Laser Shock Peening on a 6056-T4 Aluminium Alloy for Airframe Applications

Abstract:

Laser Shock Peening (LSP) is a material enhancement process used to introduce compressive residual stresses in metallic components. This investigation explored the effects of different combinations of LSP parameters, such as irradiance (GW/cm²) and laser pulse density (spots/mm²), on 3.2 mm thick AA6056-T4 samples, for integral airframe applications. The most significant effects that are introduced by LSP without a protective coating include residual stress and surface roughness, since each laser pulse vaporizes the surface layer of the target. Each of these effects was quantified, whereby residual stress analysis was performed using X-ray diffraction with synchrotron radiation. A series of fully reversed bending fatigue tests was conducted, in order to evaluate fatigue performance enhancements with the aim of identifying LSP parameter influence. Improvement in fatigue life was demonstrated, and failure of samples at the boundary of the LSP treatment was attributed to a balancing tensile residual stress.

References

[1] R. Fabbro et al., Physics and applications of laser-shock processing, J. Laser Appl. 10 (1998) 265-279.

[2] K. Ding, L. Ye, Laser shock peening performance and simulation, Woodhead Publishing Limited, Cambridge, England, (2006).

[3] A.H. Clauer, Laser shock peening for fatigue resistance, Surface Performance of Titanium (1996) 217-230.

[4] Y. Sano et al., Improvement in fatigue performance of friction stir welded AA6061-T6 aluminium alloy by laser peening without coating, Materials and Design 36 (2012) 809-814.

DOI: 10.1016/j.matdes.2011.10.053

[5] M. Boustie et al., Laser shock waves: fundamentals and applications, Conference proceeding in 1st International Symposium on Laser Ultrasonics: Science, Technology and Applications, Montreal, Canada (2008).

[6] C.B. Dane et al., U.S. Patent 7, 960, 671 B2 (2011).

[7] P.J. Withers, Residual stress and its role in failure, Rep. Prog. Phys. 70 (2007) 2211-2264.

DOI: 10.1088/0034-4885/70/12/r04

[8] J.L. Ocaña et al., Laser shock processing as a method for surface properties modification of metallic materials, In: Proceedings of the 9th International Conference on Shot Peening: Paris, France, (2005) 446-471.

[9] SensoSCAN neox v. 3. 2. 3, Sensofar-Tech, S.L., Terrassa, Spain.

[10] H. Song, Experimental and numerical analysis of the distribution of residual stresses induced by laser shock in aluminium alloys, PhD diss., ParisTech (2010) (in French).

[11] M. Obata et al., Effect of laser peening on residual stress and stress corrosion cracking on stainless steel, In: Proceedings of the 7th International Conference on Shot Peening: Warsaw, Poland, (1999) 387-394.

DOI: 10.1002/3527606580.ch33

[12] M. Dorman et al., Effect of laser shock peening on residual stress and fatigue life of clad 2024 aluminium sheet containing scribe defects, Materials Science and Engineering 548 (2012) 142-151.

DOI: 10.1016/j.msea.2012.04.002

[13] C.S. Montross et al., Laser shock processing and its effects on microstructure and properties of metal alloys: a review, International Journal of Fatigue 24 (2002) 1021-1036.

DOI: 10.1016/s0142-1123(02)00022-1

[14] P. Peyre et al., Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour, Material Science and Engineering 210 (1996) 102-113.

DOI: 10.1016/0921-5093(95)10084-9

[15] J.L. Ocaña et al., Experimental assessment of the influence of irradiation parameters on surface deformation and residual stresses in laser shock processed metallic alloys, Applied Surface Science 238 (2004) 501-505.

DOI: 10.1016/j.apsusc.2004.05.246