The segregation of several binary aluminium- magnesium- alloys and some commercial strong Al alloys was fully investigated. The influcene of various factors which affect the extent of segregation and its nature was also thoroughly examined. These factors include : composition of the alloy, casting temperature, cooling rate, mould temperature, & the relative size of ingot to mould etc. The resalts obtuined are shown as follows :
  (1) The nature of segregation, viz., normal or inverse, and its occurrence do not seem to be dependent of the type of the alloy's diagram.
  (2) The segregation-behaviour of the component metals in commercial alloys is almost similar that of in each binary alloy
  (3) As already cited by Masing & Bohner, the nature of segregation depends primarily upon the rate of solidification.
  (4) It is confirmed that one of the most efficient and practical methods, to prevent segregation, is the “layer-by-layer solidifing” process by adequate water-cooling. The “SKS-II” casting method, which is new used at the authors' works is such as this.
  (5) The heavy ingots of SD or 25 S alloy, made by the “SKS-II” process, are proved to be almost all free of segregation.

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