Effect of local heating by ultrashort pulsed laser on Fe–Si–B–Cr amorphous alloys and its influence on blanking machinability

Abstract

We propose a novel blanking method to improve the machinability of amorphous alloys by taking advantage of changes in mechanical properties during local heating. The local heating is achieved through an ultrashort pulsed laser with a low thermal effect, allowing us to control the size and structure of heat-affected zones by adjusting laser power, pulse width, and shot numbers. This method hence causes phase transformation only in the blanking area. Namely, heat storage effects increased with a prolonged ablation process, and crystallization was observed at a repetition rate of 200 kHz or more. A fully crystallized microstructure, which formed at elevated temperatures, was seen at the center of the laser irradiation, while, as the distance from the irradiation point increased, small crystallites are found to disperse in the amorphous matrix. In addition, a thin crystalline phase appeared on the surface layer of the crystallized region. In general, the locally heated area was embrittled by the aforementioned structural changes, and consequently, the blanking resistance decreased with an increase in the crystallized area. Yet, it was found that laser irradiation which did not bring about crystallization also led to a decrease in the blanking resistance, showing that thermal effects below the crystallization temperature are still effective in reducing the blanking resistance. Additionally, the blanked cross-section of the locally heated specimen showed good surface quality without defects such as a large shear droop, which often occurs when punching amorphous alloys.