Pore closure effect of laser shock peening of additively manufactured AlSi10Mg

Abstract

This article reports on an exceptional insight provided by nondestructive X-ray tomography of the same samples before and after laser shock peening (LSP). The porosity in two additively manufactured aluminum alloy (AlSi10Mg) tensile samples before and after LSP was imaged using identical X-ray tomography settings and overlap of the data was performed for direct comparison. The results indicate clearly that near-surface pores are closed by the process, while internal pores remain unaffected. LSP has become well known as a method to improve the fatigue properties of materials, including those of additively manufactured aluminum alloys. This improvement is usually attributed to the compressive residual stress induced by the process. The additional effect of closure of near-surface pores that is illustrated in this work is of interest for additive manufacturing because additive manufacturing is not yet able to produce completely pore-free components. Since the critical pore initiating fatigue cracks are always attributed to surface or subsurface pores, the closure of these pores may play an additional role in improving the fatigue properties. While more work remains to unravel the relative importance of near-surface porosity compared to the compressive residual stress effect, this work clearly shows the effect of LSP—closing of pores near the surface. For the processing conditions demonstrated here, all pores up to 0.7 mm from the surface are closed without damaging the surface, while higher peening power results in surface damage.