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Research Papers

Stress Corrosion Cracking Behavior of Tungsten Inert Gas Welded Age-Hardenable AA6061 Alloy

[+] Author and Article Information
Simge Gencalp Irizalp

Department of Mechanical Engineering,
Manisa Celal Bayar University,
Muradiye, Manisa, 45140 Turkey
e-mail: simge.gencalp@cbu.edu.tr

Burcak Kardelen Koroglu

Department of Mechanical Engineering,
Manisa Celal Bayar University,
Muradiye, Manisa, 45140 Turkey
e-mail: burcakkoroglu@gmail.com

Contributed by the Materials Division of ASME for publication in the Journal of Engineering Materials and Technology. Manuscript received July 6, 2018; final manuscript received December 18, 2018; published online March 20, 2019. Assoc. Editor: Antonios Kontsos.

J. Eng. Mater. Technol 141(4), 041003 (Mar 20, 2019) (12 pages) Paper No: MATS-18-1198; doi: 10.1115/1.4042662 History: Received July 06, 2018; Accepted December 31, 2018

The effects of two temper conditions (T4 and T6 heat treatments) upon the stress corrosion cracking (SCC) of AA6061 plates have been investigated in this work. AA6061 alloys were double-side-welded by the tungsten inert gas (TIG) welding method. SCC behavior of both the as-welded and as-received alloys was reported. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine the precipitate structure of the thermal-altered zones and the base metal (BM), and also the hardness variations were examined using microhardness testing (Vickers hardness). The small-size precipitate structures in the T6 tempered alloy and the coarser precipitate structures in the T4 tempered alloy were found by microstructural investigations. As a result, T4 temper heat treatment of this alloy considerably reduced its susceptibility to stress corrosion cracks due to relatively coarse and more separate precipitate morphology. In welded specimens, SCC failure occurred in the area between the heat-affected zone (HAZ) and the base metal. Stress corrosion resistance in the fusion zone was strong in both temper conditions. The aim of this work was to obtain the effects of heat treatment and welding on SCC behavior of the age-hardenable aluminum alloy. The authors conclude that a deep insight into the SCC resistance of AA6061 alloy indicates the precipitate particle distributions and they are the key point for AA6061 alloy joints in chloride solution.

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Figures

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Fig. 1

SCC-SSRT specimen dimensions

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Fig. 2

Macrographs of the TIG weld joint (a) and the heat-affected zone after etching (b)

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Fig. 3

State diagram of the phases obtained from AA6061: (a) up to 100% and (b) up to 1.5% in weight

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Fig. 4

State diagram of the phases obtained from AlMg5: (a) up to 100% and (b) up to 4% in weight

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Fig. 5

Optical micrographs at two magnifications of the fusion zone: (a) AA 6061-T4 alloy and (b) AA 6061-T6 alloy

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Fig. 6

Optical micrographs at two magnifications of the heat-affected zone: (a) AA 6061-T4 alloy and (b) AA 6061-T6 alloy

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Fig. 7

Optical micrographs of the partially melted zone: (a) AA 6061-T4 alloy and (b) AA 6061-T6 alloy

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Fig. 8

Optical micrographs of the base metal: (a) T4 tempered alloy and (b) T6 tempered alloy

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Fig. 9

SEM micrograph of the base metal: (a) T4 tempered alloy and (b) T6 tempered alloy

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Fig. 10

EDX analysis showing the elements containing the Mg-rich phase (a) and the Fe-rich phase (b)

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Fig. 11

SEM micrograph of the fusion zone AA6061-T4

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Fig. 12

EDX analysis showing the elements containing the Cu-rich phase (a) and the Si particle (b)

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Fig. 13

Microstructure of the AA6061 in the as-welded condition: FZ (a) T4 and (b) T6; BM (c) T4 and (d) T6

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Fig. 14

Microstructure of the HAZ in the as-welded AA6061: close to the FZ (a) T4 and (b) T6; closer to the BM (c) T4 and (d) T6

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Fig. 15

Microhardness profiles of the TIG-welded AA6061

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Fig. 16

Macrographs of the TIG-welded AA6061-T6 sample failed during the SSRT test in (a) air and (b) corrosive environment; show failured region between the HAZ and the BM

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