Dispersion characteristic of surface acoustic waves propagating through aluminum alloy heated by millisecond laser

Surface acoustic waves(SAWs) exist dispersion when they propagate along material with elastic properties distributing heterogeneously over depth among near-surface area, and the dispersion spectrum can be applied to reconstruct elastic properties' distribution. A millisecond laser was assembled to heat aluminum alloy, resulting in a temperature gradient over depth in sample. As temperature dependence elastic properties distributing heterogeneously over depth because of the temperature gradient, SAWs will disperse when propagate across laser irradiated area, and materials' temperature dependence elastic properties can be obtained by analyzing the dispersion curve. Dispersion characteristic of laser-generated surface acoustic waves propagating along aluminum alloy with a temperature gradient near subsurface induced by millisecond laser irradiation was studied experimentally. The dispersion effects induced by surface roughness was removed by measuring the dispersion of SAWs propagating along the sample with millisecond irradiation and without it. The experimental data showed that heterogeneous distribution of elastic properties induced by the temperature can lead SAWs dispersing normally. Theoretical model based on effective velocity method was established to calculate the dispersion curve. Theoretical results agreed well with the experiment data. It was shown from experimental and theoretical results that temperature gradient formed by millisecond laser irradiation in aluminum alloy with surface temperature being 154°C can induce about 65m/s SAWs velocity shift at 35MHz.Experimental and theoretical results demonstrate the feasibility of this SAWs dispersion technique cooperated with millisecond laser to study materials' temperature dependence mechanical properties. Results of this paper may provide theoretical and experimental basis for inversing materials' temperature dependence elastic properties.