Additive Manufacturing: Solid-State Phase Transformations and Microstructural Evolution: Aluminium Alloys
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: High Temperature Alloys Committee, TMS: Phase Transformations Committee
Program Organizers: Bij-Na Kim; Andrew Wessman, University of Arizona; Chantal Sudbrack, National Energy Technology Laboratory; Eric Lass, University of Tennessee-Knoxville; Katerina Christofidou, University of Sheffield; Peeyush Nandwana, Oak Ridge National Laboratory; Rajarshi Banerjee, University of North Texas; Whitney Poling, General Motors Corporation; Yousub Lee, Oak Ridge National Laboratory
Thursday 8:30 AM
March 18, 2021
Room: RM 5
Location: TMS2021 Virtual
Session Chair: Whitney Poling, General Motors; Andrew Wessman, The University of Arizona
8:30 AM Invited
Connecting Microstructure Evolution to Mechanical Behavior of an Al-Mn-Sc Alloy Designed for Selective Laser Melting: Fan Zhang1; Qingbo Jia2; Xinhua Wu2; 1National Institute of Standards and Technology; 2Monash University
Laser-based additive manufacturing features a nonequilibrium fabrication process. Its inherent variations in the directionality and magnitude of thermo-mechanical strain and temperature gradients lead to formation of heterogeneous microstructures and nonuniform mechanical properties. Understanding the connection between microstructure evolution and mechanical behaviors through post-build heat treatment is critical for alloy optimization. We performed comprehensive structure characterization using ex situ scanning/transmission electron microscopy, atom-probe tomography, and in situ synchrotron-based small angle X-ray scattering and X-ray diffraction to investigate the precipitation kinetics of an Al-Mn-Sc alloy specifically designed for selective laser melting. We observed simultaneous and continuous nucleation and growth of two types of precipitates at distinct length scales and evaluated their effects on mechanical properties acquired by tensile testing. We identified a pseudo-delay nucleation and growth phenomenon for the strengthening nanoscopic Al3Sc precipitates, attributable to intrinsic heat treatment induced by layer-by-layer fabrication of additive manufacturing. [1] Acta Materialia, (193) 239-251, 2020.
9:00 AM
Characterization and Simulation of Eta and Eta-prime Precipitates Evolution in Laser Heat Treated Cold Spray of AA7050: Ning Zhu1; Luke Brewer1; 1University of Alabama
This presentation describes the evolution of eta and eta-prime precipitates during laser heat treatment of aluminum alloy AA7050. The size and distribution of metastable eta-prime precipitates dominate the mechanical property of AA7xxx alloys. Wrought plates and cold sprayed AA7050 material were subjected to systematic laser heat treatments. These thermal profiles were used in combination with ThermoCalc and PRISMA simulations to simulate the evolution of the eta and eta-prime phases. The results predict that eta precipitates are mainly distributed along the grain boundaries, while eta-prime are primarily nucleated within the grain matrix. Transmission electron microscopy is being employed to quantify the precipitate sizes, volume fractions, and spacing in the starting cold spray powders, cold spray deposits, and comparison wrought plates. We observed coarsening of both eta and eta-prime precipitates in the cold spray deposits. The degree of coarsening is a strong function of the linear heat input employed during laser heating.
9:20 AM
Possibilities for Replacing Scandium in High Strength Al-Mg Alloys for 3D Printing by Transition Metal Alloying: Viktor Mann1; Roman Vakhromov2; Dmitriy Ryabov2; Vladimir Korolev2; Daria Daubarayte2; Maria Grol2; Alexander Seferyan2; Kirill Nyaza2; 1RUSAL Management; 2Light Materials and Technologies Institute
Al-Mg alloys for 3D printing, alloyed with strengthening elements, have advantages for application in various industries (automotive, aviation and space, tooling and consumer goods) due to their attractive levels of mechanical characteristics and corrosion resistance. Scandium remains the most effective additive in aluminium alloys, increasing the yield strength and the material processability. However, Sc is an expensive alloying element which addition in the amount of 0.1% wt. increases the total cost by at least 2 times.In the present work the scientific approaches for development of Al-Mg based materials for using in laser powder bed fusion (LPBF), economically alloyed with Sc, as well as with full replacement of Sc are presented. The advanced analysis of mechanical properties and corrosion behavior was carried out. The specific features of structure formation were discussed. The opportunities to use topological optimization, LPBF-process modeling to design new parts for various applications are presented.
