Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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中国有色金属学报(英文版)

Transactions of Nonferrous Metals Society of China

Vol. 16    No. 5    October 2006

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Retrogression and re-aging treatment of Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr aluminum alloy
FENG Chun(冯 春)1, LIU Zhi-yi(刘志义)1
NING Ai-lin(宁爱林)1,2, LIU Yan-bin(刘延斌)1, ZENG Su-min(曾苏民)1

1. School of Materials Science and Engineering, Central South University, 
Changsha 410083, China; 
2. Department of Laser Technology and Materials, Shaoyang Institute,
 Shaoyang 410020, China

Abstract: The effect of retrogression and re-aging(RRA) heat treatment on the microstructure and mechanical properties of a low frequency electromagnetic casting alloy as Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr was investigated by tensile properties test, Vickers hardness, electrical conductivity test, DSC analysis, SEM and TEM observation. The results show that RRA heat treatment can improve the stress corrosion cracking(SCC) properties with retention of the high strength of T6 level. After preaging at 100 ℃ for 24 h, retrogression at 200 ℃ for 7 min, and then re-aging at 100 ℃ for 24 h, the alloy obtains tensile strength up to 795 MPa, yield strength up to 767 MPa, maintains 9.1% elongation, and electric conductivity of 35.6%IACS. TEM observation shows that the re-dissolution of GP zone and η′ phase in the early stage of regression leads to the decrease of hardness, then the increase in the volume fraction of η′ and η phases leads to the increase again in the peak value, and finally the general coarsening of all particles results in a softening of the alloy. Meanwhile it is found that the conventional T6 heat treatment as the preaging and re-aging regime is not the optimum regime to the RRA treatment of the high-zinc content super-high strength aluminum alloy.

 

Key words: Al-Zn-Mg-Cu alloy; retrogression; re-aging; microstructure; mechanical properties; stress corrosion cracking

ISSN 1004-0609
CN 43-1238/TG
CODEN: ZYJXFK

ISSN 1003-6326
CN 43-1239/TG
CODEN: TNMCEW

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