Effects of Laser-Powder Bed Fusion Process Parameters on the Microstructure and Corrosion Properties of AlSi10Mg Alloy

Abstract

In this study, the effects of microstructural modifications induced by tuning the laser-powder bed fusion (L-PBD) process parameters on electrochemical stability of the L-PBF-AlSi10Mg alloy are investigated. Three groups of L-PBF-AlSi10Mg samples were fabricated utilizing combinations of L-PBF process parameters for their Upskin layers. The implemented process parameters modifications were found to be not only effective in reducing the as-printed surface roughness of the components, but also led to the formation of cyclic small-large melt pools (MPs) in Upskin layers of the fabricated samples. Such consecutive modification in the size of MPs led to the increased inhomogeneity of the microstructure, contributing to the formation of a coarser intercellular eutectic-Si network, larger grain size, and lower density of low angle grain boundaries. Among all fabricated samples, the sample that experienced the fastest cooling during solidification was found to reveal the highest corrosion resistance and the best passive film stability on its Upskin surface both in naturally-aerated and deaerated 3.5 wt.% NaCl electrolyte, owing to the finer Al-Si eutectic structure that forms along its large MP-boundaries. The as-printed microstructure of the L-PBF-AlSi10Mg was found a dominant factor in determining the necessity of applying post-printing surface polishing procedures to attain better corrosion properties.

The Electrochemical Behavior of As-Prepared Aluminum Alloy A360 Produced by Selective Laser Melting Fabrication with and without a Trivalent Chromium Process Conversion Coating

“…34,35 The micrograph of the X-Z surface shows the characteristic layering morphology characteristic of SLM fabrication. [6][7][8][9][10][11][12][13][14]41 The layer-to-layer and melt tracks visible are stacked to form good metallurgical bonding. In this micrograph, the boundaries of the melt pool are visible with a few identified by dashed lines.…”

“…The micrograph (X-Y) of the build surface more clearly reveals the elongated cellular network typical of A360 prepared by SLM. [6][7][8][9][10][11][12][13][14]41 Based on published work, the cells consist of Al grains surrounded by a hexagonal network of Si phase. [6][7][8][9][10][11][12][13][14]41 The coarse grains seen in the micrograph for the X-Y plane are several hundred micrometers in long dimension.…”

“…This is a common difference between cast and SLM prepared alloys. 4,12,42,43 The absence of these segregated particles reduces the number of galvanic couples present on the SLM alloy and generally leads to better corrosion resistance of the SLM as compared to the cast alloy. 4,12,31,42,43 Specimen texture and morphology of TCP-coated alloy specimens.-Figure 6A presents a series of scanning electron micrographs of a TCP-coated A360 alloy.…”

“…4,12,42,43 The absence of these segregated particles reduces the number of galvanic couples present on the SLM alloy and generally leads to better corrosion resistance of the SLM as compared to the cast alloy. 4,12,31,42,43 Specimen texture and morphology of TCP-coated alloy specimens.-Figure 6A presents a series of scanning electron micrographs of a TCP-coated A360 alloy. The alloy was abraded, polished, degreased, deoxidized, and immersion coated with TCP at room temperature for 10 min In the center of the micrograph in Fig.…”

“…In the family of aluminum alloys, A360 (AlSi 10 Mg) is the one most often prepared by AM methods. [6][7][8][9][10][11][12][13][14] The traditional method for preparing this alloy is by die casting. There has been some published work describing the microstructure and mechanical strength of A360 alloys prepared by SLM in comparison with die-cast materials, but comparatively little research has been reported on the electrochemical behavior of these SLM alloys as-prepared and after surface finishing with coating systems.…”