Materials characterization by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was performed using a JEOL-JSM-6000 operating at 15 kV in order to verify the Alclad 7075 cladding, core, and corrosion product elemental analysis (i.e., red corrosion product containing 7.71 mass% Cu).
Upon visual inspection of the Alclad medium scale test panel, shallow irregularly shaped corrosion patches are fairly evenly distributed over the panel surface.
Five distinct regions of corrosion behavior were observed: (1) The surface of the clad spots experienced general corrosion, where the Alclad layer was depleted as a sacrificial anode, protecting the overall panel surface.
Figure 3 shows one of the large corrosion patches distributed over the Alclad test panel surface.
From the visual observations and representative cross sections of the medium scale test panels, it is apparent that the cladding layer of the Alclad test panel successfully protected the high strength aluminum core from the corrosion environment.
From the tensile strength results, the partially clad test panel had the smallest reduction in tensile strength after corrosion exposure with a percent decrease of 3.4% while the Alclad and bare panels had percent decreases of 4.0% and 5.3%, respectively.
In this instance, the Alclad test panel outperformed the partially clad test panel but the partially clad panel performed much better than the bare panel.