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The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. ABSTRACTSelective laser melting (SLM) of aluminium is of research interest because of its potential benefits to high value manufacturing applications in the aerospace and automotive industries. In order to demonstrate the credibility of SLM Al parts, their mechanical properties need to be studied. In this paper, the nano-, micro-, and macro-scale mechanical properties of SLM AlSi10Mg were examined. In addition, the effect of a conventional T6-like heat treatment was investigated and correlated to the generated microstructure.Nanoindentation showed uniform hardness within the SLM material. Significant spatial variation was observed after heat treatment due to phase transformation. It was found that the SLM material's microhardness exceeded its die-cast counterpart. Heat treatment softened the material, reducing micro-hardness from 125±1 HV to 100±1 HV. An ultimate tensile strength (333 MPa), surpassing that of the die cast counterpart was achieved, which was slightly reduced by heat treatment (12 %) alongside a significant gain in strain-to-failure (~threefold). Significantly high compressive yield strength was recorded for the as-built material with the ability to withstand high compressive strains. The SLM characteristic microstructure yielded enhanced strength under loading, outperforming cast material. The use of a T6-like heat treatment procedure also modified the properties of the material to yield a potentially attractive compromise between the material's strength and ductility making it more suitable for a wider range of 1 E-mail: nesma.aboulkhair@nottingham.ac.uk 2 applications and opening up further opportunities for the additive manufacturing process and alloy combination.

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Metal components with applications across a range of industrial sectors can be manufactured by selective laser melting (SLM). A particular strength of SLM is its ability to manufacture components incorporating periodic lattice structures not realisable by conventional manufacturing processes. This enables the production of advanced, functionally graded, components. However, for these designs to be successful, the relationships between lattice geometry and performance must be established. We do so here by examining the mechanical behaviour of uniform and graded density SLM Al-Si10-Mg lattices under quasistatic loading. As-built lattices underwent brittle collapse and non-ideal deformation behaviour. The application of a microstructure-altering thermal treatment drastically improved their behaviour and their capability for energy absorption. Heat-treated graded lattices exhibited progressive layer collapse and incremental strengthening. Graded and uniform structures absorbed almost the same amount of energy prior to densification, 6.3 ± 0.2 MJ/m 3 and 5.7 ± 0.2 MJ/m 3 , respectively, but densification occurred at around 7% lower strain for the graded structures. Several characteristic properties of SLM aluminium lattices, including their effective elastic modulus and Gibson-Ashby coefficients, C 1 and α, were determined; these can form the basis of new design methodologies for superior components in the future.

Selective laser melting (SLM) is being widely utilised to fabricate intricate structures used in various industries. Widening the range of applications that can benefit from such promising technology requires validating SLM parts in load bearing applications. Recent studies have mainly focussed on static loading, with minor attention to cyclic loading despite its vital importance in many applications.In this work, the fatigue performance of SLM AlSi10Mg was investigated considering the effects of surface quality and heat treatment. Compared to heat treatment, machining the samples played a minor role in improving the fatigue behaviour. This is potentially attractive to industries interested in latticed structures and topology-optimised parts where post-processing machining is not feasible. The characteristically fine microstructure in the as-built samples provided good fatigue crack propagation resistance but none of them survived nominal fatigue life of 3x10 7 cycles within the maximum stress range of 63-220 MPa. A specially-tailored heat treatment increased the material's ductility, significantly improving its fatigue performance. At 94 MPa, the heat-treated samples survived beyond the nominal fatigue life, outperforming the reference cast material. The combined effect of machining and heat treatment yielded parts with far superior fatigue properties, promoting the material for a wider range of applications.

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Precipitation hardening of selective laser melted AlSi10Mg was investigated in terms of solution heat treatment and aging duration. The influence on the microstructure and hardness was established, as was the effect on the size and density of Si particles. Although the hardness changes according to the treatment duration, the maximum hardening effect falls short of the hardness of the as-built parts with their characteristic fine microstructure. This is due to the difference in strengthening mechanisms.