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Fatigue is the main cause of mechanical failure in aircraft structures, in which aluminum alloys are employed in approximately 70% of their structural components. Among the microstructural characteristics of aluminum alloys, the hardening precipitates provided by the ageing heat treatment have an important influence in their mechanical properties. In this context, current studies have shown that the two-step ageing heat treatment (T6I4) improves the mechanical properties of 6xxx and 7xxx aluminum alloys. This investigation presents a study of high cycle fatigue behavior of aluminum alloys AA 6351 (T6 and T6I4) and AA 7050 (T7451 and T6I4) as well the influence of microstructural characteristics and two-step ageing heat treatment in the fatigue properties of these alloys. Fatigue tests were performed on smooth and notched specimens.

The medium carbon steel and low alloy SAE 4340 has undergone several changes in this development process came 300M steel, from this ultra-high strength steel. With similar resistance and higher ductility to the steel 300M, the maraging steel can replace conventional steels in various applications. This study aims to evaluate and compare the microstructure and mechanical strength of SAE 4340 steel, 300M and Maraging 18Ni 300, underwent the procedure of autogenous laser welding.

Due to their favorable properties, among them the excellent strength-to-weight ratio, aluminum alloys are applied in transport vehicles, like trucks and buses. With respect to their mechanical behavior, fatigue is a process that alters the life of a structural component producing local stresses and floating strains and consequently giving rise to crack nucleation and the fracture of the material. In this work it is shown the influence of microstructure and intermetallic particles in aluminum alloy AA6005-T6, AA6063-T6 and AA6351-T6 that were tested for tension and fatigue. The microconstituents and the crack path on the fracture surfaces were analyzed by optical microscopy and scanning electron microscopy (SEM). The variation of the geometry of the precipitated particles of Mg₂Si, intermetallics (Fe,Mn)₃SiAl₁₂ and irregular distribution of particles in the matrix of the alloys were observed.

In the present work, two HSLA steels are evaluated as candidates to replace the current SAE 1010 steel in the manufacture of trucks and buses wheel rims. Since the welding process is a critical stage of the production of these parts, samples were taken from flash-welded blanks of the chosen steels in order to provide information on the microstructure and mechanical behavior of the weld and heat-affected zones and compare them to the conventional SAE1010 steel. The mechanical properties were evaluated by means of hardness, tensile and impact tests. The obtained results provide support for the understanding on how the welding process affects the materials' properties and give important information related to the conventional steel replacement towards a significant weight reduction of the component.

The aim of the present work is to analyse the microstructural changes caused by distinct heat treatments and their relationships with the mechanical properties of a recently developed microalloyed steel with 0.08%C-1,5%Mn. This steel, designated as B550, is being considered as a promising alternative to replace the low carbon steel in some wheel`s components for the automotive industry. Various multiphase microstructures with different amounts of ferrite, martensite, bainite and retained austenite were obtained by means of heat treatments conducted at distinct temperatures. Tensile tests allowed evaluating the mechanical properties of the various material conditions. The experimental results showed that water quench from 800°C results in a better combination of mechanical properties of strength, hardenability and ductility.