Abstract
Defects identified as bubbles and fissures were found in aluminium components used in internal combustion engines forged from flat extruded bars. Samples exhibiting these features were sectioned and prepared for microstructural characterization using light optical and scanning electron microscopy. The analyses were also conducted in samples that did not have such defects for comparison. The bubbles revealed the presence of oxidation and carbon residues in their interior and a series of cracks that developed from them. The fractured surface of the cracked samples revealed the presence of similar residues. The study was complemented with metallographic observations on samples cut from extruded bars from which the components were forged to identify the origin of the defects in forged pieces. These studies revealed the presence of cracks and voids close to the surface of the extruded bars. Therefore, it was concluded that the bubbles and cracks originated from the lubricant used in forging trapped within the voids and cracks of the extruded bars. The lubricant will volatilize and expand in such a case, causing bubbles and cracks in the forged components. The analyses conducted to the establishment of a quality criterion for acceptance of extruded bars.
Published Version
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