgates, side doors, and swing gates. The research topics covered are:
- Benefits: Mass reduction and part consolidation.
- Design Challenges: Achieving stiffness and crash requirements in an open-section casting.
- Manufacturing and Assembly: Pre-treatment, coating, and hemming processes with aluminum outer panels.
- Corrosion Mitigation: Strategies for managing galvanic corrosion in a multi-material assembly.

6. Key Results:

Key Results:

• Magnesium die-cast closure inners can achieve a mass reduction of 40-50% compared to traditional steel stamping assemblies.
• Significant part consolidation is a key benefit. The 2017 Chrysler Pacifica liftgate inner replaced nine parts with a single casting.
• Advanced casting design, incorporating local ribbing, integrated gussets, and variable wall thickness, is necessary to meet stiffness, NVH, and crash safety requirements.
• A common and effective assembly method involves pairing the magnesium inner with an aluminum sheet outer panel, joined by an adhesive bond and hemming operation, which helps mitigate galvanic corrosion.
• A multi-step coating process for the magnesium inner (e.g., conversion coating plus powder coating) is critical for corrosion protection and to ensure compatibility with the vehicle's body-in-white (BIW) e-coat process.
• CAE simulations and physical tests confirm that properly designed magnesium closure assemblies can meet or exceed the stiffness and crash performance of baseline steel doors.

Figure Name List:

• Fig. 1. 2017 Chrysler Pacifica showing the liftgate assembly highlighted by a magnesium die-cast inner [3] (Copyright 2018 by FCA. Used with permission).
• Fig. 2. Aston Martin Vanquish S with cast magnesium side door inners (Copyright 2017 by CAR Magazine, used with permission).
• Fig. 3. All-new 2018 Jeep Wrangler produced with a die-cast magnesium rear swing gate [3] (Copyright 2018 by FCA. Used with permission).
• Fig. 4. Integrated magnesium door cast inner developed as part of a DOE-sponsored project led by GM, right, and equivalent steel stamped door inner, left [10] (Copyright 2015 by IMA. Used with permission).
• Fig. 5. Mercedes SL Roadster die-cast magnesium door inner [19] (Copyright 2004 by Indian Institute of Metals. Used with permission).
• Fig. 6. Ford's concept die-cast magnesium door inner with an open architecture [16] (Copyright by The Minerals, Metals & Materials Society. Used with permission).
• Fig. 7. Integrated magnesium die-cast door inner designed as part of a DOE-sponsored project led by GM (Copyright 2018 by IMA. Used with permission, courtesy of GM).
• Fig. 8. Vehicle deformation resulting from 33.5 mph side barrier impact CAE simulations according to FVMSS 214 of the BIW structure in Ref. [9] (Copyright 2012 by CARB. Used with permission).
• Fig. 9. Simulated intrusion displacements resulting from 33.5 mph side barrier impact CAE simulations according to FVMSS 214 of the BIW structure in Ref. [9]. This simulation shows that there is a maximum B-pillar intrusion of 65 mm. The addition of the side door assemblies improve the response by 19% (Copyright 2012 by CARB. Used with permission).
• Fig. 10. Vehicle deformation resulting from 20 mph 75° side pole impact CAE simulations using a 50th percentile male crash dummy according to FMVSS 214 of the BIW structure in Ref. [9] (Copyright 2012 by CARB. Used with permission).
• Fig. 11. Simulated intrusions resulting from 20 mph 75° side pole impact CAE simulations using a 50th percentile male crash dummy according to FMVSS 214 of the BIW structure in Ref. [9]. This simulation shows that the intrusion is predicted to be less than 250mm (Copyright 2012 by CARB. Used with permission).
• Fig. 12. Door assembly containing the integrated magnesium die-cast door inner designed as part of a DOE-sponsored project led by GM (Copyright 2018 by IMA. Used with permission, courtesy of GM).

7. Conclusion:

The paper concludes that magnesium die-castings are excellent options for closure applications to help achieve future CAFE requirements through vehicle lightweighting. The review demonstrates that solutions exist for the primary technical challenges, including designing for stiffness and crash performance, developing a robust assembly and coating process, and implementing effective strategies to mitigate galvanic corrosion. The significant potential for mass savings and part consolidation, proven in both design studies and production vehicles, makes it a compelling technology.

