Effect of powder particle concentration, pulse duration, and pulse current on machined surface characterization produced via EDM of biocompatible WE-43Mg alloy

Abstract

Magnesium alloys are being explored as biodegradable metal alloys for implant applications because of their analogous engineering properties with human bones such as Young's modulus and density. Conventional machining of biodegradable Mg alloys is challenging due to low melting point (650 °C), occurrence of chatter, built-up edge (BUE) formation, poor surface finish, and low dimensional accuracies. Among non-conventional machining methods, Electric Discharge machining (EDM) is the most popular material removal technique because of its ability to handle the temperature issues related to Mg alloys due to the presence of dielectric and can generate 3D complicated intricate shapes with tighter tolerances. In addition, the powder-mixed variant of the EDM process possesses the unique capability of producing machined surfaces comprising of oxides and carbides which in turn improves the biocompatibility of metallic implants. Moreover, EDMed surfaces have greater hardness and better wear and corrosion resistance. In the current work, Mg-WE43 alloy was machined via die-sinking EDM process by varying SiC powder concentrations (Cp) (2, 4, 6 g/l) together with the variation in pulse current (5, 7, and 9 A) and pulse-on-time (50, 75 and 100 µs). To understand the surface characterization, machined surfaces were examined by measuring the surface roughness and re-cast layer thickness as output responses. Furthermore, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to analyze the formation of oxides and carbides on the machined surfaces. A minimum surface roughness of 2.70 μm was obtained at 2 g/l powder particle concentration (Cp), 50 µs pulse-on-time (Ton), and 7 A pulse current (Ip) with a re-cast layer thickness (RLT) of 31.318 μm while a minimum recast layer of thickness 28.20 μm was produced at 4 g/1 powder Cp, 5 A Ip, and 50 µs Ton with Ra value of 3 μm. SEM analysis of machined workpieces of both tests revealed shallow craters and smooth surfaces with a uniform distribution of carbides. The latter phenomenon was also confirmed by Energy Dispersive Analysis (EDS) executed on machined surfaces.