Tailor made Magnesium Alloy for Selective Laser Melting: Material Development and Process Modelling

• Applicants: Professor Dr.-Ing. Hans Jürgen Maier; Professor Dr.-Ing. Ludger Overmeyer
• Subject Area: Synthesis and Properties of Functional Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins ; Production Automation and Assembly Technology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 409485213

In the first funding period, a new approach to improve the processability of magnesium (Mg) alloys by laser powder bed fusion (PBF-LB) has been successfully established by adapting the oxidation behaviour of the Mg alloy itself. As intended, less laser energy is required in order to break the oxide layer of the powder particles made of the new magnesium-strontium (Mg-Sr) based alloy. In the follow-up project a new, lower-energy laser process will be developed that will lead to much less vaporization of metallic Mg, which is key to finally solving the main issue in the additive manufacturing of Mg powder alloys. Therefore, a newly designed laboratory facility will provide the basis for investigating the processing of new Mg alloys with an extended process window. Variable laser spot sizes and a laser wavelength of 2 μm will allow the melting behaviour of the alloys to be controlled. A hydrogen-enriched process atmosphere will additionally promote processing. The aim of the group at LZH is thus to explore the process environment that will lead to reproducible additive processing of the new Mg-Sr based alloys. At the same time, coaxial process monitoring using a spectrometer is being used to research an innovative form of process control that is intended to predict component properties and process defects. Since the element Sr could be employed to effectively reduce the oxide layer thickness, further investigations will focus on the development of highly biocompatible Mg alloys. The elements calcium and zinc are promising for biomedical applications, since they show substantially better resorption by the body as compared to rare earth elements and are commonly used to improve the mechanical properties. The main objective for the group at the IW is to modify the Mg-Sr based alloy with calcium and zinc to create ternary and quaternary alloys that exhibit higher strength while maintaining the beneficial oxidation behaviour. Calcium will increase the strength but also the corrosion rate, if its content exceeds 0.5 wt.-%. Hence, further adaptations will be made by using zinc, which opens up new paths to adjusting the properties since the rapidly cooled PBF-LB components are usually far from thermodynamic equilibrium. Thus, suitable heat treatments will be developed to tailor the grain size as well as the second phases inside the microstructure. The new material concept will then be validated comprehensively using static and cyclic mechanical testing combined with in vitro corrosion measurements. The mechanisms involved will be investigated in situ be means of tomographic analyses as well as detailed microstructure analysis using SEM-EDX, FIB and XRD. With the knowledge gained, demonstrator parts will be developed. As Mg is – due to its bioresorption – especially suited to manufacture of degradable biomedical implants, one of the demonstrator parts will mimic an implant for osteosynthesis.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2122: Materials for Additive Manufacturing