Abstract
The present investigation examined thickness ranges and conditions to form the super-saturated solid solution and the equilibrium phase in Al-3% Mn alloy, which had a strong tendency to produce the supersaturated solid solution and remarkable section-sensitivity, by means of rapid cooling in various solidification conditions. Then the experimental procedures used were measurements of micro-vickers hardness and lattice parameter, thermal analysis and microscopic observation. The results obtained were as follows:
(1) The structural diagram of Al-3% Mn alloy concerning the average solidification rate was established from the changes of hardness and lattice parameter for the thickness up to 8 mm.
(2) The minimum solidification rate d(Δε)⁄dt required to form each solidified structure was 4.9×10−2 cm/sec, 1.5×10−2 cm/sec, and 1.0×10−2 cm/sec for the completely super-saturated solid solution, the incompletely super-saturated solid solution and the primary compound+eutectic phase, respectively.
(3) Assuming the solidification model of hexagonal array in the solid-liquid region for the supersaturated solid solution, the solid fraction fs(D0,θ) was proportional to the time θ=(t−ti) at a constant thickness D0. At a constant time t0, the solid fraction curve fs(D,t0) showed such curves as being d2fs⁄dD2>0 for the incompletely super-saturated solid solution and d2fs⁄dD2<0 for the completely super-saturated solid solution.
