Surface Modification of Biodegradable Mg-4Zn Alloy Using PMEDM: An Experimental Investigation, Optimization and Corrosion Analysis - 16/02/21

Doi : 10.1016/j.irbm.2021.02.003

G. Sharma ^a, K. Kumar ^a, P.S. Satsangi ^a, N. Sharma ^b,^{^⁎}
^a Department of Mechanical Engineering, Punjab Engineering College, Chandigarh-160012, India
^b Department of Mechanical Engineering, Maharishi Markandeshwar (Deemed to be University), Mullana-133207, Ambala, India

^⁎Corresponding author.

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Graphical abstract

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Highlights

•	The surface of Mg-4Zn Mg alloy is successfully alloyed by PMEDM using Zr and Mn powders.
•	Highest MRR by both the powders is achieved at 4 g/l of powder concentration.
•	At optimized setting, the responses are MRR: 32.14 mm³/min; SR: 5.578 μm and TAL: 8.28 μm.
•	CR of the machined sample at optimum settings is 40.74% lesser as compared to polished sample.

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Abstract

Objectives

Magnesium alloys are the potential candidate for metallic implants due to their excellent mechanical characteristics, biodegradable nature, and properties similar to human bone. However, a high degradation rate is primary obstacle in implementing these alloys as biodegradable orthopedic implants. Powder-mixed electric discharge machining (PMEDM) is an emerging method of surface modification of metallic alloys that can be implemented to improve the corrosion resistance of Mg alloys. Therefore, PMEDM using zirconium (Zr) and manganese (Mn) powder particles has been proposed to modify the surface characteristics of Mg-4Zn alloy.

Materials and Methods

In the present work, Zr and Mn powders have been used in varying concentrations during PMEDM of Mg-4Zn alloy. Experiments were conducted as per mixed design L18 orthogonal array (OA). Taguchi and Grey Relational Analysis (GRA) have been used to optimize the process parameters. Analysis of response characteristics, namely material removal rate (MRR), surface roughness (SR), and thickness of the alloyed layer (TAL), has been carried out at different values of input variables (like powder additives (P_a), powder concentration (C_p), peak current (I_p), pulse on time (T_on) and duty cycle (DC)). The corrosion analysis was carried out by immersing the specimen (machined at an optimized setting) in simulated body fluid (SBF).

Results

It is observed from the analysis that C_p, I_p, and T_on play a pivotal role in evaluating response characteristics. The favorable setting suggested by the gray approach is P_a: Zr; C_p: 2 g/l; I_p: 4A; T_on: 50 μs; DC: 80%, while responses at this setting are confirmed by confirmation experiments with MRR: 32.14 mm³/min; SR: 5.578 μm and TAL: 8.28 μm. The immersion test signifies that the corrosion rate (CR) of PMEDMed sample (3.20 mm/year) is 40.74% lesser than the corrosion rate of polished sample (5.40 mm/year).

Conclusion

Zr powder shows better performance in terms of higher MRR, lower SR and higher TAL as compared to Mn powder during the PMEDM process. The corroded surface of polished sample exhibited larger size micro pits and cracks than the machined sample, which concluded that surface modification of MZ-4Zn alloy via PMEDM is a powerful tool to enhance its corrosion resistance.

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Keywords : Biodegradable, Mg-4Zn alloy, PMEDM, Surface modification, Alloyed layer, Corrosion rate