Diffusion processes for aluminum-silicon coatings on low carbon sheet steels during austenizing have been investigated. Temperature profiles were imposed with closed-loop control of a motorized linear slide that moves samples through a tube furnace. Heat treatment variables were heating rate, hold temperature, and hold time. Subsequent analysis included scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and surface roughness measurements. The evolution of the coating was tracked by following the formation of seven main microstructural regions. In order to observe the cross-sectional microstructure without any mechanical influence of the preparation process, a focused-ion beam (FIB) was used. The effects of the various heat treatment parameters were evaluated. The resulting observations and data enhance the understanding of the diffusion process and provide information needed to optimize the heat treatment.
The increased desire to use advanced, high-strength steels for lightweight automotive structural components requires better understanding of thermo-mechanical behavior and appropriate experimental data for developing constitutive models. Thermo-mechanical studies are particularly important for understanding and optimizing hot-stamping processes which produce both complex and high-strength components. The experimental setup presented herein is capable of characterizing the thermo-mechanical behavior of such steels with strain rates up to approximately 1 s -1 and temperatures as high as 850°C. The main parts of the apparatus are a high-speed camera, a load frame, and a box furnace. For the determination of strain, a simple image-processing program was developed. The strain was determined in three sections that span the entire gauge length of the specimen. Thus, the onset of localization could be more accurately determined. Stress versus strain data for various strain rates and temperatures are presented.
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