Studying Porosity, Structure Morphology and Mechanical Characteristics of the Products Obtained by Selective Laser Melting of the AlSi10Mg Alloy Powder

Аuthors

Brykin V. A.^*, Ripetskii A. V.^**, Korobov K. S.^***

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: benbrykin@yandex.ru
**e-mail: a.ripetskiy@mail.ru
***e-mail: korobovks@mai.ru

Abstract

The current level of manufacturing technologies development, the additive manufacturing from metal powders by Selective Laser Melting (SLM) in particularl, allows obtaining high production functional products with unique properties. However, the expanding range of materials and SLM equipment leads to prolonged cycles of technological work in search for optimal process parameters and increases the production cost. Additive manufacturing plays an important role in the aviation and space-rocket industry. Time reduction on experimental cycles of R & D helps accelerating implementation of additive technologies and reduce product cost. It stipulates the necessity of the technological procedures and experiments funnel automation.
The presented study examines an experiment on elementary volumes melting of the cubes (cube samples) and identification of optimal SLM process parameters for the AlSi10Mg powder in terms of porosity, sample microstructure morphology and mechanical characteristics obtained under the specified technological parameters. The issue of the software component development for the samples express analysis, allowing determining automatically the most solid samples and technological parameters sets corresponding to them was considered additionally.
The metal powder composition for the study was AlSi10Mg alloy powder produced by the OK RUSAL company. The samples were manufactured ин the Addsol D50 installation, with the control routine developed with the MAI developed “PKTPP” software complex. The metallographic samples were prepared with the equipment from the Struers company. The samples porosity study was being conducted with the Nordson DAGE NT500 XD7600NT Ruby X-ray computer tomography installation. The samples microstructure was studied as well with the TFS Quattro S scanning electron microscope (SEM).
The authors proposed a layout solution, allowing synthesize 120 sample-cubes with the wide variation of the SLM process parameters in a single run of the Addsol D50 installation. The proposed solution allows significant acceleration of the process (up to 200%) of the volumetric samples synthesis on the installations with the small plot area (up to 50mm).
A software component for the express analysis of the cube sample porosity , based on the images obtained through the X-ray computer tomography (RCT) was developed with the Python language and tools from the libraries such as Scikit-image (skimage), Matplotlib, and Seaborn. The program receives a set of “raw” images from the RCT installation, processes each image computing the volume of voids and discontinuities of each layer, and then computes the total volume of pores/discontinuities in the sample, determining thereby the sample relative density.
For the samples with minimal porosity, a microstructure study was conducted with the SEM to analyze the metallographic section of these samples. The least porous samples (with relative density of 99.5% and higher), manufactured with the minimum layer height (30 µm), exhibit a homogeneous dendritic-cellular microstructure. The average grain size does not exceed 1-2 µm, which, combined with the slight grain orientation in the direction of sample growth, indicates relatively high strength of the items manufactured under the corresponding parameters, as confirmed by tensile test results. 
Parameters of the SLP technological process [325 W, 900 mm/s, 30 um] for achieving the uniform fine grained microstructure (1-2 μm), as well as relative density of the samples of 99.7%, tensile limit of 341.5 MPa and relative elongation of 2.65% were determined for the studied metal-powder composition of the AiSi20Mg alloy with the developed software component and domestic Addsol D50 installation.
Elemental composition maps of the studied sections for a series of samples were obtained. Results of the mechanical tensile tests of the samples manufactured according to selected technological parameters have been aduced, with a comparison of mechanical properties and SLM process parameters.
It is assumed that the total time reduction of the R & D cycle of additive manufacturing by the proposed means of express analysis of experimental results will allow faster transition to the process of high-tech products serial additive manufacturing in high-performance sectors of industry (such as aviation and aerospace industries).

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