Influence of Cr, Mn, Zr on the Pre-Precipitation in Al-Zn Alloys

Abstract

Experiments have been carried out to investigate the influence of addition of Cr (0.01∼0.2 at%), Mn (0.01∼0.3 at%) and Zr (0.01∼0.2 at%) to Al-2.5 at% (6.0 wt%) Zn alloy upon the pre-precipitation or clustering phenomenon.
The results are as follows:
(1) The rate of clustering of Zn atoms is reduced by the addition of Cr, Mn and Zr, but general features of pre-precipitation in these ternary alloys are not different from those in Al-2.5 at%Zn binary alloy since these third elements in the above-mentioned range do not interact with Zn atoms.
(2) The decrement in the rate of clustering of Zn atoms increases in the order of Mn<Cr<Zr, particularly by the addition of Mn 0.2∼0.3 at%, Cr 0.1∼0.2 at% and Zr 0.03∼0.2 at% which is characterized by the existence of the second phases.
(3) This effect can be more reasonably explained in terms of the increase in boundary area by grain refining and in dislocation density by remaining of dislocations introduced by plastic deformation which could act as sinks to cause the decrease in the concentration of quenched-in vacancies, rather than the binding energy between an atom of the third elements and a vacancy which is greater than that between a Zn atom and a vacancy.