Uticaj termičkog tretmana retrogresije i ponovnog starenja na mehaničke karakteristike legure EN AW 7049A-T6

Jelena Marinković,Ljubica Radović

doi:10.5937/str2101008m

Abstract

Aluminum alloys of 7xxx series have the highest strength among all aluminium alloys, but they are prone to the corrosion-induced damage. The retrogression and re-aging heat treatment (RRA) is a heat treatment process applied on the 7xxx series aluminum alloy in T6 temper condition to provide a significant improvement of the corrosion resistance with or without small loss in its strength. The paper presents the influence of RRA treatment on the electrical conductivity and mechanical properties of the aluminum EN AW 7049A-T6 alloy. The retrogression heat treatment was performed at various temperatures (from 180 C to 280 C) and times (from 3 min to 45 min), while re-aging was performed at 120 °C for 24 hours. It has been found that with increasing both temperature and time of retrogression, hardness and strength decrease but the toughness of the alloy increases in comparison to the initial T6 temper. Contrary to hardness values, electrical conductivity rises with an increase in holding time and temperature of retrogression.

Highlights

ALUMINUM alloys of the 7xxx series belong to the group of alloys in which high strength, toughness and corrosion resistance are achieved by applying heat treatment regimes
This research studied the effect of retrogression and reaging heat treatment (RRA) on the electrical conductivity and mechanical properties of the aluminum EN AW 7049A alloy
Initial increase in electrical conductivity was due to dissolution of GP-zones matrix enriched in the strengthening elements, Zn and Mg, which leads to supersaturated solid solution and nucleation and growth of the

Summary

Introduction

ALUMINUM alloys of the 7xxx series belong to the group of alloys in which high strength, toughness and corrosion resistance are achieved by applying heat treatment regimes. The precipitation process in 7xxx series alloys generally takes place according to the following scheme 1, 2 : SSS (supersaturated solid solution) stable coherent GP zones semi-coherent intermediate ' (MgZn2) phase stable incoherent (MgZn2) or T (AlZnMgCu) phase. During the 70's, in our country extensive researches were conducted on the 7xxx series aluminum alloys. These researches had а goal of developing new aluminum alloys that would meet the requirements of high strength, toughness, good plasticity and corrosion resistance 6, 7. Together with the “Impol Aluminum industry” from Slovenia, the alloy based on the well-known aluminum alloy EN AW 7049A was developed, according to the EU standard, SRPS EN 573-3

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