Surface Characteristics and Corrosion Behavior of Wire Electrical Discharge Machining Processed Mg-4Zn Alloy

Abstract

In the present work, wire electrical discharge machining (WEDM) has been investigated for surface characteristics and corrosion behavior of Mg-4Zn alloy. Using Taguchi’s design of experiment technique, the influence of WEDM parameters, namely spark-on time, spark-off time, and servo voltage, has been studied on surface roughness (SR) and corrosion rate (CR). SEM observations showed that WEDM processing has a significant influence on the surface modification of Mg-4Zn alloy. Increasing discharge energy in the WEDM process has resulted in large surface craters, a higher density of micro-cracks, and micropores resulting in higher SR and accelerated CR in Mg-4Zn alloy. Corresponding to minimum SR and CR, the optimal set of WEDM parameters has been selected to prepare the WEDMed Mg-4Zn samples that were further analyzed for electrochemical polarization, apatite formation, and weight loss in simulated body fluid (SBF) and were additionally compared to polished samples of Mg-4Zn over a period of 21 days. Electrochemical polarization tests demonstrate that the CR increases rapidly upon the exposure time of 7 days; beyond that, the CR decreases with further exposure time up to 21 days. Initially, up to 24 hours, WEDMed samples showed better electrochemical corrosion resistance, whereas, later on, polished samples demonstrated an increased corrosion resistance for up to 21 days. Higher mineralization (or apatite formation) has been observed on WEDMed samples, which directly affects the amount of Mg ions released into the SBF solution; thus, weight loss was higher in the WEDMed sample than the polished sample. The weight loss for polished and WEDMed Mg-alloy samples after 21 days of immersion test was 9.3% and 13.5%, respectively. SEM analysis revealed the distinct corrosion morphology among the corroded surface of polished and WEDMed samples.