Quantification and characterisation of porosity in selectively laser melted Al–Si10–Mg using X-ray computed tomography

• Published in: Materials characterization Vol. 111; pp. 193 - 204
• Main Authors: Maskery, I., Aboulkhair, N.T., Corfield, M.R., Tuck, C., Clare, A.T., Leach, R.K., Wildman, R.D., Ashcroft, I.A., Hague, R.J.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-01-2016
• Subjects: Additive manufacture; Aluminium alloy; ALUMINIUM ALLOYS; Aluminum; ANISOTROPY; ANNEALING; COMPUTERIZED TOMOGRAPHY; Construction; HARDNESS; HEAT; Heat treatment; LASERS; MANUFACTURING; MATERIALS SCIENCE; MELTING; MICROSTRUCTURE; NANOSCIENCE AND NANOTECHNOLOGY; Non-destructive testing; NONDESTRUCTIVE TESTING; Porosity; PRECIPITATION; PRECIPITATION HARDENING; SCANNING LIGHT MICROSCOPY; Selective laser melting; SPATIAL DISTRIBUTION; Tomography; X-ray computed tomography; X-rays; Aluminium alloy; Additive manufacture; Non-destructive testing; Selective laser melting; X-ray computed tomography
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2015.12.001

We used X-ray computed tomography (CT), microscopy and hardness measurements to study Al–Si10–Mg produced by selective laser melting (SLM). Specimens were subject to a series of heat treatments including annealing and precipitation hardening. The specimen interiors were imaged with X-ray CT, allowing the non-destructive quantification and characterisation of pores, including their spatial distribution. The specimens had porosities less than 0.1%, but included some pores with effective cross-sectional diameters up to 260μm. The largest pores were highly anisotropic, being flat and lying in the plane normal to the build direction. Annealing cycles caused significant coarsening of the microstructure and a reduction of the hardness from (114±3) HV, in the as-built state, to (45±1) HV, while precipitation hardening increased this to a final hardness of (59±1) HV. The pore size and shape distributions were unaffected by the heat treatments. We demonstrate the applicability of CT measurements and quantitative defect analysis for the purposes of SLM process monitoring and refinement.
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•We examined SLM Al–Si10–Mg with X-ray CT, microscopy and hardness measurements.•The size, shape and position distributions of the internal pores were determined.•Heat treatments alter the microstructure and hardness, but the pores are unaffected.•The largest pores are highly anisotropic, being at or disc-like in the xy plane.•CT and statistical analysis can play a role in improving the manufacturing process.