The reversion behaviour of an AlCu(1.87) alloy is investigated mainly by microhardness (HV) measurements in dependence on the pre‐ageing temperature (Tpre = RT and 70 °C) and the pre‐ageing time (0 ≦ tpre ≦ 28 d). The following reversion treatment is performed at Trev = 130 °C. The GP‐zones pre‐grown at RT are less stable against reversion at 130 °C in comparison with the storing at 70 °C. The HV‐development significantly depends on the pre‐history of the samples. Recent investigations performed by means of HREM and FIM are used to interpret the quite different results of the measurements.
The structure changes proceeding in an Al–1.87 at% Cu alloy at 100 °C are followed by microcalorimetric, hardness, and small‐angle X‐ray investigations in dependence on both, pre‐ageing tempe rature Tpre (RT and 70 °C) and pre‐ageing time tpre. The most important result is that the GP zones grown at RTare more easily transformed into GP zones able to proceed to grow at 100 °C than those formed at 70 °C. These differences are discussed in terms of the kind of the GP zones present at the end of the pre‐ageing treatment. The reversion behaviour of GP zones grown in AlZn, AlZnMg as well as in AlCu alloys is discussed.
The results of the reversion experiments on Al–1.87 wt% Cu alloys, previously published by the authors, are summarized with the aim to test the different conceptions of reversion. In addition to the hitherto reported results selected two‐ and three‐step‐ageing processes are evaluated, which support the conceptions of the reversion in Al–1.87 wt% Cu alloys. According to the respective results the partial reversion in this alloy exhibits three features, i.e. the two hitherto known mechanisms, viz. the critical nuclear size and the growth, are effectively influenced by a third one. It is attributed to the different possible GPZ structures.
The size distribution of approximately spherical incoherent precipitations of Zn in AlZn‐alloys is calculated and experimentally tested by means of neutron small angle scattering (NSAS) at a double‐crystal diffractometer (DCD). The scattering curves can be approximated by a Gaussian function, so that the size distribution is directly calculated for the experimentical scattering curves under application of a particular LAPLACE‐transformation. The size distributions of the α′m‐phase of AlZn(16)‐samples of different averaged radii of precipitations are calculated by means of FWHM which are determined by the fitting procedure of a computer programme and compared with TEM micrographs.
The decomposition in AlCu and AlCuMg alloys during one‐step ageing is pursued with the experimcntal methods: Vickers hardness measurement, dilatometry, and transmission electronmicroscopy. The results indicate that magnesium accelerates the decomposition and the proportion of thc heterogeneous nucleation is increased. This is mainly caused by the greater loop density. Mg‐containing GPZ(Mg) and θ″(Mg) are formed.
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