Experimental Investigation into Laser Welding of Aluminium Foam Filled Steel Tubes

Laser welding appears to be the most suitable technology for joining metallic foams. Spatially limited energy input, together with high energy density, determine a small molten material volume and a rapid solidification, which prevents the collapse of the cellular structure and the drainage phenomena. It has indeed already been shown that laser welding is a useful technique for joining metal foam panels with conventional or foamable filler. The welding techniques were also widely applied and studied for the Aluminum Foam Sandwich (AFS). Composite materials obtained by filling with metallic foam hollow profiles are nowadays available. Reliable welding processes have to be carried out in order to realize complex lightweight structures. The present paper investigates the butt-joint laser welding of a composite material made of steel tubes filled with aluminum foam core. Two pieces of a metal foam filled steel tube were prepared by chamfering the edge and foamable filler was then inserted between them. The process was divided in two parts. As a first phase of the method, the joining of the tubes was obtained by tuning the laser parameters in order to weld the whole tube thickness without damaging the metal foam. Finally, the laser beam was used in order to obtain both a sort of heat treatment in the tubes material and a temperature gradient inside the aluminum foam core. In this second stage of the laser processing, the beam parameters were tuned in order to achieve the foaming temperature inside the tubes. The hollow steel profiles were filled up with aluminum powder precursors, which were produced by cold uniaxial compaction according to the powder metallurgical route. They were then foamed in a furnace. A Laser machining center with 3 kW CW FAF CO2 laser source and five CNC axes was used. This study is a preliminary step in order to verify the reliability of the method, and further investigations will be necessary with the aim of optimizing the process. The present investigation was limited to laser beam power and process speed. At the present stage the results are very encouraging and a prototype has therefore been constructed.