Ellis, Christopher Roland (2019) Additive powder manufacture of new aluminium alloys. PhD thesis, University of Warwick.

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Abstract

The research aim is identification and production of new aluminium alloys of high mechanical strength via Selective Laser Melting, and has focused on the heat-treatable 2xxx and 7xxx aluminium series. The method for selecting the alloys uses weldability as a key criterion. Laser welding deals with many of the same problems of a wide freezing temperature range leading to melt tearing and thermal gradients that SLM also has to contend with. This approach proved partially successful with all of the tested alloys achieving densities exceeding 99.2%.

For each alloy there was successful identification of a specific volumetric energy density and its component process parameters, this was conducted via a factorial DOE approach. This demonstrated the differences between the alloys examined in which SLM processing parameters they were most responsive to. A comparison between the selected alloys and their response demonstrates significant differences in response to processing even within the same alloy series.

The effect of the form of the voids within a part is examined and it was demonstrated that the form of the voids, whether they are spherical or elongated, within a material is a major factor in the overall structural integrity of the parts. It was found that form factor of the larger void population was the major correlating factor to mechanical strength rather than the overall relative volume of those voids.

This research concludes that for the production of mechanically strong aluminium alloys, Al 2618 is the one that shows the greatest promise. It demonstrated the greatest Tensile Strength of the materials tested, the most refined grain structure and had the highest consistency in those characteristics. The contribution of this research is the identification of aluminium alloys processable via SLM; the identification of ideal process conditions and the response of those materials to the SLM process. The demonstration of the effect of HIP on densifying SLM parts in these new materials, and that there is no demonstrated link between high density parts and good mechanical properties. For these alloys there is an investigation of the grain size response from SLM and post-processing, and its link to properties.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > TN Mining engineering. Metallurgy T Technology > TS Manufactures
Library of Congress Subject Headings (LCSH):	Aluminum alloys -- Testing, Aluminum alloys -- Welding, Laser welding
Official Date:	September 2019
Dates:	Date Event September 2019 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Warwick Manufacturing Group
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Gibbons, Gregory John, 1970- ; Barnes, Stuart (Professor of engineering)
Sponsors:	Progressive Technology
Format of File:	pdf
Extent:	xviii, 314 leaves : illustrations, charts
Language:	eng

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