Since the need for the joining of dissimilar materials is increasing, the wide range of requirements of the numerous industries would lead to the development of new welding techniques or at least to improvement of the existing technologies capable of joining the components from the miniature assemblies to extremely large earth-moving vehicles. Among the different materials, iron-based alloys and aluminum-based alloys are the most significant materials that are finding applications in the various industries to offer more viable and sustainable products. However, welding of these metals has been always a kind of dilemma for the engineers. There are a certain number of methods to join these dissimilar metals but no one could establish a reliable or a sort of credible welding method for the industrial applications while quality, cost, human resources and facilities are taken into the main considerations. This paper reviews the recent works on the joining of different aluminum alloys to different steels. The effect of the joining conditions on the formation of intermetallics and microstructural development, mechanical properties and applications of the joints are discussed.

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17-4 PH stainless steel has wide applications in severe working conditions due to its combination of good corrosion resistance and high strength. The weldability of 17-4 PH stainless steel is challenging. In this work, hybrid laser-arc welding was developed to weld 17-4 PH stainless steel. This method was chosen based on its advantages, such as deep weld penetration, less filler materials, and high welding speed. The 17-4 PH stainless steel plates with a thickness of 19 mm were successfully welded in a single pass. During the hybrid welding, the 17-4 PH stainless steel was immensely susceptible to porosity and solidification cracking. The porosity was avoided by using nitrogen as the shielding gas. The nitrogen stabilized the keyhole and inhibited the formation of bubbles during welding. Solidification cracking easily occurred along the weld centerline at the root of the hybrid laser-arc welds. The microstructural evolution and the cracking susceptibility of 17-4 PH stainless steel were investigated to remove these centerline cracks. The results showed that the solidification mode of the material changed due to high cooling rate at the root of the weld. The rapid cooling rate caused the transformation from ferrite to austenite during the solidification stage. The solidification cracking was likely formed as a result of this cracking-susceptible microstructure and a high depth/width ratio that led to a high tensile stress concentration. Furthermore, the solidification cracking was prevented by preheating the base metal. It was found that the preheating slowed the cooling rate at the root of the weld, and the ferrite-to-austenite transformation during the solidification stage was suppressed. Delta ferrite formation was observed in the weld bead as well no solidification cracking occurred by optimizing the preheating temperature.

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