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High strength low-alloy (HSLA) steels have been employed in the automotive industries to produce chassis, part of suspensions, and truck wheels, among others. They present good strength and mechanical toughness, in addition to good formability and weldability. However, good weldability depends on the welding process and parameters. For mechanical components with occurrence of cracks, fatigue life can be quantified by the fatigue crack growth stage. This paper aims to evaluate the fatigue crack growth in HSLA steel plates welded by flash butt welding and laser beam welding. The different welding processes and welding parameters used resulted in their distinct microstructures. The different microstructures showed significant differences in hardness; however, they showed no significant differences in fatigue crack growth. Moreover, the weld beads showed higher resistance to fatigue crack growth when compared to the base metal. For cracks propagating across the weld beads obtained by laser beam welding, with crack initiating at the base metal and growing toward the heat-affected zone and weld bead, a drop in the fatigue crack growth rate was observed as the crack tip approached the microstructure gradient found between these regions. [ABSTRACT FROM AUTHOR]

The effects of operational conditions on dissimilar Al-Cu flash welded joint quality have been studied using a series of industrial welding experiments. Macro- and microstructural analyses of dissimilar aluminum-copper joints produced by flash butt welding are performed in the present work. Various process conditions including standard and non-standard operational conditions were assessed during the welding experiments. Optical and scanning electron microscopy and electron dispersive x-ray spectroscopy are used to investigate and assess the metallurgical joints created through this process. For suboptimal process conditions, voids (5 mm wide, 1 mm deep) were observed at the joint interface. Some of the voids contained remnants of molten metal while some were empty. Al-Cu intermetallic compounds at the joint area were investigated, and their chemical compositions are determined. The profile of the joint interface was observed to be wavy which is attributed to the voids on the copper side and insufficient material flow of the copper during the upset. The effects of welding parameters on the waviness of the interfaces are investigated. The results show that the waviness of the interface increases with increasing the heat intensity (heat/joint area). No correlation was observed between the flashing speed and the waviness of the interfaces. [ABSTRACT FROM AUTHOR]

A 400 MPa ultra-fine grain steel possesses high strength and toughness. Due to its fine grain size, the heat affect zone (HAZ) of the weld joint will soften during welding. The weldability of 400 MPa ultra-fine reinforced steel bar of flash butt welding is investigated by using the micro metallographical examination and macro-mechanical-property tests. The joint of flash butt welding has a superior mechanical property. The HAZ in the weld joint does not show apparent softening. There is only a localized softening spot inside the weld seam, which does not affect the property of the whole joint. Therefore, flash butt welding is appropriate for joining the 400 MPa ultra-fine grain reinforced steel bars. The resulting weld joint has excellent mechanical properties. [ABSTRACT FROM AUTHOR]