Rapid solidification of aluminum die cast alloys by high-power laser radiation

摘要

Abstract: Rapid solidification of aluminum alloys during the remelting process using high power laser radiation results in refined effects of the solidified grain texture and improved wear resistance and material hardness. High temperature gradients can be achieved, and energy coupling into the aluminum alloy is locally restricted and can be precisely controlled. For the adjustment of defined grain textures, the dynamic behavior of the melted material on the irradiated material surface is of high interest. Current activities at the Laser Zentrum Hannover eV are focused on a new visualization system for locally and temporally highly-resolved visualization of the aluminum alloy surface during short pulse laser interaction. Experimental measurements have been performed to determine the heating and cooling velocities. The main aim of the work is the correlation of image information and the resulting grain structures dependent on material properties and actual laser beam and processing parameters. The aluminum samples are remelted using an Nd:YAG solid-state slab laser system providing short pulse durations and high pulse power. Frequency selective irradiation of the melting zone is realized by using a frequency-doubled Q-switched Nd:YAG laser system. Image information from the processing zone is obtained using a CCD-camera, coaxially mounted to the processing zone. By using pulse durations in the ns-range and high beam intensities of the illuminating laser source, time resolutions for process visualization can be realized, with orders of magnitudes higher than existing visualization techniques. Image data related to the temporal development of the solid and liquid isotherms are compared to the results of numerical calculations using the finite difference method.!7