Automotive Uses of Magnesium Alloys: Part Two

---

Introduction to Automotive Magnesium Applications

The automotive industry represents one of the most promising markets for magnesium alloy applications, driven by the increasing demand for lightweight materials that enhance fuel efficiency without compromising performance. The body accounts for over 40% of total vehicle mass, with metals, primarily steel, serving as the first choice for structural components. While mechanisms utilize primarily metallic materials with increasing plastic component integration, most lightly stressed housings employ molded plastics.

Body Structure Applications and Opportunities

Space Frame Extrusions and Primary Structures

The most significant opportunity for wrought magnesium in automotive body applications lies in extrusions for primary structures, particularly space frames. Even if magnesium space frames do not achieve economic viability in the mass market, penetration in specialty automotive markets producing 50,000-100,000 units annually would substantially increase magnesium usage across the industry.

Additional opportunities exist in seat frame applications, where magnesium castings already demonstrate successful implementation. A strategic combination of castings, extrusions, and potentially sheet materials could prove competitive in these applications. However, implementing magnesium sheet in body panels requires developing economical, high-volume hot-forming processes that can match current steel and aluminum production capabilities.

Powertrain Components and Engine Applications

Engine and Transmission Housing Solutions

Powertrain components differ markedly from body applications, characterized by complex assemblies comprising numerous individual components utilizing diverse materials. Magnesium castings are progressively replacing iron and aluminum castings in various housings and covers throughout the powertrain system.

However, magnesium's limited creep resistance compared to aluminum prevents its use in the most massive and critical engine housings: the block and cylinder head. Conversely, transmission applications operating at substantially lower temperatures present excellent opportunities for magnesium to replace aluminum in massive main housings. Magnesium housings already demonstrate successful performance in transfer cases, validating this similar application approach.

Temperature and Performance Limitations

Powertrain applications require temperature stability up to 175°C, presenting challenges for magnesium implementation. The material's low high-temperature strength limits its use in critical engine components, though transmission and ancillary systems operating at lower temperatures remain viable applications. Wrought magnesium opportunities in powertrain components remain limited, as even wrought aluminum has gained minimal penetration in these applications.

Chassis Components and Structural Applications

Chassis components exhibit high diversity with characteristics bridging other automotive groups, featuring simpler mechanisms where many components serve dual structural functions. Materials remain diverse, with iron and steel maintaining major roles throughout chassis systems.

Components with significant structural functions, including suspension systems and sub-frames, continue steel domination, while those serving primarily mechanical functions, such as steering and brake systems, incorporate increasingly diverse materials. Aluminum gains market share among chassis housings and complex castings, creating substitution opportunities for magnesium, particularly in unsprung components where low mass provides key performance advantages.

Wheel Applications and Manufacturing Evolution

Historical Development and Racing Heritage

Wheels represented one of the earliest magnesium applications in automotive history. Development of competitive production processes based on welded extruded and stamped components enabled widespread implementation across various vehicle categories.

Following World War II, magnesium found expanded automotive applications, including frame and skin construction in racing vehicles such as the Mercedes 300SL and Porsche 962. The Volkswagen Beetle became the commercial vehicle with the largest single magnesium alloy application, featuring crankcase and transmission housing components totaling 17 kilograms. The production cessation of the air-cooled magnesium engine marked the end of a 50-year tradition in automotive magnesium applications.

Modern Wheel Technology and Production

Sand-cast magnesium wheels appeared in Porsche racing cars of the 1960s, including the 907, 908, 910, and 917 models, with standard production introduction in 1970 for the 914/916 models. This first generation of magnesium wheels, despite achieving service lives exceeding 150,000 kilometers, was discontinued due to insufficient understanding of die-cast technology, inadequate corrosion properties, and general economic recession in the 1970s.

Porsche initiated development of next-generation magnesium wheels produced through low-pressure die casting using PAZ9110 alloy. Contemporary magnesium wheels predominantly utilize forged construction with 11983 alloy to achieve superior strength and fatigue properties. Volkswagen/Audi's introduction of the B80 gearbox housing in 1996 launched a new era of drivetrain applications, significantly expanding the available application range.

Material Challenges and Limitations

Corrosion Resistance and Protection Strategies

Magnesium alloys face two major disadvantages in automotive applications: low high-temperature strength and relatively poor corrosion resistance. The introduction of high-purity alloys represented a major advancement in improving magnesium corrosion resistance. While alloying can enhance general corrosion behavior, it does not address galvanic corrosion problems when magnesium contacts other metals in the presence of electrolytes. Galvanic corrosion issues require proper coating system solutions.

Performance Property Limitations

Beyond galvanic corrosion concerns, low temperature strength presents serious limitations for magnesium, particularly in powertrain applications. The widespread transportation industry adoption of magnesium alloys faces constraints from various poor property profiles, including low creep resistance, high coefficient of thermal expansion, low Young's modulus, insufficient ductility, limited crash energy consumption in body structures, poor fatigue stability, and inadequate corrosion and wear resistance. These deficits require addressing through continued alloy and process development initiatives.

Surface Treatment and Coating Technologies

Electroplating and Decorative Applications

Electroplating of magnesium finds automotive industry application for decorative purposes, particularly for interior components. Enhanced corrosion resistance utilizes electroplating deposited as a top layer on conversion coating and special electrocoat layer systems. Such systems provide chromium top layers with 500-hour salt spray corrosion resistance. Many applications sufficiently protect the counterpart while leaving magnesium uncoated, provided it remains non-visible, as coating defects on magnesium result in enhanced localized corrosion attack.

Fastener Protection and Assembly Solutions

Anodized AlMg3 alloy causes no contact corrosion with magnesium components. Conventionally galvanized steel bolts can attach to magnesium using silicate sealing, successfully applied by Audi and Volkswagen for B80 magnesium gear housing applications.

Effective protection utilizes multi-layer coatings on critical counterparts, including zinc coating combined with cathodic dip-coating. Alternative approaches employ Sn/Zn coatings instead of conventional zinc galvanizing. New electrolytic deposited Al-Mg coatings for steel bolts remain under development and testing. Current solutions include insulating polymer coatings such as nylon or plastic caps for screw heads. Aluminum washers from 6XXX series alloys, sometimes anodized, or polymer washers used with steel bolts minimize contact corrosion on magnesium components.

Recyclability and Environmental Considerations

Energy Efficiency in Recycling

Recyclability represents an important consideration for automotive magnesium implementation. Metals generally demonstrate superior recyclability through melting and reuse processes. Magnesium particularly benefits from lower specific heat and melting point compared to other metals, providing energy advantages in recycling operations. Recycled magnesium requires approximately 4% of the energy needed for new material manufacturing.

Current Recycling Challenges and Future Development

Present recycling procedures remain incompletely developed, with ongoing work addressing technologies required for processing relatively clean factory waste materials. Future considerations may necessitate reviewing material flow to ensure recycled materials account for approximately ten percent of total magnesium alloy production capacity.

Conclusion

The automotive industry continues expanding magnesium alloy applications despite technical challenges requiring ongoing development. Success depends on addressing temperature limitations, improving corrosion resistance, and developing cost-effective manufacturing processes. The combination of weight reduction benefits, energy-efficient recyclability, and expanding application opportunities positions magnesium alloys as increasingly important materials for future automotive development.