Abstract
To evaluate the effect of homogenization conditions on the possible loss of low-melting-point Pb and Bi to the surface in the free-cutting AA6026 alloy, three homogenization regimes were applied: 480 °C/12 h, 530 °C/12 h, and 550 °C/6 h. The microstructural characterization by optical, scanning, and transmission electron microscopy coupled with EDS analysis, macroanalysis of chemical composition by ICP-AES as well tensile tests at room and 500 °C, and Charpy impact test were employed to evaluate the different homogenization regimes. It was found that the choice of homogenization temperature had no significant effect on the level of loss of low-melting point elements. The optimal homogenization regime appeared to be 550 °C/6 h as it led to almost complete β-AlFeSi → α-AlFe(Mn)Si transformation and β-Mg2Si dissolution resulting in improved mechanical properties. The presence of the liquid phase did not lead to catastrophic failure due to the liquid metal embrittlement of the aluminum matrix, but the wetting of Fe,Mn – bearing constituents by molten Pb led to decohesion of the constituents. The morphological change to globular α-AlFe(Mn)Si decreased the surface area and interconnectivity of the microconstituents, which improved the hot ductility. During cooling after homogenization at T > 500 °C, the Q-phase precipitated, pointing up the potential quench sensitivity of the alloy. However, precipitation of the Q-phase laths in dispersoid-free zones reduced strain localization and improved room temperature ductility and impact toughness.
NSTL
Elsevier