Development of various microstructures by Friction Stir Processing to modify deeply the corrosion behavior and biodegradability of Mg-2%Ca alloy
By Corentin Velard (UCLouvain & SIMAP-LEPMI, Grenoble INP), Aude Simar (UCLouvain), Jean-jacques Blandin (SIMAP, Grenoble INP), Emilie Ferrie (SIMAP, Grenoble INP), Virginie Roche (LEPMI, Grenoble INP. Université Savoie Mont Blanc, CNRS)

Bone fractures sometimes require the use of temporary reconstruction implants. To avoid various problems, especially concerning the removal surgery, bio-resorbable materials are investigated. Correct bio-resorption requires controlled dissolution rates of the implant.
In this context, this study involves the development of Mg-2%Ca alloy with controlled microstructures to obtain adjustable dissolution kinetics. Strong variation in the dissolution kinetics requires strong variation of the microstructure, which is obtained using Friction Stir Processing.
The impact of Friction Stir Processing (FSP) on the corrosion of the alloy was investigated. The intermetallic phase Mg2Ca present in the alloy seems to play a major role on the corrosion behavior of the Mg-2%Ca alloy. The distribution of the second phase Mg2Ca in the α-Mg phase turns out to have a great influence on the corrosion rate and we confirmed that a continuous network promotes deep corrosion that leads to significant and quick degradation. The FSP process breaks and redistributes the intermetallic phase. This distribution largely modifies the corrosion resistance of the alloy. Furthermore, FSP can greatly reduce the grain size, which results in a modification in corrosion resistance.
Distinct microstructures have been generated using several sets of FSP parameters. One developed microstructure, very different from the base alloy, was particularly interesting as confirmed by electrochemical characterizations and mass loss measurements. The other microstructures studied help to better understand the relationship between microstructural features and corrosion resistance of the Mg-2%Ca alloy.
These results show major microstructural key parameters to control corrosion resistance and therefore the rate of degradation of the Mg-2%Ca alloy.