Effect of Heat Treatment Prior to Direct Hot-Extrusion Processing of Al–Cu–Li Alloy

Abstract

This study presents and explains the results of the first steps in developing high strength aluminium alloy (Al–Cu–Li) wires for the ultimate purpose of using them as feedstock for DED (directed energy deposition) techniques, such as wire arc additive manufacturing (WAAM). Powder metallurgy (PM) is proposed as the method to produce the wires due to the high flexibility to adapt the composition and the lower temperatures used with respect to casting. Two PM routes are proposed. The first route comprises blending of the powders, uniaxial pressing, and hot extrusion of the green compact to obtain a bar; the second route includes a heat treatment of the green compact, to promote the diffusion of the alloying elements before hot extrusion. Further steps, such as rolling or drawing, are necessary to obtain the wire from the bar. This work studies the effects of the processing parameters on the properties of extruded bars and compares the results of the two routes employed, with special attention paid to the effects of heat treatment. The study confirms that heat treatment homogenises the microstructure and requires higher applied extrusion force and time. The results from characterisation show the presence of Al–Cu and Al–Cu–Li phases in the microstructure.

Keywords

• hot-extrusion
• powders
• heat treatment
• Al–Li alloys