The subject of research is car exhaust system piping made of chromium–nickel steel of grade AISI304L with a unique, complex shape that was obtained by hydroforming technology. The purpose of the research was to determine the relation between the microstructure features, surface condition, hardness and the stresses on the external surface as determined by the sin2ψ X-ray method. We found that the stresses were tensile and correlated with the steel hardness, i.e. they were greater where the hardness was higher. Moreover, longitudinal stresses showed a relationship with pipe wall thickness, while circumferential stresses did so only partially. According to our data, the greatest value of stress determined in the pipe amounted to 290 MPa, and was close to the yield point of the strain hardened 304L steel. As depicted via XRD and SEM examination, the pipe stress level and hardness were influenced by the transition γ→α’. Furthermore, in the region of higher stress and hardness, the amount of martensite was 10 vol.%. We also noted that the pipe’s outer surface when subjected to friction against the die shows lesser roughness compared to its inner surface upon exposure to water under pressure.

The continuous increase in demand for aluminum coatings for the automotive industry is associated with the need to improve their quality in terms of protective and mechanical properties. The aluminum coatings produced hot-dip, on the border with the steel substrate formed intermediate phases FeAl3, and Fe2Al5, which reduce the corrosion resistance and limit the possibility of forming a coated article. The paper determines the effect of the addition of 7% Si to an aluminum coating (690°C/60 s) on the microstructure thickness and type of intermediate phases as well as hardness and surface features. It has been shown that the addition of Si results in a 40 % increase in the hardness of the coating and reduce the surface roughness. In addition, is limited interdiffusion of Al and Fe, as a result of which an intermetallic phase layer is formed, Al7-9Fe2Si enriched phase, 4 times thinner than a coating without the addition of Si, while maintaining the thickness of the outer coating layer.

Protective coatings provide protection of structures against corrosion, but they also aim to meet marketing requirements – decorative qualities. One of the representatives of protective coatings are fire coatings based on Al and Al-Si, which have been used, among others, in the automotive industry. The production of Al-Si coatings using the fire method (known as: immersion) consists in immersing a previously degreased detail in a bath of molten coating metal. Al-Si coatings are applied permanently, and the connection between the coating and the substrate is ensured by the mutual diffusion of aluminum and iron, which leads to the formation of intermetallic phases. The study examines Al-Si coatings used in the automotive industry. The research included assessment of coatings in terms of structure, hardness distribution of elements, and surface condition (roughness). The chemical composition of the coatings was determined using EDX microanalysis and phase composition by diffractometric analysis. The final assessment focused on the impact of bending on the quality of the connection between the substrate and the coating.