Mechanical and corrosion characteristics of micro-arc oxidized magnesium alloy (ZE41) friction stir welds in modified SBF

Abstract

Abstract Magnesium is a popularly known class of biodegradable metallic biomaterials, and it has spent most of its time in corrosion environments that must be validated before it can be used in real bio applications. This work studies the adaptability of rare earth magnesium alloy (Mg-RE) ZE41 welds for in vitro bio applications. Magnesium rare earth ZE41 alloy plates were welded through a friction stir joining process. The fabrication of a defect-free and strong friction stir butt joint was confirmed by microscopic analysis and mechanical tests. The joint efficiency of 79.25% was arrived from the tensile test based on ultimate tensile strength (UTS). The microhardness at WN, HAZ and base material were measured as 82, 63, and 70 respectively. A silicate electrolyte-based micro-arc oxidation (MAO) coating process was carried out on base and weld samples to study the corrosion behaviour of uncoated and coated samples in modified simulated body fluid (m-SBF). The average coating thickness of the samples was 40 μm. Then the processed samples were immersed in the m-SBF solution for 0.25 h, 72 h, and 168 h, and the degradation behaviour of all the samples was studied. The surface morphology and compositions were analysed through x-ray diffraction and field emission scanning electron microscopy (FE-SEM) on all the MAO-coated and uncoated bases as well as weld samples. The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation (PDP) tests were employed to evaluate the electro-chemical induced corrosion behaviour of the samples. The results revealed that MAO-coated ZE41 welded samples have better corrosion mitigation properties with a corrosion rate of 12.45 mpy after 168 h of immersion than all other counterparts due to the compact oxide layer formation and further apatite mineral phase deposition that helps to delay the surface degradation of friction stir welded ZE41.