Study the effect of electrical discharge machining (EDM) on residual stress and corrosion resistance of Ti-6Al-4V alloy

Ti-6Al-4V alloy due to excellent mechanical properties mainly is used in the aerospace, automobile and biomedical industries. Electrical discharge machining (EDM) are used extensively for machining of this alloy. Due to the thermoelectric nature of this process, unwanted changes happen on machined surface such as development of residual stresses and the change in the corrosion resistance. The aim of this study is the experimental investigation of the effect of input parameters (discharge current and pulse on time) on the amount and distribution of residual stresses and corrosion resistance changes of the machined surface in EDM process of Ti-6Al-4V alloy. For this purpose, samples of Ti-6Al-4V alloy were machined by EDM process and residual stresses induced successive sparks in different setting (different discharge currents and pulses on time) were measured by nanoindentation method and SEM images of machined surface used to better assess of samples surface integrity. TOFL measurement method used to determine the corrosion resistance of the samples. Results indicate that at this process tensile stresses is formed on surface and mentioned stresses increase with depth initially and after reaching a maximum dropping out and eventually leads to pressure stress. By increasing pulse on time and discharge current, maximum tension residual stress only slightly increases and is near ultimate tensile strength of work piece material. Comparison of corrosion results indicated that the corrosion resistance of EDMed samples, was less than the not machined specimens.