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. 23    No. 5    May 2013

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“Abnormal transient creep” in fine-grained Al-5356 alloy observed at low strain rates by high-resolution strain measurement
Jun-jie SHEN1, Kenichi IKEDA2, Satoshi HATA2, Hideharu NAKASHIMA2

1. School of Mechanical Engineering, Tianjin University of Technology, Tianjin 300191, China;2. Department of Electrical and Materials Science, Faculty of Engineering Sciences,Kyushu University, Kasuga, Fukuoka 816-8580, Japan

Abstract:Transient creep at very low strain rates (less than 10-10 s-1) is still unclear. The traditional uniaxial creep testing is less useful due to unsatisfied resolution strain (~10-6). To study transient creep behavior at such low strain rates, a high-resolution strain measurement using the helicoid spring specimen technique was employed in a fine-grained Al-5356 alloy at temperatures ranging from 0.47Tm to 0.74Tm (Tm: melting point). To clarify transient creep mechanism at such low strain rates, transmission electron microscopy (TEM) was used in microstructure observation of crept specimens. The abnormal transient creep, high temperature strengthening at T>Tp (Tp: the phase transformation temperature, 0.58Tm) or intermediate temperature softening at 0.4Tm<T£Tp and double-normal type (creep curves including double work-hardening stages) at T=Tp, were firstly observed. The substructure observation in a crept specimen at T=0.58Tm and e=1×10-4 shows pile-up dislocations including many small jogs with equal interval, and dislocations emitted from grain boundaries. The b-Al3Mg2 phase dissolves under the condition of testing temperatures higher than 523 K, which causes solid-solution quantity of Mg atoms to increase. Therefore, the “abnormal transient creep” may be related to the difference of solid solution strengthening caused by phase change during the creep tests.

 

Key words: Al-5356 alloy; transient creep; phase change; low strain rate

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

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

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