8. References:

• [1] "Draft Technical Assessment Report, Midterm Evaluation of Light-Duty Vehicles Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards for Model Years 2022-2025", EPA, NHTSA, 2016.
• [2] USAMP team, Magnesium Vision 2020: A North American Automotive Strategic Vision for Magnesium, USCAR, 2006.
• [3] FCA North America media, media.fcanorthamerica.com, 2017.
• [4] M. Stevens, S. Modi, M. Chess, Mixed Materials Solutions: Alternative Materials for Door Assemblies, Center for Automotive Research, 2016 CAR Report.
• [5] J.P. Weiler, C. Sweet, A. Adams, R. Berkmortel, S. Rejc, C. Duke, Next generation magnesium liftgate - utilizing advanced technologies to maximize mass reduction in a high volume vehicle application, in: Proceedings of the 2016 IMA World Magnesium Conference, 2016.
• [6] P.J. Blanchard, G.T. Bretz, S. Subramanian, J.E. deVries, A. Syvret, A. MacDonald, and P. Jolley, "The Application of Magnesium Die Casting to Vehicle Closures", SAE Technical Paper Series 2005-01-0338, 2005, doi:10.4271/2005-01-0338.
• [7] IMA, "Magnesium Liftgate Improves Fuel Economy", Magnesium Showcase, 12 (2010), 2.
• [8] Lotus Engineering Inc., An Assessment of Mass Reduction Opportunities for a 2017-2020 Model Year Vehicle Program, The International Council on Clean Transportation, 2010.
• [9] Lotus Engineering Inc., Evaluating the Structure and Crashworthiness of a 2020 Model-Year, Mass-Reduced Crossover Vehicle using FEA Modeling, California Air Resource Board, 2012.
• [10] J. Jekl, J. Auld, Sweet C, J.T. Carter, S. Resch, A.D. Klarner, J. Brevick, A.A. Luo, Development of a thin-wall magnesium side door inner panel for automobiles, in: Proceedings of the 2015 IMA World Magnesium Conference, 2015.
• [11] P. Jonason, P. Nilsson, and M. Isacsson, "MAGDOOR Magnesium in Structural Application", SAE Technical Paper Series 1999-01-3198, 1999, doi:10.4271/1999-01-3198.
• [12] T. Ruden, R. Murty, and W. Ruch, "Design and Development of a Magnesium/Aluminum Door Frame", SAE Technical Paper Series 930413, 1993, doi:10.4271/930413.
• [13] C. Blawert, V. Heitmann, D. Höche, K.U. Kainer, H. Schrekenberger, P. Izquierdo, S.G. Klose, Design of hybrid Mg/Al components for the automotive body - preventing general and galvanic corrosion, in: Proceedings of the 2010 IMA World Magnesium Conference, 2010.
• [14] H. Schreckenberger, M. Papke and S. Eisenberg, "The Magnesium Hatchback of the 3-Liter Car: pProcessing and Corrosion Protection", SAE Technical Paper Series 2000-01-1123, 2000, doi:10.4271/2000-01-1123.
• [15] H. Friedrich, S. Schumann, J. Mater. Process. Technol. 117 (2001) 276–281, doi:10.1016/S0924-0136(01)00780-4.
• [16] G.T. Bretz, K.A. Lazarz, D.J. Hill, P.J. Blanchard, Magnesium Technology, TMS, Warrendale, PA, 2004, pp. 113–119.
• [17] Aston Martin global website, 2018.
• [18] Daimler Global Media, media.daimler.com, 2017.
• [19] C. Blawert, N. Hort, K.U. Kainer, Trans. Indian Inst. Metals 57 (2004) 397-408 doi:.
• [20] K. Dziczek, M. Schultz, T. Fiorelli, B. Swiecki, Y. Chen, D. Andrea, "New Materials/New Skills for the Trades", CAR Research, 2017.

Expert Q&A: Your Top Questions Answered

Q1: What specific design features are used in magnesium die-cast inners to compensate for magnesium's lower modulus compared to steel?

A1: The paper highlights that designers cannot simply substitute magnesium for steel. Instead, they must use an "advanced design" that leverages the die-casting process. This includes designing deep ribs and integrated gussets to create stiffness, adding local thickness additions in high-stress areas like hinge and latch regions, and creating a one-piece design that eliminates the flex associated with multi-part stamped assemblies.

Q2: How is the critical issue of galvanic corrosion addressed when a magnesium inner is assembled into a steel body-in-white (BIW)?

A2: The paper outlines a multi-faceted strategy. First, the magnesium inner is typically paired with an aluminum outer panel, which is much closer to magnesium in the galvanic series than steel. Second, the magnesium casting is pre-treated and coated (often with a powder coat) before assembly, creating a robust insulating barrier. Finally, any direct contact with steel parts or fasteners is managed through aluminum isolation or specialized fastener coatings.

Q3: Does consolidating multiple parts into one large casting create manufacturing challenges?

A3: While the paper focuses on the benefits, it implies that the manufacturing process must be highly optimized. The design of the Chrysler Pacifica liftgate, for instance, incorporated an aluminum stamping for the wiper reinforcement specifically to "optimize the manufacturing process." This suggests that while massive consolidation is possible, designers must balance the ideal single-piece design with practical manufacturing considerations for complex features.

Q4: What is the typical assembly process for joining the magnesium inner to the outer panel?

A4: The reviewed studies consistently describe a process where the aluminum outer is assembled to the magnesium inner using an adhesive bond combined with a hemming operation. The pre-applied coating on the magnesium inner provides a consistent and clean surface for the hem adhesive to bond to, ensuring a strong and durable joint.

Q5: Can these magnesium closures meet modern vehicle crash safety standards?

A5: Yes. The paper cites both CAE simulations and physical testing that demonstrate magnesium closure assemblies meet vehicle crash requirements. The Lotus Engineering study on the Toyota Venza, for example, subjected the design to extensive CAE simulations for side barrier impact and side pole impact, with positive results showing occupant restraint systems would retain functionality and intrusions were within acceptable limits.

Conclusion: Paving the Way for Higher Quality and Productivity

The core challenge of meeting aggressive automotive lightweighting targets requires proven, scalable solutions. This review demonstrates conclusively that Magnesium Die Casting for Closures is one such solution. By delivering mass reductions of up to 50%, enabling radical part consolidation, and meeting stringent performance criteria, the technology offers a clear path to helping automakers achieve their CAFE and emissions goals. The key takeaway is that the primary technical hurdles—design for stiffness, manufacturing assembly, and corrosion mitigation—have established, production-validated solutions.

"At CASTMAN, we are committed to applying the latest industry research to help our customers achieve higher productivity and quality. If the challenges discussed in this paper align with your operational goals, contact our engineering team to explore how these principles can be implemented in your components."

Copyright Information

This content is a summary and analysis based on the paper "A review of magnesium die-castings for closure applications" by "J.P. Weiler".

Source: https://doi.org/10.1016/j.jma.2019.02.005

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