The influence of hydrothermal carbonization of sisal fibers on the mechanical properties of composites based on recycled polypropylene matrices was investigated in this paper. The fibers were characterized by X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The composites, with short fibers randomly distributed, processed by extrusion and injection processes, were characterized using quasi-static tensile and impact mechanical tests and scanning electron microscopy. The hydrothermal carbonized sisal fibers, proved by Fourier-transform infrared spectroscopy analysis, besides increasing the material's crystallinity, caused a larger adherence on the interface fiber/polymer matrix as verified in the scanning electron micrographs. The addition of 10% and 20% of 2 h hydrothermal carbonized sisal fibers treatment produced a composite with, respectively, an increase of 17.9% and 32.2%, on the modulus of elasticity, of 9.25% and 52.3% on the resistance to impact and of 19.06% and 29.85% on yield strength, in comparison to the recycled polypropylene. The hydrothermal carbonization technique changed the concept of recycling the polypropylene allowing new applications to the produced materials due to its mechanical properties.

Aluminum alloys are not covered by their specific weight. Each class of aluminum alloy presents a set of properties that are favorable to a given function in the same product, just as the alloys may be present in the same vehicle. However, it is necessary to know the changes in the mechanical properties that occur with the union process of these aluminum alloys. The objective of this study was to evaluate the mechanical and morphological properties of alloys 5383 H34, 5754 H34 and 6005 T6 similarly welded and dissimilar by the MIG process. Six combinations of these alloys were characterized by mechanical tensile, folding and Vickers micro-hardness tests, as well as scanning electron microscopy (SEM) and optical microscopy (OM). Among the results obtained, a decrease in tensile strength was observed for all welded alloys. In addition, the microhardness was affected in the melt line, in the weld bead and in the HAZ (heat affected zone). The main causes of the reduction of the mechanical resistance of the welded alloys were the grain growth and the precipitate dissolution. The data obtained in this study contribute in a very positive way to the development and dimensioning of new projects and technologies involving aluminum alloys.