Abstract
The macrostructure of the following aluminium alloys were examined: Al-Ti (Ti<0.16%), Al-Mg (Mg<8.0%), Al-Mg-Ti (Mg<8.0%, Ti<0.16%), Al-Cu (Cu<8.0%), Al-Cu-Ti (Cu<8.0%, Ti<0.16%), Al-Zn (Zn<8.0%) and Al-Zn-Ti (Zn<8.0%, Ti<0.16%).
The purity of aluminium used as the basis was 99.99% and 99.5%. The specimens were prepared under different conditions: one was cast in a specially designed asbestos mould for making it solidified directionally, and another was cast in an ordinary metallic mould.
Through this experiment, the macrostructure diagrams were established as shown in Fig. 3, 4 and 5.
The findings are as follows:
The macrostructure diagram for specimens of directional solidification consists of three regions; columnar crystals, "Fiederkristall" in columnar crystals and granular crystals. In the case of using 99.5% aluminium the region of granular crystals is wider than in the case of 99.99% aluminium. Diagram for specimens of solidification in a metallic mould also consists of three regions: columnar crystals, mixture of columnar and granular crystals and granular crystals. In this case, the region of granular crystals is wider than that in the directional solidification, and "Fiederkristall" does not appear.
The angle between the direction of the tabular crystal, a member of "Fiederkristall, " and the direction of heat flow is, in most cases, less than 20°.
