Microstructural Characterization of the Anisotropy and Cyclic Deformation Behavior of Selective Laser Melted AlSi10Mg Structures

Abstract

The laser-based fusion of metallic powder allows construction of components with arbitrary complexity. In selective laser melting, the rapid cooling of melt pools in the direction of the component building causes significant anisotropy of the microstructure and properties. The objective of this work is to investigate the influence of build anisotropy on the microstructure and mechanical properties in selective laser melted AlSi10Mg. The alloy is comprehensively used in the automotive industry and has been one of the most frequently investigated Al alloys in additive manufacturing. Using specimens produced in three different building orientations with respect to the build platform, the anisotropy of the microstructure and defects will be investigated using scanning electron microscopy and microcomputed tomography. The analysis showed a seven-times higher pore density for the 90°-specimen compared to the 0°-specimen. The scanning electron microscopy revealed the influence of the direction of the cooling gradient on the constitution of the eutectic phase. Mechanical properties are produced in quasi-static and fatigue tests of variable and constant loading amplitudes. Specimens of 0° showed 8% higher tensile strength compared to 90°-specimens, while fracture strain was reduced almost 30% for the 45°-specimen. The correlation between structural anisotropy and mechanical properties illustrates the influence of the building orientation during selective laser melting on foreseen fields of application.

In Situ SEM Study of the Micro-Mechanical Behaviour of 3D-Printed Aluminium Alloy

“…The issue of Young's modulus is more challenging to understand for aluminium alloys since these materials are almost elastically isotropic, so that the directional dependence of stiffness cannot be explained by texture variation. However, it should be noted that, similarly to our results, it has been shown that Young's modulus varies significantly within the range of 63-72 GPa for SLM 3D-printed AlSi 10 Mg alloy [31].…”

“…[28] and Tang M. [29] investigated an AlSi 10 Mg alloy and achieved the same results as in our study; namely, samples manufactured in the vertical direction (Z-X) showed higher values of ultimate tensile strength than specimens built in the horizontal direction (X-Y). However, there are other studies where samples printed with equal conditions and composition demonstrated the inverse relation [30,31]. Moreover, this stochastic behaviour of mechanical characteristics was found during tensile tests of samples with other alloy compositions such as AlSi 10 , A356 (AlSi 7 Mg 0.3 ) and A357 (AlSi 7 Mg 0.7 ) [27].…”

Corrosion of metallic materials fabricated by selective laser melting

“…The anisotropy in the SLMed parts is usually caused by the different solidification rates in different directions, and heat conductivity in the building direction (z-axis) is typically faster than that in the other two spatial directions (x-and y-axes) due to the high-heat transfer efficiency of the pre-deposited metals. [121][122][123] The microstructural anisotropy in the SLMed parts usually leads to anisotropic mechanical properties [124][125][126] and corrosion behaviours. 127,128 For the mechanical properties, there was a larger elongation along the building direction than in the other two spatial directions due to the grain growth mainly occurring along the building direction, such as for stainless steels and CoCrW alloys.…”

Investigation of the anisotropic cyclic damage behavior of selective laser melted AISI 316L stainless steel

“…15 A possible nondestructive test method to identify and characterize the process-induced porosity is the use of Xray computed tomography (CT). The method is widely used for different AM materials such as aluminum [16][17][18] and titanium alloys 19,20 for density measurements and characterization of pores and cracks. However, steels are challenging for X-ray applications due to their high density, high absorption coefficient, and the effect of beam hardening, causing artifacts and noise in the CT data.…”