Aluminium alloy development for Additive Manufacturing

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&lt;0.7wt% or Si+2/3Mg&gt;4wt% for Mg &lt; 3wt% and Si &gt; 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.2023-04-18 The thesis was published2023-04-25 The number in the series was found to be incorrect in the printed version. The number was corrected in the online version. The PDF was up to this date hav been downloaded 32 times.Further funding:Norsk Hydro ASA</p

High-Throughput Printability Screening of AlMgSi Alloys for Powder Bed Fusion

The importance of both recycling and additive manufacturing (AM) is increasing; however, there has been a limited focus on the development of AM alloys that are compatible in terms of recyclability with the larger scrap loops of wrought 5xxx, 6xxx and cast 3xx aluminium alloys. In this work, the powder bed fusion (PBF) printability of AlMgSi alloys in the interval of 0-30 wt% Mg and 0-4 wt% Si is screened experimentally with a high-throughput method. This method produces PBF-mimicked material by PVD co-sputtering, followed by laser remelting. Strong evidence was found for AlMgSi alloys being printable within two different composition ranges: Si + Mg &amp;lt; 0.7 wt% or for Si + 2/3 Mg &amp;gt; 4 wt% when Mg &amp;lt; 3 wt% and Si &amp;gt; 3 wt%. Increasing the amount of Mg and Si influences the grain structure by introducing fine columnar grains at the melt pool boundary, although the melt pool interior was unaffected. Hardness in an as-built state increased with both Mg and Si, although Si had a neglectable effect at low levels of Mg. Both the evaporative loss of Mg and the amount of Mg in solid solution increased linearly with the amount of Mg

A novel rapid alloy development method towards powder bed additive manufacturing, demonstrated for binary Al-Ti, -Zr and -Nb alloys

Powder bed fusion (PBF) methods offer the best material properties among metal additive manufacturing (AM) processes. Yet, alloy development for PBF is only at its infancy and has a great untapped potential. This originates from the high solidification rate within the melt pool and to exploit the full potential of materials produced by PBF methods, a diligent work lies ahead. This paper presents a high-throughput method to rapidly screen large compositional alloy intervals experimentally for their PBF feasibility, which can drastically reduce the time needed for alloy development and provide valuable data for modelling. Our method consists of two steps; co-sputtering and electron beam re-melting. First step produces an alloy gradient film on a sheet substrate. The film is then re-molted to produce a PBF mimicked microstructure. The method is successfully demonstrated on binary systems; Al-Ti,-Zr and-Nb and produced gradients in compositional ranges of 3-50 wt%Ti, 1-15 wt%Zr and 2-15 wt%Nb over a length of 200 mm. From the produced materials, the alloying efficiency could be investigated and determined regarding hardness and grain refinement. Zr shows the highest strength contribution per at% and the best grain refinement at low levels. However, at higher levels grain refinement efficiency decreases for Zr. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).Funding Agencies|Norsk Hydro ASA; Carl Tryggers Foundation for Scientific Research [CTS 15:219, CTS 14:431]</p

Investigation of Ti-1_x(Zr,Ta,V,W)(x)B-2 and A(l3)Ti(1_x)(Zr,V)(x) grain refiners in additively manufactured Al-2 wt%Cu alloys by a high throughput method

Grain refinement plays a central role in powder bed fusion (PBF) additive manufacturing by preventing hot cracking and thus enabling the development of high-strength alloys. However, the mechanism behind grain refinement is not fully understood for conventional casting, nor for PBF. In this work, a high throughput method have been used to produce Al-2 wt%Cu alloys with additions of Ti1-xM(Zr,Ta,V,W)(x)B-2, Al3Ti1-xM(Zr,V)(x) or AlB2 grain refiners for 0.1 &amp;lt; x &amp;lt; 0.9. It was found that grain size varied with x, M and the sum of Ti + M. Ti1-xMxB2 grain refiners offered no advantage over Al3Ti1-xMx. Overall, Ti and Zr provide the best grain refinement, both as Ti1-xMxB2 and Al3Ti1-xMx. However, Ti1-xZrxB2 had a grain refinement minimum around x = 0.65-0.70. The behavior was similar with Ta, but to a lesser extent. V and W had detrimental effects on grain refinement. Despite the fact that no AlB2 particles were observed, additions of B provided excellent grain refinement and was more efficient than Ti below 0.5at%. Ti1-xMxB2 lattice parameters varied with x and followed Vegards law, however, a clear relationship between grain size and epitaxial strain/lattice match could not be established. Similarly, the growth restricting factor alone was not a predictor of grain size.Funding Agencies|Norsk Hydro ASA; Centre in Nanoscience and Technology at LiTH. Carl Tryggers Foundation for Scientific Research [CTS 14:431]; AMEXCI AB; [CTS 15:219]</p