February 2023 Volume 5

MATERIALS

Allite, Inc. in Dayton, OH, is another specialty producer of magnesium forging stock. The company’s ZE62 forging grade alloy has an ultimate tensile strength of 350 MPa and a yield strength of 303 MPa, along with an elongation of 21%. 11 Another major consideration is the bending and flexing (or fatigue) loads that the forged magnesium components will be subject to over the design life of the vehicle, which is typically 15 years. Fatigue loads cause the part to lose strength over time. Suspension parts are subject to high fatigue loads, as are subframes. (Though it should be noted that fatigue is not much of a concern for the die castings utilized within the instrument panel or in the rear liftgate.) One limiting factor with fatigue is related to porosity or contaminants, such as oxides. These are the points where fatigue initiates and a crack begins to form. So, fatigue-driven forgings need high quality, clean metal, which cannot be easily obtained from Pidgeon processed alloys. Achieving the correct fatigue properties in the final component can be expensive to obtain due to the high number of cycles required in testing. In order to understand the fatigue strength of the material, engineers will bend a test piece back and forth over and over again until it breaks. Fatigue testing can last from 10,000 to 100,000 cycles, which takes a long time and makes it an expensive test, due to the machine usage cost. As a result, many material developers try to avoid it. However, this then shifts the risk to the user, who has to make a safe assumption about the fatigue life. Case Study – Automotive Suspension Arm: In 2018, a capable team led by Talal Paracha, a Masters student at the University of Waterloo, studied forged magnesium in an automotive suspension arm in comparison with a baseline casting.8 The other team members came from CanmetMATERIALS, Automotive Partnership Canada, Multimatic Technical Centre, and Ford Motor Company. The latter two were especially important for this development project, because Ford provided the key specifications for the components, while Multimatic is a well-respected Tier 1 supplier that is accustomed to forging automotive components and had the knowledge base to address the requirements of the control arm design. Completed over five years, the project resulted in a design that ultimately received the 2021 International Magnesium Association (IMA) Award of Excellence for Wrought Products. 12 During the development of the forging process to produce the control arm (Figure 1), the effect of forging temperature, forging rate, and material flow were simulated and optimized. The forging conditions went through many iterations in order to better understand the various parameters—friction, strain rate, and other conditions—that need to be “dialed-in” tomakemagnesium forging a commercial success. In order to ensure that the front lower control arm would be well suited to the harsh environment that automotive components are subjected to, the research team also developed coating technologies to increase the part’s corrosion resistance.

Figure 1: Forging sequence for the control arm.(8) The project resulted in the development of a high performance forged magnesium front lower control arm (Figure 2). The control arm delivered a 37% weight reduction compared to a comparable product in cast aluminum (1.53 kg for the forged magnesium version versus 2.43 kg for cast aluminum baseline), while also meeting the OEM’s performance requirements. This performance was confirmed through full-scale stiffness and durability testing.

Figure 2: Forged magnesium suspension arm. (Source: IMA.) Since the completion of the project, the research on the front lower control arm has continued with fatigue testing in a project led by Andrew Gryguc, University of Waterloo. 13 As with the previous project, this fatigue testing research was supported by CanmetMATERIALS, Automotive Partnership Canada, Multimatic Technical Centre, Centerline Windsor, and Ford. Currently, it is not clear as to whether the front lower control arm has entered commercial use. However, a study on suspension components completed in 2022 has shown that there is no known magnesium content within these components. 14 Of the front lower control arms researched in the 94-vehicle study, 10% are cast aluminum, 24% are forged aluminum, and the majority are welded steel. Beyond the forged magnesium suspension arm presented in the case study, a number of other components could also provide good opportunities for the use of forged magnesium components. Once a robust coating to protect against corrosion is developed, magnesium forgings could be used for gearboxes and covers, corner nodes for hybrid extrusion-based subframes, corner nodes for joining extrusions in EV battery boxes, frame nodes for the body-in-white, steering columns, and suspension arms and links. However, it should be noted that lightweighting generally happens from one material to another (i.e., steel to aluminum, aluminum to magnesium, etc.). Optimizing the form while using the same alloy (as in the case of using magnesium forgings to replace magnesium castings) is much less common.

FIA MAGAZINE | FEBRUARY 2023 38