On the Influence of the Pre-Ageing Conditions on the Reversion Behaviour of an Al1.87 at% Cu Alloy

Abstract

The reversion behaviour of an AlCu(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.

On the Stability of Metastable Precipitates in an Al–1.87 at% Cu Alloy at Elevated Temperature

“…At T,,, = 160 "C the dissolution of the zones is retarded the more, the larger the zones are and the greater the proportion of the multilayer G P zones, visible from the shift of t~l -,~,~ or t&,,min, respectively. The absence of the plateau a t T p r e = 70 "C and T,,, = 130 "C [15] was already an indication that multilayer These statements confirm the result of Nakamura et al [17], described in the introduction. Their reversion treatment is comparable to ours (1 d/100 "C + 160 "C).…”

“…A resumptive presentation of the opinions of the structure of plate-like precipitates in the A1-Cu system in dependence on the ageing conditions has recently been given in [15]. The nomenclature used in that paper has been adopted for the present article.…”

“…The pre-ageing treatments a t RT and 70 "C are referred to only for comparison. This discussion can be improved taking additionally into account the recently published results about the structure changes proceeding in this alloy during the post-ageing a t 100 and 130 "C [15,19].…”

“…The HV measurements were accomplished as described in [15]. The reversion behaviour of the alloy was also followed by measuring the SAXS intensity I-& curves a t angles E = 28 ranging between 0.1 " and 2.0" in steps of 0.02" by means of a camera of Kratky type using CuK, radiation.…”

“…G P zones of type 11, uithout delay. They are distinguished from GPZ I pairs by consisting of two (or even more) monolayers of Cu, separated from each other by one to three layers of A1 atoms [15]. These GPZ I1 (being, of course, still fully coherent with the ambient matrix) are supposed to be responsible for the HV value a t level 11.…”