Microstructure and Mechanical Properties of a Laser Treated Al Alloy

An Al-Cu-Mg alloy, Al 2024-T3, was exposed to laser treatments at various scan velocities. In this paper the microstructural features and mechanical properties are reported. As far as the mechanical property is concerned a striking observation is a minimum in the hardness value at a laser scan velocity of 1/2 cm/s. Usually an increasing hardness with increasing laser scan velocities is reported in the literature. This remarkable property could be explained based on the microstructural features observed by transmission electron microscopy. It turned out that depending on the laser scan velocity nucleation and growth of precipitates could either be enhanced or suppressed. In addition at low scan velocities helical dislocations are observed which may contribute to an increase of the hardness. After subsequent shot peening, in all cases the formation of precipitates was observed, independent of the laser scan velocities originally applied. This phenomenon of precipitation, induced by shot peening afterwards is most striking at a high concentration of alloying elements in solid solution.