Abstract
Investigations on Al‐Zn(3)‐Mg(X) alloys gave the rather surprising result that the migration energies depend on the physical quantities (resistivity, Young's modulus) and the ageing time used. Therefore it is the aim of this paper to test, if similar effects occur using other ternary alloys and additional measuring methods. The ageing kinetics of 7 Al‐Zn(6)‐Mg(X) alloys are examined by isothermal measurements of resistivity, Young's modulus, change of length, and microhardness over a relatively long time interval of about 3 h within the temperature range from 20°C to 90°C.
The activation energies got for the Al‐ZN(6)‐Mg(X) alloys depend on the physical quantity as well as on the ageing time used within the temperature range from 20°C to 40°C as known from the Al‐Zn(3)‐Mg(X) alloys.
The activation energies obtained for the Al‐Zn(6)‐Mg(1.3) alloy in the temperature interval from 50°C to 90°C decrease monotonously with increasing time for the measuring methods considered.
These results different with respect to those two temperatur ranges are probably caused by a change of the decomposition mechanism. Below 40°C presumably several kinds of clusters are formed in the beginning of the decomposition, but above 50°C probably only one sort of clusters should grow. The late stage of ageing should be caused mainly by the diffusion of VZn~2~ complexes (E^M^ = 0.21 eV) in the temperature range investigated, since 0.2 eV holds for that stage. – Finally the results of the investigations of the kinetics of some Al‐Mg(X)‐Si(Y) alloys are discussed by means of the jump model.