The influence of annealing temperature and time on the structure and features of the Al-Si coatings on steel sheets, purposed for pressured welded pipes applied in exhaust systems

The research results shown in the article characterize the initial state of the Al-Si coating on the steel sheet and its evolution, being an effect of the influence of the temperature and the time. The heating was carried out in different temperatures (up to 800 °C) and in different periods. After the heating, observation of the sections with the appliance of a scanning electron microscope was realized and microanalyses of the chemical composition were carried out. The state and the features of the coatings were also tested in technological tests by bumping, deep drawing, bending and expanding. The results of microhardness research, documenting structural changes, are also presented.