Analysis of permeability of interdendritic channels during solidification of aluminum magnesium alloys

Purpose: The knowledge of the variation of permeability in interdendritic channels is important in order to analyze the ability of the liquid flow compensate the shrinkage of the alloy during solidification. In this work the influence of the magnesium content in the permeability of interdendritic channels during unidirectional solidification of Al-Mg alloys is analyzed. Design/methodology/approach: Al-Mg alloys with 5, 10 and 15 wt% Mg were submitted to unidirectional solidification leading to a columnar dendritic structure. From the samples obtained, the primary and secondary dendrite arms spacing variations during the solidification process were measured. Applying a heuristic method, developed by some of the authors of this work, the variation of permeability of interdendritic channels for a flow parallel to primary dendrite arms was estimated as function of primary and secondary dendrite arms spacing, and liquid fraction variations during solidification. Findings: From the results obtained for the three alloys with different compositions it was concluded that the behavior of the permeability depends on the relation between secondary and primary dendrite arms spacing and for the same distance from the metal/mould interface the permeability decreases when the magnesium content increase. Research limitations/implications: The magnesium content affects the primary and secondary dendrite arms spacing affecting as consequence the permeability of the interdendritic channels. Both primary and secondary dendrite arm spacing increases with magnesium content. The permeability depends on primary and secondary dendrite arm spacing, but also on the relation between these parameters. Originality/value: It was concluded that, for Al-Mg alloys, the permeability of interdendritic channels decreases as magnesium content increases, indicating that the probability of microporosity formation increases for greater magnesium content.