Optimization on the electrical discharge machining (EDM) process parameters of aged AA7075/TiC metal matrix composites

Abstract

The need to optimize the process parameters in Electrical Discharge Machining (EDM) for aged AA7075 Metal Matrix Composites (AAMMCs) is evident as it impacts various aspects such as mechanical properties, tool wear, surface finish, integrity, precision, accuracy, process stability, process consistency, and cost-effectiveness. In this study, aluminium alloy AA7075 was chosen as the matrix material because of the need to enhance its mechanical properties. Titanium Carbide (TiC) was chosen as the reinforcing material owing to its superior mechanical properties. Therefore, TiC holds the capability to improve the mechanical attributes of AA7075. The selection of the stir cast method for the manufacturing of AA7075/TiC (0, 4, 8, 12, and 16 wt.%) was based on its ease of fabrication, ability to achieve a uniform distribution of reinforcements, reduced susceptibility to oxidation and porosity, and improved control over the microstructure. This AA7075/12wt.%TiC MMC underwent an aging process at 520 °C for 180 min and was subsequently cooled within the furnace environment. The density of the aged and non-aged AA7075/TiC-based composites was determined through a density test using the Archimedes’ principle. Microhardness testing was conducted on the non-aged and aged AA7075-based MMCs employing a Vickers microhardness tester. Tensile strength and compressive strength of the aged and non-aged AA7075-based MMCs were determined by the usage of a universal testing machine (UTM) and a compression testing machine (CTM). The optimal combination of the manufactured AA7075/TiC MMCs was determined based on their mechanical properties. The most effective combination was identified as AA7075/12wt.%TiC MMC due to its superior values in hardness, tensile strength, compressive strength, and density compared to other combinations. The aging process aimed to enhance the mechanical properties without the need for additional reinforcements. EDAX and X-ray Diffraction Analysis (XRD) tests were employed to determine the weight percentage of the matrix and reinforcements and to identify the formation of precipitates in the AA7075/12wt.%TiC composites. The SEM equipment was utilized to verify the uniform distribution of titanium carbide in the matrix material AA7075. Optimization of EDM process parameters for aged AA7075/12wt.%TiC composite was carried out using Taguchi design-based Grey Relational Analysis (GRA). The selected input parameters for the optimization included the chromium concentration (g×l-1), current (amps) and pulse-on time (µs). The response parameters chosen for optimization were surface roughness (SR) and tool wear rate (TWR). The sequence of influencing EDM input parameters is chromium concentration, pulse on time and current. The optimized EDM process parameters were 8 g×l-1 chromium concentration, 5 amps current and 240 µs pulse on time and the corresponding response were 0.198 TWR and 1.56 SR.