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

Precipitation processes in an industrial Al-Mn-Mg-Cu alloy have been monitored using thermoelectric power and resistivity measurements. Using both techniques it is possible to separate effects due to Mg/Cu and Mn/Fe precipitation, and to calculate the weight percentage precipitated during each process. It is found that Al2MgCu precipitates form at annealing temperatures below 225 degrees C. At these temperatures a maximum of 0.25 wt% of each element precipitates. For this type of precipitation the dislocation density prior to annealing has no significant effect on the precipitation kinetics. precipitation of Mn occurs at temperatures above 225 degrees C and a maximum of 0.48 wt% precipitates. In contrast to Mg/Cu precipitation, the dislocation density and annealing temperature both exert a significant influence on the Mn/Fe precipitation kinetics. Only a very small amount of Mg2Si phase was found to precipitate. Based on the experimental evidence it is likely that Al2MgCu precipitation on dislocations is favored by annealing at temperatures below 300 degrees C whilst Mn bearing precipitates form at dislocations after short annealing times at 500 degrees C.