|
Experiments are performed to investigate the laser irradiation effects on thin aluminum alloy sheets subjected to tangential airflow. The wind blower generated airflow with a speed of about 100 m/s along the surface. For comparison, experiments in the absence of airflow are also conducted. Moreover, in order to know whether the combustion reaction takes place during the irradiation, we vary the composition of flow from air to nitrogen. The displacements of the sheets center are measured to see whether the tangential flow has a mechanical effect. The maximum temperature of the sheet is lower than 550 ℃ after 2 seconds irradiation with the laser power density of 173W/cm2. Accordingly, the structural parameters of aluminum alloy do not have distinct change and so do the features of sheets. The temperature curves in the air flow and nitrogen flow keep the same and both lower than that in no flow case. Moreover, the displacements measured in three cases do not have obvious difference. These experiment results indicate that the combustion reaction can hardly happen and the tangential flow only has a cooling effect. The maximum temperature reaches 600 ℃ when the laser power density rises to 400 W/cm2. Such a high temperature makes that the elastic modulus of aluminum alloy drops rapidly, which greatly softens the alloy sheets. The plastic distort of irradiated sheets confirmed this process. When the power density rises to 450W/cm2 big melt-through phenomenon is observed and there is viscous dripping under gravity in the no-flow case. However, in air flow and nitrogen flow, we can see the removal of macroscopic unmelted pieces of aluminum alloy sheet. The results indicate that the tangential flow mainly has two effects including cooling the target and removing the unmelted metal when the material is fully softened.
|
