An Experimental and Theoretical Study of the Microsegregation in Al-6Cu and Al-2Si Alloys

摘要

The alloys Al-6%Cu and Al-2%Si were cooled in a DTA furnace at 4K/min (0.067K/s). Three samples of each alloy quenched at different stages during the solidification were studied. Primary dendrite trunks formed in the beginning of the solidification was examined using microprobe analysis. The minimum concentration in the centre of the dendrites was found to be higher than expected taking "back-diffusion" into account. The fraction primary solid and eutectic/quench structure was also measured and found not to be between the upper and lower bounds given by the lever rule and the Scheil equation. It was proposed that these observations could be explained by lattice defects formed at the solid/liquid interface. Kinetic phase diagrams with different amounts of vacancies was drawn and used as a tool in the discussion.