The Effect of Stress Relief on the Mechanical and Fatigue Properties of Additively Manufactured AlSi10Mg Parts

Mfusi Mfusi,Popoola Popoola,Tshabalala Tshabalala,Mathe Mathe

doi:10.3390/met9111216

Mfusi Mfusi, Popoola Popoola + Show 2 more

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https://doi.org/10.3390/met9111216

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Abstract

The heating and cooling profiles experienced during laser additive manufacturing results in residual stresses build up in the component. Therefore, it is necessary to perform post build stress relieving towards the retention and improvement of the mechanical properties. However the thermal treatments for conventional manufacturing do not seem to completely accommodate these rapid heating and cooling cycles of laser processing techniques such as powder bed fusion. Characterizations such as density measurements on the samples were performed employing the Archimedes principle; hardness testing was performed on the Zwick micro/macro (Hv) hardness tester, SEM and Electron backscatter diffraction (EBSD). Fracture toughness and crack growth was conducted on a fatigue crack machine. All characterization was done after stress relieving of Selective Laser Melting (SLM) produced samples at 300 °C for 2 hrs was performed in a furnace. The mechanical properties appear to be rather compromised instead of being enhanced desirably. As-built SLM produced tensile specimens built in different directions exhibited significantly favorable mechanical properties. However, post stress relieve thermal treatment technique deteriorated the strength while increasing the ductility significantly. Nonetheless, fatigue crack growth and fracture toughness illustrated positive outcome in terms of fatigue life on SLM produced AlSi10Mg components in application.

Highlights

Additive manufacturing (AM) is a new technology that has made its mark as an innovative and flexible manufacturing technology [1]
The study was carried out on specimens produced by the Selective Laser Melting (SLM) Solution M280 GmbH from Lubeck in Germany using a laser power of 150 W, 1000 mm/s scan speed, 50 μm hatch spacing and 50 μm powder layer thickness fixed processing parameters
The results of this work substantiated the anisotropy, which is the demonstration of different mechanical properties in different axis, in SLM produced tensile samples even post stress relief

Summary

Introduction

Additive manufacturing (AM) is a new technology that has made its mark as an innovative and flexible manufacturing technology [1]. The additive manufacturing of aluminum alloys in particular finds recent applications in the aerospace, rail and automotive industries for structural and non-structural parts, which are usually die casted. The powder bed fusion processing of aluminum alloys has gained interest in the aerospace, rail and automotive industries due to the versatile nature of the process. Low stress requirements are often the objective for these components relative to stressful loading circumstances where finite-life fatigue resistance should be considered as distinctively possible such as circumstances where load or vibrations counteracting on component could be extreme [4]. Fatigue resistance crack propagation relative to the direction of the load is inherently dependent to anisotropy of the process of manufacturing. It is Metals 2019, 9, 1216; doi:10.3390/met9111216 www.mdpi.com/journal/metals

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