Study of fatigue crack growth of al 6061-T6 welds obtained by gas metal arc welding along longitudinal direction

Abstract

The behavior of fatigue crack growth(FCG) plays a vital role in the design and performance of modern structural materials like Al 6061-T6 alloy. Al 6061-T6 is an alloy of Al-Mg-Si which is artificially aged under T6 condition. In the present study, Al 6061-T6 plates of 6 mm thickness welded by a gas metal arc welding(GMAW) technique using an ER-5356 as filler wire. The microhardness profile was obtained through Vickers microhardness test. The pre-qualification tests such as X-ray radiography, tensile, and bending tests were carried out on base metal (BM), heat-affected zone (HAZ), and weld zone (WZ)along rolling direction to study the mechanical behavior. The fatigue crack growth rate (FCGR) tests on the three zones were carried out as per ASTM E-647 standards under stress ratios of 0.1, 0.3, and 0.5. The WZ possessed highest FCGR compared to BM and HAZ. The lowest fracture toughness (K_c) was found for WZ, which is due to fusion of filler wire with BM. The microstructural transformation in HAZ from very fine needle shape β'' precipitates to coarse bar shape β' precipitates produced by the thermal effect during the welding process resulting in moderate FCGR compared to WZ and BM. Mechanical strength and microstructure regeneration during the welding thermal cycle are the two important factors that affect the FCGR in all zones. Fractographic analysis was carried out using a scanning electron microscope (SEM) to study the crack initiation, final fracture, nature of the fracture, and causes of failure under various stress ratios.

Keywords:

• Al 6061-T6
• GMAW
• fatigue crack growth rate
• SEM

REVIEWING EDITOR:

• Pham D. T., University of Birmingham, UK

SUBJECTS:

• Structural Mechanical Engineering
• Fracture & Damage Mechanics
• Mechanical Engineering
• Mechanical Engineering Design

Disclosure statement

All authors have seen and agree with the contents of the manuscript and there is no financial interest to report. We certify that the submission is original work and is not under review at any other publication.

Author contribution statement

All authors take public responsibility for the content of the work submitted for review. The contributions of all authors have been described in the following manner:

The authors confirm contribution to the paper as follows: Study conception and design: Dr. P C Arunakumara, Sagar H N, Bimal Gautam. Data collection: Sagar H N. Analysis and interpretation of results: Dr. P C Arunakumara, Sagar H N, Dr. S Rajeesh. Draft manuscript preparation: Dr. P C Arunakumara, Sagar H N. All authors reviewed the results and approved the final version of the manuscript.

Data availability statement

The author confirmed that the data supporting the findings of this study are within the article. Raw data supporting the findings of this study are available from the corresponding author upon reasonable request.

Novelty and application

The literature review revealed a lack of research on the fatigue crack growth in Al 6061-T6 welds obtained by gas metal arc welding methods in three regions such as the base metal, the heat-affected zone, and the weldment.

The present study investigates the characteristics of fatigue crack growth under stress ratios of R = 0.1, 0.3, and 0.5 in base metal, weldment, and the heat-affected zone. The results suggest that while the stress ratio increases, there is a substantial variation in the growth of fatigue crack. The objective of the present work is to study the FCG in the 3 zones of the welded plate along the longitudinal direction, the change in microstructure during the welding thermal cycle, and the effect of the stress ratio on the fatigue crack growth rate.

Acknowledgments

The authors acknowledge the DRDO, ARMREB, and India for their financial support. The authors express their gratitude to Dr. Bhupender Singh Rawal and Mr. Bimal Gautam for their constructive advice. The authors also thank the principal and head of the mechanical engineering department at RIT, Bangalore, for their unwavering support.

Additional information

Funding

The authors greatly acknowledge the financial support of the Defence Research and Development Organization (DRDO), India.

Notes on contributors

Arunakumara P. C.

Dr. P. C. Arunakumara, PhD (Fracture Mechanics), MS Ramaiah Institute of Technology, Research Interest: Fatigue and Fracture, Mechanical Vibrations.

Sagar H. N.

H. N. Sagar, MTech (Machine Design), MS Ramaiah Institute of Technology Research Interest: Fatigue and Fracture.

Bimal Gautam

Bimal Gautam (Mechanical Engineering) MTech, R & D Engineers, Pune, Research Interest: Material Characterization.

Rajeesh S.

Dr. S. Rajeesh, MTech (Mechanical Engineering), MS Ramaiah Institute of Technology Research Interest: CFD, Fatigue and Fracture.