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The fatigue resistance is a property that exerts a strong influence on the suspension spring performance in vehicles. The choice of SAE 9254 steel was due to its wide use in the manufacture of these springs and their fatigue properties and toughness. The manufacture of SAE 9254 steel springs has been made by the hot winding process and the heat treatment by conventional quenching and tempering or by cold winding process and induction hardening and tempering. The shot peening induced a compressive residual stress which increased the fatigue life of the SAE 9254 steel. The residual stress profile from the surface of springs showed a peak in the values of the compressive stress for both manufacturing processes. The maximum residual stress in the cold processed spring was higher than the hot processed spring and maintained much higher values along the thickness of the spring from the surface, resulting from manufacturing processes. The fatigue cracking of the springs, without shot peening, started by torsional fatigue process, with typical macroscopic propagation. The fracture surface showed stretch marks with high plastic deformation.

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HATTORI, Carolina S. Manufacturing, microstructural characterization, and mechanical behavior of extruded 7xxx series aluminum alloys for automotive applications, 2021. Tese (Doutorado em Tecnologia Nuclear) -Instituto de Pesquisas Energéticas e Nucleares -IPEN-CNEN/SP, São Paulo.Due to the increasingly strict legislation regarding CO2 emissions, one of the automakers' options is the use of lighter materials. This lightness issue brought even more attention to the aluminium alloys that are already widely used in the automotive industry for several applications, mainly the traditional alloys of the 5xxx and 6xxx series.In view of the industry's competitive scenario, it is necessary to develop structural alloys with high mechanical strength, such as those of the 7XXX series, which are the focus of this study. This study aims to obtain two new aluminium alloys 7108 and 7046, by extrusion, to characterize the microstructure in each stage of the manufacturing process and to analyse the mechanical behaviour in tension and fatigue. Initially, the two alloys billets were casted for further development of the extrusion process, in two different extruded profile geometries, in order to define the main process parameters and the heat treatments. The microstructures of the extruded profiles of alloys 7108 and 7046 are formed by second phase particles rich in Al-Fe-Si and fine precipitates rich in Al-Zn-Mg dispersed in an aluminium matrix. The strength limit of alloy 7046 showed a result 36% higher than alloy 7108, proving the influence of the amount of precipitates formed.For the 7046 alloy, all the maximum stress levels performed better in the fatigue properties compared to the 7108 alloy, and a significant improvement in the fatigue properties was noted due to the polishing of the specimens. On the fracture surfaces, a region with a smaller crack propagation area and a more extensive rupture region due to mechanical overload are observed. The crack propagation region is characterized by plastic deformation and the presence of striations perpendicular to the growth direction.