Aluminium alloy development for Additive Manufacturing

Abstract: Powder Bed Fusion (PBF Additive Manufacturing AM have emerged as a promising manufacturing process possessing a powerful combination of characteristics. Most noticeable are the near-net-shape, short lead time and flexibility, both with regard in design freedom and in part-to-part variation. Aluminium alloys are used in everything from food packaging, furniture's, to cars and airplanes. To accommodate for this wide range in material requirements, different alloys have been developed over the past century. To reach the full potential of AM, a thoroughly work lies ahead of the research community to find, tailor and refine alloys.This work has focused on experimentally screening of AM alloys, for their printability and potential properties. To accelerate this, a novel high through put method was first developed to efficiently produce a broad range of alloys both with respect to compositions and alloying elements. This method consists of two steps; in the first step a compositional alloy gradient film is deposited on an aluminium substrate, and in a second step a microstructure mimicking PBF is formed by either laser or electron beam melting of the film. Gradients up to 500mm in length ranging from 0-85wt% in alloying content were achieved. This enabled high resolution studies of the influence of alloying elements over wide compositional intervals. Various aspects of the material were possible to investigate such as: Grain size, hardness, printability, evaporation losses, solid solution, electrical conductivity and microstructure. The results were verified against the available literature, and a strong correlation between properties of the PBF mimicked materials and actual PBF materials were confirmed.With the developed screening method, printability i.e. the material's capacity to be processed in PBF without formation of cracks , could be studied and mapped out for a large set of alloys. The AlMgSi system were found to be printable without grain refinement if Si+Mg<0.7wt% or Si+2/3Mg>4wt% for Mg < 3wt% and Si > 3wt%. Investigations of Til-xMxB2 and Al3Til-xMx grain refiners in 2wt% Cu alloys reveled that grain refinement and printability strongly correlated to both x and the element M(Zr,Ta,V,W). However, no clear relationship between the grain size and the lattice parameters of Til-xMxB2 and Al3Til-xMx were found.In addition to mapping out printability, hardness as a function of composition was also mapped out for the binary alloys Al -Ti, -Zr, -Nb, -Sr and the AlMgSi system. Other important findings are that the Mg loss due to evaporation and the solid solution of Mg was found to depend linearly on the amount of Mg, and a transition from equiaxed to fine lamellar Al4Sr intermetallic going above 5wt%. Altogether, the screening method developed in this work offer a unique way to efficiently study composition dependent transitions in printability, microstructure and other material properties which are otherwise difficult to foresee or experimentally laborious to study.