Acoustic Emission Analysis of Aluminum Specimen Subjected to Laser Annealing

Abstract

This paper deals with the study of acoustic emissions (AE) from aluminum Al5068 specimen during local annealing process by a laser diode source. The heating cycle, obtained by irradiating the surface of the specimen, causes a change in the local stress state which can be studied by X-Ray diffractometry; at the same time acoustic emissions can be recorded as a consequence of residual stress relieving.

This hybrid approach provides evidence of the presence of a correlation between stress relieving and the number of signals of acoustic emissions recorded during the heating and the cooling stages. Annealing cycle was repeated several times and acoustic emissions were detected during each cycle; the amount of residual stresses along the longitudinal direction was measured at the end of each cycle as well. The number of acoustic signals exhibits the typical behavior due to the Kaiser effect while residual stresses show a quite regular decrease from cycle to cycle. Mechanical tensile tests have also been performed on the same specimen tested at four different loads. In this case too, experimental results show evidence of Kaiser effect, however a steeper reduction of the number of signals is observed with respect to the thermal tests.