# High-pressure torsion of biodegradable Mg−Zn−Mn alloy and investigate mechanical and corrosion behaviour

## TL;DR

This paper shows that high-pressure torsion improves the mechanical and corrosion properties of a biodegradable magnesium alloy, making it more suitable for medical implants.

## Contribution

The novel contribution is demonstrating how HPT enhances corrosion resistance and microhardness in Mg-Zn-Mn alloys through microstructural refinement.

## Key findings

- HPT increased microhardness from 68 Hv to 222 Hv in Mg-Zn-Mn alloy.
- Corrosion rate decreased significantly from 0.0243 mm/y to 0.0012 mm/y after HPT processing.
- The alloy showed good cytocompatibility with MG-63 osteoblast-like cells.

## Abstract

Considering their biodegradability in physiological environments and similar elastic modulus to natural bone, magnesium alloys have generated a lot of interest as biodegradable implant materials. Their poor corrosion resistance is primarily a result of the inhomogeneous distribution of their second phase, which limits their clinical application. High pressure torsion (HPT) one of the severe plastic deformation techniques which provides an opportunity to process materials with low formability such as magnesium at room temperature. The present study HPT is conducted for Mg-Zn-Mn alloy up to ten revolutions at room temperature. Optical, scanning, and transmission electron microscopes were used to examine the microstructures of base material (BM) and ten revolution HPT samples. Significant microhardness improvement was observed in HPT N10 samples (222 Hv) as compared to BM samples (68 Hv). It was determined that the improvement in microhardness was primarily due to dislocation strengthening, fine grain strengthening, and second phase strengthening. Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) were used in a simulated body fluid (SBF) solution to assess the corrosion behaviour. When compared to the BM sample (0.0243 mm/y), the corrosion resistance of the HPT N10 sample (0.0012 mm/y) increased significantly. This was mostly due to the smaller grain size and uniform dispersion of the secondary phases, which result in a uniform corrosion. Further, obtained data from the cytotoxicity assay carried out using the MTT method indicated the compatibility of the Mg-Zn-Mn alloy on MG-63 osteoblast-like cells, further substantiating its safety on the bone cells.