Monitoring the precipitation reactions in a cold-rolled Al-Mn-Mg-Cu alloy using thermoelectric power and electrical resistivity measurements

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.