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. 2018 Feb 14;11(2):298.
doi: 10.3390/ma11020298.

Influence of Scanning Strategies on Processing of Aluminum Alloy EN AW 2618 Using Selective Laser Melting

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Free PMC article

Influence of Scanning Strategies on Processing of Aluminum Alloy EN AW 2618 Using Selective Laser Melting

Daniel Koutny et al. Materials (Basel). .
Free PMC article

Abstract

This paper deals with various selective laser melting (SLM) processing strategies for aluminum 2618 powder in order to get material densities and properties close to conventionally-produced, high-strength 2618 alloy. To evaluate the influence of laser scanning strategies on the resulting porosity and mechanical properties a row of experiments was done. Three types of samples were used: single-track welds, bulk samples and samples for tensile testing. Single-track welds were used to find the appropriate processing parameters for achieving continuous and well-shaped welds. The bulk samples were built with different scanning strategies with the aim of reaching a low relative porosity of the material. The combination of the chessboard strategy with a 2 × 2 mm field size fabricated with an out-in spiral order was found to eliminate a major lack of fusion defects. However, small cracks in the material structure were found over the complete range of tested parameters. The decisive criteria was the elimination of small cracks that drastically reduced mechanical properties. Reduction of the thermal gradient using support structures or fabrication under elevated temperatures shows a promising approach to eliminating the cracks. Mechanical properties of samples produced by SLM were compared with the properties of extruded material. The results showed that the SLM-processed 2618 alloy could only reach one half of the yield strength and tensile strength of extruded material. This is mainly due to the occurrence of small cracks in the structure of the built material.

Keywords: EN AW 2618; aluminum alloy; mechanical properties; relative density; scanning strategy; selective laser melting.

Conflict of interest statement

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1
Figure 1
SLM powder characteristics; (a) particle shape (SEM); (b) particle size distribution chart.
Figure 2
Figure 2
Graphical representation of used strategies; (a) layer-based approach, with rotation of scan pattern in follow up layers; (b) Meander strategy; (c) Chessboard strategy; (d) Hull and core strategy; (e) Pre sintering strategy.
Figure 3
Figure 3
Single track weld evaluation, width and height of the weld according to applied LS and LP.
Figure 4
Figure 4
Process window identified from single weld track evaluation.
Figure 5
Figure 5
Representative samples of single track weld for each group of welds; (ad) top view; (eh) cross section.
Figure 6
Figure 6
Metallography of different size cube samples fabricated using the meander strategy, top view of samples cross section (13 mm sample also shows the starting side and direction of scanning vectors in follow up layers, this was identical for all sample sizes) with relative density evaluated from the cross sections.
Figure 7
Figure 7
Influence of LP and LS variance on the defect formation using the chessboard strategy.
Figure 8
Figure 8
(a) Scanning order of individual chessboard fields for different settings of the chessboard strategy; (b) Comparison of sample defects for field-based and out-in spiral setting of the chessboard strategy; to visualize the real in size and distribution of black and white fields over the ground sample, the white fields are shown with a transparent red color.
Figure 9
Figure 9
Influence of chessboard field size on the relative porosity.
Figure 10
Figure 10
Defects in cube samples fabricated using the hull and core strategy; (a) metallography, top view of sample’s cross section; (b) dependence of relative density and laser power of the core area.
Figure 11
Figure 11
Defects in cube samples fabricated by pre-sintering strategy; (a) metallography, top view of sample’s cross section; (b) dependence of relative density and laser power.
Figure 12
Figure 12
Influence of support structure; (a) Meander strategy; (b) Chessboard strategy.
Figure 13
Figure 13
Metallography of samples with higher platform heating and meander strategy.
Figure 14
Figure 14
Metallography of samples with higher platform heating and chessboard strategy.
Figure 15
Figure 15
Microstructure of extruded material; (a) transverse direction; (b) longitudinal direction.
Figure 16
Figure 16
Microstructure of SLM state material fabricated with meander strategy; (a,c) transverse direction; (b,d) longitudinal direction.
Figure 17
Figure 17
Fraction area of tensile testing samples; (a) extruded state material; (b) SLM state material fabricated with meander strategy.
Figure 18
Figure 18
Detail of fraction area—(a) extruded state; (b) SLM state (meander).
Figure 19
Figure 19
Fraction area of tensile testing samples; (a) intermediate particles in dimples; (b) unmelted powder in pore.

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