Alan A. Luo

Recent magnesium alloy development for elevated temperature applications

Abstract Creep resistance is a major requirement for the use of magnesium in automotive powertrain components that are currently made of aluminium or cast iron. This paper summarises various new magnesium alloys that have been developed in recent years for elevated temperature applications. The alloy development basis, mechanical properties, creep resistance, bolt-load retention characteristics, and microstructure of seven new alloy systems (Mg–Al–RE, Mg–Al–Ca, Mg–Zn–Al–Ca, Mg–Al–Ca–RE, Mg–Al–Sr, Mg–Si, and Mg–RE–Zn; where RE represents mischmetal rare earth elements) are critically reviewed. The potential applications of these alloys in automotive powertrains are also discussed.

Magnesium: Current and potential automotive applications

In this paper, the material properties, structural performance, mass saving potential, design and manufacturing characteristics of magnesium are compared with various competing materials such as cast iron, steel sheet, aluminum alloys, and polymers. The current and potential automotive applications of magnesium are reviewed, and the technical challenges for these applications are also discussed.

Solidification Microstructure and Mechanical Properties of Cast Magnesium-Aluminum-Tin Alloys

The solidification microstructure and mechanical properties of as-cast Mg-Al-Sn alloys have been investigated using computational thermodynamics and experiments. The as-cast microstructure of Mg-Al-Sn alloys consists of α-Mg, Mg17Al12, and Mg2Sn phases. The amount of Mg17Al12 and Mg2Sn phases formed increases with increasing Al and Sn content and shows good agreement between the experimental results and the Scheil solidification calculations. Generally, the yield strength of as-cast alloys increases with Al and Sn content, whereas the ductility decreases. This study has confirmed an early development of Mg-7Al-2Sn alloy for structural applications and has led to a promising new Mg-7Al-5Sn alloy with significantly improved strength and ductility comparable with commercial AZ91 alloy.

Magnesium Alloy Development for Automotive Applications

This paper summarizes the development of new cast and wrought magnesium alloys using computational thermodynamics tools and experimental approach. The Mg-Al-Ca alloys show excellent creep resistance due to the formation of high-temperature (Mg,Al)2Ca phase. The Mg-Al-Sn alloys are designed for mechanical properties and corrosion resistance through the optimization of Mg17Al12 and Mg2Sn phases in the microstructure. In the Mg-Zn-Ce system, Zn provides strength through solid solution strengthening while Ce increases the ductility via improved texture. Mg-Nd-Zn is a heat-treatable alloy system based on the precipitation hardening of Mg12Nd phase.

Wrought Magnesium Alloys and Manufacturing Processes for Automotive Applications

In this paper, the mechanical properties, structural performance and mass saving potential of wrought magnesium alloys are compared to several major automotive materials: mild steel, advanced high-strength steel, cast and wrought aluminum, cast magnesium, plastics and fiber-reinforced composites. Manufacturing processes including welding and joining of magnesium extrusions and sheet products are critically reviewed. The current and potential applications of wrought magnesium alloys in automotive interior, body and chassis areas are discussed. Technical challenges and research opportunities for these applications are identified.

Directional Solidification and Microsegregation in a Magnesium-Aluminum-Calcium Alloy

Creep-resistant Mg-4Al-4Ca (AX44) alloy was solidified under different growth/cooling rates using a directional solidification (DS) technique. The solidification behavior and microsegregation of the alloying elements in the castings was investigated. Computational thermodynamics calculations of phase equilibria and experimental observations confirm that the solidification microstructure in this alloy consists of α-Mg, C36-(Mg,Al)2Ca, and C14-Mg2Ca phases. A relationship was established between the primary dendrite arm spacing and the cooling rate, which can be used to predict mechanical properties such as yield strength and creep. The microsegregation of alloying elements (Al and Ca) predicted by the Scheil model in AX44 agrees well with the electron probe microanalysis (EPMA) measurements, suggesting that the Scheil model can be used in microstructure simulation of magnesium castings.

Development of a Moderate Temperature Bending Process for Magnesium Alloy Extrusions

An appropriate temperature (150-200°C) bending process has been developed for AZ31 and AM30 magnesium alloy tubes, and the optimum bending process parameters were obtained using a Design of Experiments (DOE) method. The development of this process was one of the key factors for use of magnesium tubes in automotive components for vehicle weight reduction. The tensile properties and deformation microstructure of magnesium alloys at elevated temperatures indicated that temperature of 150-200°C which might be suitable for hydroforming and other forming processes.

Materials Comparison and Potential Applications of Magnesium in Automobiles

In this paper, the material properties, structural performance, mass saving potential, design and manufacturing characteristics of magnesium are compared with various competing materials such as cast iron, steel sheet, aluminum alloys and polymers. The current and potential automotive applications of magnesium are reviewed, and the technical challenges for these applications are also discussed. Recent alloy development for powertrain applications and the creep resistance of several experimental magnesium alloys are reviewed.

Study on Pressurized Solidification Behavior and Microstructure Characteristics of Squeeze Casting Magnesium Alloy AZ91D

Squeeze casting technology for magnesium alloys has a great application potential in automobile manufacturing and has received increasing attention from both academic and industrial communities. In this study, the pressurized solidification behavior of magnesium alloy AZ91D in squeeze casting process was investigated using computer-aided cooling curve analysis (CA-CCA). It was found that the applied pressure increased both the start and end temperatures of primary α-Mg formation but had little effect on the sizes of temperature ranges. Moreover, the applied pressure increased the start temperature and decreased the end temperature of eutectic reaction during the solidification, resulting in a larger temperature range of eutectic reaction compared with solidification under atmospheric pressure. The grains were remarkably refined, and the eutectic fraction increased with increasing applied pressure. The dendritic microstructure with a larger secondary dendrite arm spacing (SDAS) was observed under a higher applied pressure at the central part of the experimental casting. By correlating the CA-CCA and SDAS data, it was found that SDAS and the cooling rate at the maximum α-Mg growth could be fit into the power law equation in classic solidification theories.

Applications: aerospace, automotive and other structural applications of magnesium

This chapter discusses the material properties and mass saving potential of magnesium alloys in comparison with major structural materials: mild steel, advanced high-strength steel (AHSS), aluminum, polymers, and polymer composites. The alloy development and manufacturing processes of cast and wrought magnesium alloys are summarized. Structural applications of magnesium alloys in automotive, aerospace, and power tools industries are reviewed in this chapter. The opportunities and challenges of magnesium alloys for structural applications are discussed.