Coarsening of S'-Al_2CuMg in AI-Cu-Mg base alloys

摘要

An earlier contribution [1] reviewed and assessed the available experimental data on coarsening of pre-cipitates and dispersoids in aluminium-based sys-tems. This included data on Cu-containing phases such as Θ, Θ', Θ", S', T1, and Ω. Results from different workers for Θ', Θ", T1 and Ω were in reasonable mutual accord whereas results for S' were not mutually consistent. In summary, the results of Christman and Suresh [2] for Al-4Cu-2Mg-0.5Mn at 177 °C gave KT values similar to Ti in Al-Cu-Li-Zr, while those of Cho [3] for Al-2Cu-lMg at 200 and 230 °C gave KT values two orders of magnitude less, similar to the lowest values meas-ured for δ'-Al3Li in Al-Li base alloys at these temperatures. (K = (r3 - r30/t), where r0 is initial radius and r is the value at time /.) A measurement by Ahmad and Eriksson [4] for Al-2.5Li-l.2Cu-0.7Mg-0.1Zr at 190 °C gave a value of KT some five orders of magnitude less than that measured by Christman and Suresh for Al-4Cu-2Mg-0.5Mn. The present purpose is to report that data in an earlier paper by Sen and West [5], which has since come to our attention, helps to clarify the situation. Their data for coarsening of S laths in Al—3.3Cu-1.6Mg and Al-3.2Cu-l.5Mg-0.5Ag alloys are given in Table I and Fig. 1 together with the more recent data. Fig. 1 shows that the results of Sen and West lie somewhat below those of Cho for his more dilute alloy and well below the results of Christman and Suresh for their more concentrated alloy. Sen and West's values of KT are in fact among the lowest values reported for Cu-containing phases in Al base alloys, comparable with Ahmad and Eriksson's result for S' in a Li-containing alloy (AA8090) at 190 °C and Janoff and Fine's result [6] for Θ-Al2Cu in Al-6Cu at 450 °C (allowing for the differences in temperature).