Liquid metal embrittlement is the reduction in the elongation to failure that can be produced when normally ductile solid metals are stressed while in contact with a liquid metal such as gallium. We have studied extraordinary-fast penetration process of gallium in aluminum alloys by measuring Rayleigh-wave velocity and attenuation using laser-induced ultrasound. The results of attenuation measurements showed two-stage penetration processes: the fast one is forming a structure like a spider's web along the surface with the speed of 28 μm/s, and the slower one is the homogeneous penetration into the bulk. The velocity showed the decrease with time evolution, reflecting the slower stage.
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