zone suggest the increase of the twinning frequency [4] (Fig.3a). A banded structure occurs in the 
longitudinal section (parallel to the growth axis), always well aligned in the growth direction of the in- 
vestigated samples (Fig.3b). 
The precipitation free zones but of the disordered distribution also occur in the microstructure of 
the samples solidified at the lower growth rate (2.78 um/s) (Fig.3c). The density of the Si-precipitates 
is much smaller than in the samples solidified at the higher rate. The alignment of the precipitates 
along the growth direction on the longitudinal section in the alloy solidified at the lower rate is much 
worse than in the alloy solidified at the higher one (Fig.3d). The interflake spacing A is inversely pro- 
portional to the growth rate change, and the A value ( measured as the average from the cross- and 
longitudinal - sections taken in more than 3 places) for the alloy solidified at 2.78 pm/s is 12 pum but for 
the rate 27.8 um/s A = 6 um what is in accordance with the results of papers [9 and 10]. 
The given above dependences of precipitate shapes on growth rate are much easier to observe in 
scanning microscopy microstructures . The diversification of the precipitate density and the difference 
of the interflake spacings is also more dinstinct (Fig. 4 a,b,c,d). Two types of the precipitates: grey or 
bright white appear, preasumably due to their composition, in these microstructures. The investigations 
with EDS method and the elemental mapping of the distribution of the Al,Si,Fe and Mn (Fig.5 a,b,c,d,) 
in the alloy solidified at the higher rate and in Fig.6. a,b,c,d, for the lower one proved it to be right. Ac- 
cording to spectroscopic measurements, the composition of these phases solidified at 27.8mm/s is: 
bright phase has 64.0% Al, 12.5% Si, 4.46% Mn and 18.3% Fe, the grey phase is built of 98% Si and 2% 
Al while the matrix of 98.15% Al, 1.85% Si. 
+ In the alloy solidified at 2.78 um/s the grey phase is buil nearly of pure silicon - 99.68% Si and 
only. 0.32 Al, the bright phase of 56.64% Al, 16.40% Si, 5.06% Mn and 15.2% Fe and the matrix 
98.35% Al, 1.65% Si. From spectroscopic results it is to see, that the Al - matrix and Si - reinforcing 
phases solidified at lower rate contain smaller contributions as the phases solidified at the higher one. 
4. Conclusions 
1. The preferred orientation of both phases of the investigated alloy solidified at two different rates was 
found to be nearly of the same type <200>. At the higher rate the perfection of texture of both phases 
increases and the deviation of the growth direction from <200> crystallographic direction 
diminishes. 
2. The composition of the phases solidified at the higher rate differs from these formed at the lower one. 
At the higher rate, the silicon precipitates ( grey phase) and Al-matrix contain more Al and Si re- 
spectively, while the bright phase contains them in smaller amounts than these in the samples soli- 
dified at lower rates. 
3 The interflake spacing diminishes with increasing growth rate and their values are in a good agree- 
ment with these given by [4 and 5]. 
Acknowledgement. 
Financial support by grant No 7 S201 07406 from the State Committee for Scientific Research is 
gratefully acknowledged. 
S. References. 
[1]. P.Magnin, J.T. Mason,R, Triverdi, Acta metall. mater. 39(1991)469 
[2]. Shu-Zu-Lu, A Hellawell,J.Cryst. Growth 73(1985)316 
[3]. R Elliott, S.M.Glenister, Acta Met. 28(1980)1489 
[4]. H.A H.Steen, A Hellawell, Acta Met. 20(1970)363 
[5]. B.Touloui, A. Hellawell, Acta Met. 24(1976)565 
[6]. M.G.Day, Iron and Steel Inst,Publ. 110(1968)117 
[7]. O.A Atasoy, F.Yilmaz, R Elliott, J.Cryst. Growth 66(1984)137 
[8]. H.A.H.Steen, A Hellawell, Acta Met. 23(1975)522 
[9]. M.Shamzuzzoha, L.M.Hogan, J.Cryst. Growth 82(1987)598 
[10].K Kobayashi, P.H. Shingu, R.Ozaki, J.Mater.Sci.10 (1975) 290 
564  Prakt. Met. Sonderbd. 26 (1995)