Citation: Abbas, A.; Huang, S.-J. Investigating the Synergic Effects of WS 2 and ECAP on Degradation Behavior of AZ91 Magnesium Alloy. Coatings 2022, 12, 1710. https:// doi.org/10.3390/coatings12111710 Academic Editor: Alina Vladescu Received: 4 September 2022 Accepted: 24 October 2022 Published: 9 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). coatings Article Investigating the Synergic Effects of WS 2 and ECAP on Degradation Behavior of AZ91 Magnesium Alloy Aqeel Abbas 1 and Song-Jeng Huang 2, * 1 Interdisciplanary Research Center, King Fahad University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia 2 Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan * Correspondence: sgjghuang@mail.ntust.edu.tw Abstract: In this research, WS 2 /AZ91 metal matrix composites were manufactured using the stir casting method. The composites were severely deformed using equal channel angular pressing (ECAP). The degradation behavior of severely deformed and as-cast samples was investigated using the three-electrode system in a 3.5 wt% NaCl solution. The corrosion products and surface morphology of the corroded surfaces were investigated using an x-ray diffractometer and scanning electron microscopy. The results revealed that as-cast monolithic AZ91 exhibited the highest corrosion potential of (−1.553 mV) and a minimum degradation rate (4.099 m·a −1 ). The reduction ion grain size after severe plastic deformation increased the degradability of WS 2 /AZ91 composites. Severe plastic deformation reduced the grain size, which led to an increase in the corrosion rate. The synergic effects of (tungsten disulfide) WS 2 and ECAP increased the degradation rate to (4.59 m·a −1 ) in two-pass 1 wt% WS 2 /AZ91. The increase in WS 2 contents decreased the degradation rate (4.512 m·a −1 ) in homogenized 1 wt% WS 2 /AZ91 composites. The degradability of AZ91 increased in all conditions under the synergic effects of WS 2 and severe plastic deformation. Magnesium and magnesium hydroxide were observed as corrosion products. The maximum surface roughness in two-pass 1 wt% WS 2 /AZ91 indicated the highest material removed by corrosion from the surface of the composites. Keywords: WS 2 /AZ91; degradation/corrosion behavior; ECAP; Tafel curves; potentiodynamic polarization 1. Introduction Magnesium is one of the lightest structural metals and can replace conventional alu- minum alloys in the automotive and aerospace industries [1]. Magnesium alloys have a low density, high specific rigidity, and excellent electromagnetic shielding performance [2]. Magnesium is a biocompatible material and has many applications in biomedical implants. The degradable behavior and biocompatibility of magnesium make it most suitable for biomedical application in order to avoid second surgery [3]. It requires certain mechanical properties and controlled degradation properties for effective use in biomedical applica- tions. However, a poor corrosion resistance and less specific strength of magnesium alloys have become a bottleneck that restrict their applications [4]. The degradation behavior and specific strength of the magnesium can be controlled by the development of metal matrix composites [5]. The reinforcement type, composition, dispersion, and secondary phases produced have significant effects on controlling the degradation behavior of the magnesium-based metal matrix composites [6]. The reinforcement additives in magnesium play a comprehensive role in forming the solid solution of intermetallic compounds to protect from oxides. The addition of ceramics, aluminum, SiC, V, Ag, Ni, and Zn are the major elements used to improve magnesium’s corrosion resistance [7]. The severe plastic deformation and heat treatment alter the microstructure, which consequently affects Coatings 2022, 12, 1710. https://doi.org/10.3390/coatings12111710 https://www.mdpi.com/journal/coatings