The morphology and growth kinetics of the cellular precipitate as well
as its discontinuous coarsening have been studied in the temperature
range 440-580 K. Optical microscopy and X-ray diffraction were used to
characterize the cellular transformation. A rapidly solidified metast
able Mg-7 at.% Al alloy was observed to decompose completely via a pro
cess which has been termed ''cellular precipitation'' into a lamellar
structure consisting of the delta and gamma phases al all aging temper
atures used in this investigation. The fine lamellar structure of the
primary cells subsequently decomposed into a coarse lamellar structure
consisting of the same two phases, Lattice parameter measurements hav
e indicated that the depleted matrix of the delta phase associated wit
h the initial cells was richer in solute than the equilibrium solvus,
delta/(delta+gamma) The solute concentration in the depleted matrix as
sociated with the coarsened material was less than the published equil
ibrium solvus. Analysis of the growth kinetics of both the primary cel
lular reaction, and its subsequent coarsening stage, has indicated tha
t the transformation is controlled by diffusion of aluminum through th
e cell boundaries.