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Research Papers: JOINING

Influence of Weld Defects and Postweld Heat Treatment of Gas Tungsten Arc-Welded AA-6061-T651 Aluminum Alloy

[+] Author and Article Information
Mohammad W. Dewan

Department of Mechanical
and Industrial Engineering,
Louisiana State University and A&M College,
2508 Patrick F. Taylor Hall,
Baton Rouge, LA 70803
e-mail: mdewan1@tigers.lsu.edu

M. A. Wahab

Professor
Department of Mechanical
and Industrial Engineering,
Louisiana State University and A&M College,
2508 Patrick F. Taylor Hall,
Baton Rouge, LA 70803
e-mail: wahab@me.lsu.edu

Ayman M. Okeil

Associate Professor
Department of Civil
and Environmental Engineering,
Louisiana State University and A&M College, 3513E Patrick F. Taylor Hall,
Baton Rouge, LA 70803
e-mail: aokeil@.lsu.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received December 10, 2014; final manuscript received March 26, 2015; published online September 4, 2015. Assoc. Editor: Jingjing Li.

J. Manuf. Sci. Eng 137(5), 051027 (Sep 04, 2015) (9 pages) Paper No: MANU-14-1665; doi: 10.1115/1.4030333 History: Received December 10, 2014

Welding defects and the reduction of mechanical performances are the foremost problems for fusion welded aluminum alloys joints. The influences of weld defects and postweld heat treatment (PWHT) on tensile properties of gas tungsten arc (GTA) welded aluminum alloy AA-6061-T651 joints are investigated in this current study. All welded specimens are nondestructively inspected with phased array ultrasonic testing (PAUT) to classify weld defect and measure the projected defects area-ratio (AR). Ultimate tensile strength (UTS) decreased linearly with the increase of the size of weld defect but tensile toughness behaved nonlinearly with defect size. Depending on defect size, defective samples' joint efficiency (JE) varied from 35% to 48% of base metal's (BM) UTS. Defect-free as-welded (AW) specimens observed to have 53% and 34% JE based on UTS and yield strength (YS) of BM, respectively. PWHT was applied on defect-free welded specimens to improve tensile properties by precipitation hardening, microstructures refining, and removal of postweld residual stresses. Solution treatment (ST) (at 540 °C) followed by varying levels of artificial age-hardening (AH) time was investigated to obtain optimum tensile properties. For GTA-welded AA-6061-T651, peak aging time was 5 hr at 180 °C. PWHT specimens showed 85% JE based on UTS and up to a 71% JE based on YS of BM. However, toughness values decreased about 29% due to the presence of precipitate-free fusion zones. The experimental investigations can be used to establish weld acceptance/rejection criteria and for the design of welded aluminum alloy structures.

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Figures

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Fig. 1

Welding configurations and tensile specimens (all dimensions are in millimeter)

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Fig. 2

The C and S-scan views of tensile test samples obtained with PAUT: (a) no-defect, (b) voids, (c) LOF, and (d) LOP

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Fig. 3

Cross-sectional view of tensile tested specimens with different weld defects obtained with OM: (a) no defect, (b) voids, (c) LOF, and (d) LOP

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Fig. 4

Plot shows the relationship between the defect sizes measured with OM and PAUT

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Fig. 5

Tensile test curves of GTA-welded AA-6061-T651 aluminum alloy with different welding defect

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Fig. 6

Tensile strength versus defect cross-sectional AR measured with PAUT and OM

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Fig. 7

Toughness versus area reduction ratio measured with PAUT and OM

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Fig. 8

SEM fractographs of: (a) BM of unwelded specimen, (b) weld metal of AW specimen, and (c) HAZ metal of AW specimen

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Fig. 9

SEM fractographs of tensile tested welded specimens with different types of weld defects: (a) LOP, (b) LOF, and (c) void

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Fig. 10

Variations of tensile strength and toughness due to PWHT

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Fig. 11

Effect of PWHT on hardness profile

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Fig. 12

Effect of PWHT on fusion zone microstructure. Finer microstructures are observed in (b) heat-treated (STAH-5h) specimen as compared to (a) AW specimen.

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Fig. 13

SEM fractographs of PWHT samples: (a) only AH, (b) STAH-5h, and (c) STAH-18h

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