Quality of surface and subsurface layers after WEDM aluminum alloy 7475-T7351 including analysis of TEM lamella

Wire electrical discharge machining (WEDM) is an unconventional machining method indispensable especially for the aeronautical and automotive industries. In this context, the effective manufacturing of high surface quality components from aluminum alloy 7475-T7351 requires comprehensive knowledge of the applied production procedures. We therefore performed a designed experiment comprising 33 cycles (with systematic alteration of machine setting parameters such as gap voltage, pulse on time, pulse off time, discharge current, and wire feed), enabling us to evaluate systematically the cutting speeds in the relevant samples. The machined areas were subjected to a thorough analysis involving both the surface and the subsurface layers. The actual topography was assessed using a non-contact profiler, and the entire operation concentrated on 12 parameters within the areal, profile, and basic and bearing profile categories. To observe the surface relief, we employed several instruments, including the semi-contact atomic force microscopy (AFM) technique, a digital microscope, and a non-contact 3D profiler. Another major step then consisted in examining the morphology and surface defects, a process suitably complemented with a chemical composition analysis (EDX). The distribution of individual elements within the material was investigated in detail using a lamella, whose subsequent inspection relied on a transmission electron microscope (TEM) as the principal tool. To study the subsurface layer and its defects, we prepared metallographic specimens (cross-sections) of the samples and observed them by means of light and electron microscopes.