Study on Removal Mechanism of Oxides and Surface Quality Regulation During Integrated Pulsed-Continuous Laser Cleaning of Q235B Carbon Steel Plates

Abstract

In this paper, we used a pulsed laser for cleaning experiments on Q235B carbon steel to investigate the effects of different process parameters on the surface cleaning quality. On this basis, a new cleaning method was innovatively proposed to improve oxide removal efficiency, microstructure and mechanical property of cleaned samples. This investigation was carefully conducted using a confocal laser scanning microscope, scanning electron microscope, electron back-scattered diffraction energy diffraction spectrum and other methodologies. The results showed that pulsed laser cleaning of Q235B carbon steel was the most effective at laser linewidth of 50 mm, pulsed frequency of 500 kHz and cleaning speed of 15 mm/s. A great deal of craters were formed on the surface of cleaned samples due to the thermal shock of pulsed laser. Compared with other laser cleaning methods, integrated pulsed-continuous laser cleaning had an obvious effect in raising the oxide removal efficiency and reducing the surface roughness. The ridge structures on the sample surface can be also successfully eliminated, subsequently achieving smooth structures. Fine-crystalline structures were formed near the surface of tested samples, which significantly decreased the crystal orientation and increased the number of small angle grain boundary and the GND density. The average hardness of integrated pulsed-continuous laser cleaning samples was much higher than that of pulsed laser cleaning samples. The improvement of hardness was mainly on account of grain refinement in the samples, which effectively improved the mechanical property of the material itself. In addition, a physical model was proposed to illustrate the oxide removal mechanism of integrated pulsed-continuous laser cleaning samples. This research offered new theoretical and technical support for solving the long-standing problem of the efficiency and quality in laser cleaning, which significantly broadened the application of laser technology in manufacturing fields.

Keywords: Integrated pulsed-continuous laser cleaning, Q235B carbon steel, Surface quality, Microstructure, Removal mechanism of oxides