Si. Vooijs et al., Monitoring the precipitation reactions in a cold-rolled Al-Mn-Mg-Cu alloy using thermoelectric power and electrical resistivity measurements, PHIL MAG A, 81(8), 2001, pp. 2059-2072
The aim of the present paper is to monitor multiple precipitation reactions
in a normal Al alloy AA 3104 and a Mg- and Cu-rich alloy 3104 during isoth
ermal annealing. Special emphasis is placed on the influence of dislocation
s on the precipitation kinetics and therefore different cold-rolling reduct
ions are applied prior to the annealing treatment. Using both thermoelectri
c power (TEP) and electrical resistivity measurements it is possible to spl
it concurrent and sequential precipitation reactions and to reduce the unce
rtainty about the actual precipitation reactions taking place. It is found
that Al2CuMg precipitates form at low annealing temperatures, irrespective
of the extent of pre-deformation. During annealing at temperatures from 350
degreesC and higher, precipitation of Mn-containing dispersoids is determi
ned as the only process occurring. The rate of this precipitation process i
s strongly influenced by the degree of cold work prior to the heat treatmen
t. The qualitative information derived from the combined TEP and electrical
resistivity experiments is supported by transmission electron microscopy o
bservations. It is also possible to calculate the weight fractions of the e
lements precipitated semiquantitatively. These calculated fractions are com
pared with equilibrium thermodynamic data and show good agreement for the p
recipitation of Al2MgCu and the precipitation of Mn at temperatures up to 4
00 degreesC.