Effects of Alloy Composition and Solid-State Diffusion Kinetics on Powder Bed Fusion Cracking Susceptibility
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Effects of Alloy Composition and Solid-State Diffusion Kinetics on Powder Bed Fusion Cracking Susceptibility Holden Hyer1 • Le Zhou1 • Abhishek Mehta1 • Yongho Sohn1
Submitted: 7 July 2020 / in revised form: 17 September 2020 / Accepted: 12 October 2020 Ó ASM International 2020
Abstract Laser powder bed fusion (LPBF) has demonstrated its unique ability to produce customized, complex engineering components. However, processing of many commercial Al-alloys by LPBF remains challenging due to the formation of solidification cracking, although they are labelled castable or weldable. In order to elucidate this divergence, solidification cracking susceptibility from the steepness of the solidification curves, specifically |dT/df1/2 S |, as the fraction solidified nears 1 towards complete solidification, was calculated via Scheil–Gulliver model as a function of solute concentration in simple binary Al-Si, AlMg, and Al-Cu systems. Introduction of ‘‘diffusion in solid’’ into Scheil–Gulliver model resulted in a drastic reduction in the cracking susceptibility (i.e., reduction in the magnitude of 1/2 |dT/df1/2 S |) and a shift in the maximum |dT/dfS | to higher concentrations of solute. Overall, the calculated solidification cracking susceptibility correlated well with experimental observation made using LPBF AA5083 (e.g., AlMg) and Al-Si binary alloys with varying Si concentration. Cracking susceptibility was found to be highly sensitive to the composition of the alloy, which governs the variation of |dT/df1/2 S |. Furthermore, experimental observation suggests that the contribution of ‘‘diffusion in solids’’ to reduce the cracking susceptibility can be more significant than what is expected from an instinctive assumption of
& Yongho Sohn [email protected] Holden Hyer [email protected] 1
Department of Materials Science and Engineering, Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, FL 32816
negligible diffusion and rapid cooling typically associated with LPBF. Keywords additive manufacturing aluminum alloy cracking susceptibility diffusion laser powder bed fusion
1 Introduction Additive manufacturing (AM) has demonstrated repeated success in producing customized components, previously restricted by the limitations of subtractive manufacturing via traditional materials processing methods.[1–3] Laser powder bed fusion (LPBF) is a popular AM technique that has shown to produce dense, complex parts, built by repeated melting of a powder bed with a laser source in a layer by layer process.[1–3] Unfortunately, LPBF of certain Al-alloys such as high strength AA7075 and corrosion resistant AA5083 is limited by the extensive formation of solidification cracking and/or excessive porosity.[4–7] Predominantly, Al alloyed with near eutectic compositions of Si, * 12.6 wt.%,[8] such as Al-10 wt.% Si-0.5 wt.% Mg (known as AlSi10Mg), have had success with building crack-free parts with LPBF.[9–11] AlSi10Mg was adopted from casting as the high concentration of Si decreases the vis
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