Structural life enhancement on friction stir welded AA6061 with optimized process and HFMI/PIT parameters
This novel study presents an unconventional approach to find the best governing process parameters of high frequency mechanical impact technique based on multi-objective optimization method. In this investigation, the post-weld mechanical treatment is aimed to enhance fatigue resistance of structural friction-stirred weld subjected to fluctuating loads by obtaining nominal sub-surface hardness. The experimental study was conducted on aluminium alloy AA 6061 with thickness of 6 mm under varied parameters centred on indenter diameter, air pressure and impact frequency. The investigation began with obtaining optimum parameters for single response by using conventional Taguchi method with L9 orthogonal array. Next, advanced optimization approach by means of multi-objective Taguchi method attempts to consider the multiple responses simultaneously which are sub-surface hardness and structural life. As the final results, the optimum value was acquired by calculating the total normalized quality loss and multiple signal-to-noise ratios based on unequal desirability. The significant level of the parameters was evaluated by using analysis of variance. Furthermore, the second-order model for predicting the objectives was derived by applying response surface methodology. It can be summarized that, first, the affecting parameters to obtain superior structural life can be ordered at significant level of ca. 65, 25 and 10% for air pressure, impact frequency and indenter diameter, respectively. Secondly, using subsequent post-weld mechanical treatment, the life cycle number can be extended up to 12 times on friction-stirred weld. Finally, based on the experimental confirmation test, the proposed method can effectively estimate the structural life and surface hardness within the acceptable range of relative error.
KeywordsFatigue life Friction stir welding (FSW) High frequency mechanical impact (HFMI) Pneumatic impact treatment (PIT) Optimization
Unable to display preview. Download preview PDF.
- 1.Almanar IP, Hussein Z (2011) Basic consideration for weldment formation in friction stir welding. Nova Science Publishers, New York, pp 45–53Google Scholar
- 7.Gerster P, Schäfers F, Leitner M (2013) Pneumatic Impact Treatment (PIT)—Application and Quality Assurance, IIW Document XIII-WG2–138-13 pp 1–11Google Scholar
- 9.Leitner M, Stoschka M, Eichlseder W (2012) Contribution to the fatigue enhancement of thin-walled, high-strength steel joints by high frequency mechanical impact treatment. IIW Document XIII-2416-12Google Scholar
- 10.Nitschke-Pagel T, Eslami H, Dilger K (2013) Influence the deformation intensity on the fatigue strength of aluminium welds with different mechanical surface treatments, IIW-Doc. XIII-2483-13Google Scholar
- 16.A. S. Ribeiro, A. M. P. De Jesus, and I. Feup (2009) Fatigue behaviour of welded joints made of 6061-T651 aluminium alloy. Aluminium Alloy, Theor Appl ISBN 978–953–307-244-9Google Scholar
- 18.ISO/TR 14345:2012 (EN) Fatigue — Fatigue testing of welded components — GuidanceGoogle Scholar
- 21.ISO EN 5817:2014 Welding—Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded)—Quality levels for imperfectionsGoogle Scholar
- 22.ISO 6507-2:2005 Metallic materials—Vickers hardness test—Part 2: Verification and calibration of testing machinesGoogle Scholar