This study was made on the content of iron in solid solution, the amount and type of intermetallic phases in Al-Fe alloys solidified in a wide range of cooling rate. Al-0.04%Fe, Al-0.10%Fe, Al-0.25%Fe, Al-0.55%Fe, Al0.10%Fe-0.04%Si and Al-0.55%Fe-0.12%Si alloys were cast into a wedge-shaped aluminum mould, a castiron mould and as and mould. Thus a wide range of cooling rate during solidification could be obtained. The measurements of cooling rate, dendrite arm spacing, iron content in solid solution and identification of secondary constituents were carried out by thermal analysis, electric resistometry, optical microscopy, electron microscopy and X-ray diffraction. The dendrite arm spacing in the ingots cast by several industrial casting processes were also measured.
The results obtained are summarized as follows:
(1) The relation between the dendrite arm spacing D(μm)and the cooling rate C (°C/sec) was determined as D×C^0.33=33.4
(2) As cooling rate increased the content of iron in solid solution increased. At a constant cooling rate, increasing addition of iron increased supersaturation of iron in solid solution.
(3) Supersaturation of iron was reduced by addition of silicon.
(4) Al₃Fe, Al₆Fe and Al_mFe (a new body-centered tetragonal Al-Fe phases⁶⁾) were identified as secondary constituents. These were found to be formed in the following ranges of cooling rate:
Al₃Fe: less than 1°C/sec
Al₆Fe: from 1 to 10°C/sec
bct AlmFe: more than 10°C/sec.
(5) By using the above relation, cooling rates for several industrial casting processes were estimated:
200-700°C/sec for Hunter engineering process
20-80°C/sec for pressure die casting
0.5-20°C/sec for D. C. cast
0.5-13°C/sec for Properzi process
0.1°C/sec for book mould casting
0.01°C/sec for shell mould casting.
Estimation of iron content in solid solution and existing intermetallic compounds could be also made for Al-Fe alloys cast by these casting processes.