Abstract
The microstructure and solidification behaviour of an Al-Mg alloy with different Mn additions have been investigated using optical microscopy and an electron microprobe. The results showed that small additions of Mn had little influence on the solidification behaviour. The microstructure consisted of primary alpha-Al dendrites, the binary eutectic compound Al8Mg5, and the insoluble constitutents Mg2Si and Al-6(Mn,Fe). In the alloy with an intermediate level of Mn, after the eutectic reaction L-->alpha-Al+Al-6(Mn,Fe), the balance of Mn atoms further segregated to the finally solidified zone and formed platelike Al-6(Mn,Fe). In the alloys with the highest level of Mn, the primary phase became Al-6(Mn,Fe) with a block or 'Chinese script' structure. However, the finally solidified zones could be regarded as the binary Al-Mg system, and solidification terminated with the eutectic reaction L-->alpha-Al+Al8Mg5. In addition, the cooling rate had a remarkable influence on the solidification behaviour and microstructure. (C) 1996 The Institute of Materials.
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