Abstract: Effect of forward extrusion distortion on the anodic layers formed in sulfuric acid on LC4CS alloy bars is studied. The microstructure of the substrates is assessed by optical microscopy (OM). The surface and crosssection morphologies of oxide layers are examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The oxide layers developed a microscale topography which is determined by the morphology of the extrusion bar substrates. Preferential dissolution of second phase particles containing copper or magnesium leads to cavity defects of the layers, and insoluble impurities tend to be occluded in oxide layers whenever the particles are present in the substrate/oxide interface. Preferential dissolution of cracked particle chains forms during extrusion is the main reason of pits in oxide layers and the scalloped substrate/oxide interface. The netlike structure of the layers is caused by grain or subgrain boundaries in the incompletely recrystallized alloy substrate.

Key words: anodic oxide, extrusion, intermetallic particles, pits, netlike structure