Abstract
The phenomena defects in the triple junction grain boundaries affect the properties of the microstructure of aluminum alloys. For that purpose the microstructure of the alloy EN AW 6060 on the billet sample cast by DC (Direct Chill) technology was analysed in order to gain insight into the origin and form pores in the final stages of solidification. Mechanisms of solidification shrinkage, thermal contraction and low permeability of interdendritic channels networks were discussed in moment when melt becomes isolated in separate locations forming new structure. Under such conditions, the tensile stress caused by anisotropic thermal contraction of a coherent dendrites network, causing the formation of pores in the corners of the grain boundaries whose morphology is determined by SEM / EDS analysis.
Highlights
Cracks are formed in the final phase of solidification near a solid temperature
The cast structure is formed without porosity if the slip-off and thermal contraction is completely compensated by the melt flow through the dendritic network, and later by a high temperature cracking
For aluminum alloy series 6000, hot cracking tests show the surface of the fracture that is relatively flat with visible free dendrites without distortion, or pits and hot cracks can be described as a result of interdendritic separation [18]
Summary
Non - uniform cooling of the Al billet causes hot cracks and describes the stresses when the thin film melt separates the dendrites somewhat. The resulting cracks grow due to stress concentrations, segregation inclusions, Measurement of hardness on the cross section of the billet, the contours of the results that were associated with the strain stresses were obtained. This macro result has been the cause of the search for micro cracks in the critical part of the billet.. The cast structure is formed without porosity if the slip-off and thermal contraction is completely compensated by the melt flow through the dendritic network, and later by a high temperature cracking. Pores as potential nuclei of hot cracks may come from captured gas, shrinkage during solidification or excessive saturation of cavities (free spots) [6]
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