Abstract
For the first time, high-pressure torsion (HPT) was applied to additively manufactured AlSi10Mg built in two directions (vertical and horizontal) by selective laser melting (SLM), and the influence of extreme torsional strain on the porosity, microstructure and microhardness of the alloy was investigated. ImageJ analysis indicates that significant porosity reduction is achieved by 1/4 HPT revolution (low strain). Optical microscopy (OM) and scanning electron microscopy (SEM) observations reveal the steady distortion and elongation of the melt pools, the continuous elongation of the cellular-dendritic Al matrix and breakage of the eutectic Si phase network with increased HPT revolutions. Microhardness measurements indicate that despite the significant increase in hardness attained from HPT processing, hardness saturation and microstructural homogeneity are not achieved even after 10 HPT revolutions. X-ray diffraction (XRD) line broadening analysis demonstrates increased dislocation densities with increased HPT revolutions, which contributes to the considerably higher hardness values compared to as-received samples.
Highlights
Powder bed fusion laser additive manufacturing (L-PBF AM) techniques, such as selective laser melting (SLM) and electron beam melting (EBM) have emerged as attractive methods of fabricating metallic components suitable for a wide range of applications, including automotive and aerospace
The spherical pores are known as gas-induced porosity, which could be caused by the entrapment of inert gas in the melt pool during the melting of powder or may already exist inside the initial raw powder and remain in the finished structure [68, 69]
Upon scanning a single layer of powder bed for the as-received samples built vertically (AR-V) samples, it could be more difficult for the entrapped gas to move out of the melt pool since their movement are restricted by the compact powder distribution within the layer
Summary
Powder bed fusion laser additive manufacturing (L-PBF AM) techniques, such as selective laser melting (SLM) and electron beam melting (EBM) have emerged as attractive methods of fabricating metallic components suitable for a wide range of applications, including automotive and aerospace These techniques are highly attractive because they are able to manufacture engineering components with intricate structures and tailored microstructures [1]. Various reports have suggested improvements in mechanical properties for AM-fabricated parts compared to that of their traditional counterparts, including higher yield and tensile strengths [17, 18], better corrosion resistance [19,20,21] and enhanced fatigue life [22] Such improvements are attributed to the unique and very fine microstructure as a result of rapid solidification due to the short laser-material interaction time and high cooling rates of AM processes (103–108 K s−1) [23,24,25]. The high residual stress, porosity and other defects that often exist in as-manufactured parts cause some concern, which means that some kind of post-processing, e.g. hot isostatic pressing (HIP) and heat treatment before being ready for service [26,27,28]
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