A Method for Comparing the Fatigue Performance of Forged AZ80 Magnesium

Andrew Gryguć,Xuming Su,Jim Prsa,Seyed Behzad Behravesh,Tom Sparrow,Alex Duquette,Rudy Gruber,Mary Wells,Bruce Williams,Hamid Jahed

doi:10.3390/met11081290

Abstract

A closed die forging process was developed to successfully forge an automotive suspension component from AZ80 Mg at a variety of different forging temperatures (300 °C, 450 °C). The properties of the forged component were compared and contrasted with other research works on forged AZ80 Mg at both an intermediate forging and full-scale component forging level. The monotonic response, as well as the stress and strain-controlled fatigue behaviours, were characterized for the forged materials. Stress, strain and energy-based fatigue data were used as a basis for comparison of the durability performance. The effects of the starting material, forging temperature, forging geometry/configuration were all studied and aided in developing a deeper understanding of the process-structure-properties relationship. In general, there is a larger improvement in the material properties due to forging with cast base material as the microstructural modification which enhances both the strength and ductility is more pronounced. In general, the optimum fatigue properties were achieved by using extruded base-material and forging using a closed-die process at higher strain rates and lower temperatures. The merits and drawbacks of various fatigue damage parameters (FDP’s) were investigated for predicting the fatigue behaviour of die-forged AZ80 Mg components, of those investigated, strain energy density (SED) proved to be the most robust method of comparison.

Highlights

The successful utilization of lightweight materials in structural applications is an engineering problem that requires a thorough understanding of the service environment of the component to fully achieve an optimal solution
Wrought forms of magnesium have been renowned for offering improved strength and ductility as they do not suffer from the manufacturing defects and coarse microstructure typical of cast manufacturing methods
The flattened billet was heated to the target forging temperature (300 and 450 ◦ C) for 1.5 h and isothermally forged using a 1500-ton hydraulic press using profiled upper and lower dies that were heated with complex internal geometry representing an automotive suspension lower control arm

Summary

Introduction

The successful utilization of lightweight materials in structural applications is an engineering problem that requires a thorough understanding of the service environment of the component to fully achieve an optimal solution. Mg components manufactured using traditional casting methods were utilized in applications where they were not significantly load-bearing and could offer significant reduction in mass compared to other structural metals (due to Mg’s low density). This was done without specific effort put into designing the manufacturing process, controlling the resulting material microstructure, or optimizing the component geometry for the applicationspecific service loads. Forging Mg to produce nearnet shape components can offer substantial benefit and facilitate the reliable usage of Mg in structural fatigue critical components This has necessitated an immense work towards understanding the complex structural behaviour of forged magnesium components as well as the development of the forging process to optimize the resulting material structure, properties and performance

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