9:40 AM
Solidification Structure Characterization of an AlCuMnZr Alloy with respect to geometric features and Multiple Parameters: Kevin Sisco1; Sumit Bahl2; Matthew Chisholm2; Richard Michi2; Jonathan Poplawsky2; Amit Shyam2; Ryan Dehoff2; Alex Plotkowski2; Suresh Babu1; 1University of Tennessee Knoxville; 2Oak Ridge National Lab
As the understanding of additive manufactured parts continues to grow, and the library of alloys is expanded, there is a need for more careful consideration of the interplay from the fundamental solidification effects and post processing heat treatments. In this study, we examine 49 different parameter sets across a range of geometric features to investigate the sensitivity of the as-fabricated microstructure and properties. The wide variety of samples in addition to a high preheat temperatures of 200°C, allows the formation of Theta Prime during a build that can eliminate a post heat treatment step. In addition, post processing heat treatments are used to prevent the stabilizing precipitates (Theta Prime) from coarsening and transforming into Theta. These results are used to outline future directions for the optimization of process parameters as a function of geometry and heat treatments and will allow for more opportunities to control site specific microstructural distributions.
10:00 AM
Effects of Thermal Processing on the Microstructure and Mechanical Properties of Additively Manufactured AlSi10Mg Parts: John Fite1; Suhas Prameela2; John Slotwinski1; Timothy Weihs2; 1Jhu Applied Physics Lab; 2Johns Hopkins University
The Powder Bed Fusion (PBF) process is used for the additive manufacturing (AM) of metal parts and is capable of producing a wide variety of complex and intricate components. For AlSi10Mg, thermal post-processing is crucial to achieve the full range of material properties. This work focuses on the effects of thermal post-processing on AlSi10Mg microstructural evolution. AM AlSi10Mg coupons were fabricated by PBF, then were thermally treated using a conventional approach (with a Solution Heat Treatment (SHT)), and an alternative approach adapted for AM (without a SHT). Micro-tensile specimens were cut by EDM, and ductility and tensile strength were measured, with the alternative annealing approach resulting in superior tensile strength. Microstructural differences are correlated to tradeoffs in mechanical properties and deformation mechanisms.
10:20 AM
Evolution of Microstructure and Dispersoids in Al-Mg 5xxx Alloys Under Wire + Arc Additive Manufacturing and Permanent Mold Casting: Kun Liu1; Ahmed Algendy1; Jianglong Gu2; X. Grant Chen1; 1University of Quebec at Chicoutimi; 2Yanshan University
In the present work, the evolution of microstructure and dispersoids in Al-Mg 5xxx alloys under wire + arc additive manufacturing (WAAM) and permanent-mold casting (PM) has been characterized and compared with the aid of optical microscopy and scanning/transmission electron microscopy. In the as-cast/as-deposited condition, the grains and intermetallics are much finer while the microhardness is much higher in WAAM sample than PM sample. However, during the heat treatment, the formation of dispersoids in WAAM sample is slower with bigger size and lower volume, leading to its lower final micro-hardness than PM sample after 425oC/24h. Besides, the area fraction of dispersoids zone in WAAM sample is lower than PM sample, especially at relative lower heat-treatment temperature (~ 375oC). The formation and distribution of dispersoids during various heat treatments have been characterized and quantified aiming to discover the influence of fabrication methods (PM and WAAM) on the precipitation behavior of dispersoids.
10:40 AM
Effect of Laser Glazing on Powder-Processed Icosahedral-Phase-Strengthened Aluminum Alloys: From Single Track to Overlapping Tracks: Mingxuan Li1; Hannah Leonard1; Sarshad Rommel1; Cain Hung1; Thomas Watson2; Tod Policandriotes3; Rainer Hebert1; Mark Aindow1; 1University of Connecticut; 2Pratt & Whitney; 3Collins Aerospace
Recently, we have developed a series of Al-Cr-Mn-Co-Zr alloys that exhibit a nano-composite FCC Al matrix plus I-phase dispersoid microstructure in gas-atomized powders, and which is retained during consolidation to form bulk materials. Here, laser glazing experiments have been performed to evaluate the potential of the alloys for use in metal additive manufacturing (MAM). Laser tracks were produced on the surfaces of polished coupons at a range of laser powers and scanning speeds, and the resultant microstructures and properties were evaluated using electron microscopy studies and hardness measurements. At an appropriate combination of processing parameters, the FCC Al + I-phase microstructure was retained, resulting in elevated hardness values. Further experiments were performed using overlapping melt tracks, which more closely represent the conditions that would prevail in MAM. These results will be reviewed, and the potential for developing new alloys for MAM based on such systems will be discussed.