The schematic diagram in the lower right corner shows a
simplified version of this type 3a system with only one
monotectic reaction, whereas the Al–Sn–Cu system exhibits
three monotectic reactions (Table 1). Only the one at
the lowest temperature, 524 C, is of the same E-type as
the one discussed in the Al–Bi–Zn system and also marked
by the label M in Fig. 5. For an application to Al-rich
alloys this is the most important reaction. A wide range
of alloys, with and without primary liquid demixing, are
affected by this reaction.
Fig. 3. Electron micrograph (BSE) of the sample Al18–Bi32–Zn50
solidified at 1K min1. The demixing of the two liquids, Bi-poor (L0,
dark area) and Bi-rich (L0 0, light area), is obvious even in the solidified
sample.
Fig. 4. Electron micrograph (BSE) of the sample Al18–Bi26–Zn56
solidified at 1K min1, showing a better view of the dark area of Fig. 3,
originally related to Bi-poor L0 melt. The monotectic microstructure is
surrounded by the (Al) crystals solidified prior to the ternary monotectic
reaction.