Additive Manufacturing of Metals: Microstructure, Properties and Alloy Development: Al-based Alloys
Program Organizers: Prashanth Konda Gokuldoss, Tallinn University of Technology; Jurgen Eckert, Erich Schmid Institute of Materials Science; Zhi Wang, South China University of Technology
Monday 2:00 PM
October 10, 2022
Room: 302
Location: David L. Lawrence Convention Center
Session Chair: Adriana Eres-Castellanos, Colorado School of Mines; Tim Gabb, Nasa Glenn Research Center
2:00 PM
Regional Mechanical Performance and the Effects of Surface Defects in AM Al-10Si-Mg: Thomas Ivanoff1; Nathan Heckman1; Andrew Polonsky1; Kyle Johnson1; 1Sandia National Laboratories
Additively manufactured (AM) components can provide mass savings and production agility when used in structural applications for a multitude of fields. The variable mechanical behavior of AM metals can lead to uncertainties in performance that are challenging to account for during design. Uncertainty in performance can arise from build parameters, stochastic variability across builds, and differences in microstructure. Mechanical performance can also vary spatially within individual components. This study focuses on the mechanical behavior along the exterior regions, approximately 150 micrometers deep, of an Al-10Si-Mg AM alloy and how failure propagates from this exterior region. High-fidelity microstructural characterizations were combined with in-situ computed tomography during uniaxial-tensile testing to evaluate properties along exterior surfaces. The observed mechanics were incorporated directly into reduced order meshing techniques that can account for specific properties along the exterior of AM materials into models. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
2:20 PM
Crystallographic Relationships between the Prior-beta Structure and Precipitate Phases in Additively Manufactured Nickel Aluminum Bronze: Dillon Watring1; Colin Stewart2; Richard Fonda2; David Rowenhorst2; 1National Research Council Research Associateship at Naval Research Laboratory; 2Naval Research Laboratory
Metal additive manufacturing (AM) has become a vital tool in numerous industries. Recently, wire arc additive manufacturing (WAAM) has become popular for applications of large components due to the high deposition rate and low equipment costs compared to other metal AM techniques. One specific alloy, nickel aluminum bronze (NAB), has been valued for its high strength, corrosion resistance, and cavitation resistance. Although WAAM techniques have shown advantages over traditionally cast components, there is a large amount of uncertainty surrounding the processing-structure-property relationships in WAAM metals. Specifically, when rapidly cooled, NAB produces a fine, face centered cubic (fcc) alpha phase from a coarse high-temperature body centered cubic (bcc) beta phase, along with various kappa precipitates. This work investigates the reconstructed prior beta grains in WAAM NAB while retaining the microscopy resolution necessary to resolve the fine alpha phases and precipitates and the influence of WAAM processing parameters on the microstructural features.
2:40 PM
Laser-Stirred Powder Bed Fusion of High Strength Aluminum Alloys: Alber Sadek1; 1Edison Welding Institute
Recently, much of the focus in developing AM processes has been towards producing fully dense and crack-free deposits that make epitaxial deposits with the texture oriented parallel to the build direction. Through the AM process, as build microstructure has the potential to be controlled to produce functionally equiaxed microstructure and crystallographic texture throughout an AM part that, in theory, could perform better under complex mechanical loadings than epitaxial microstructure. A new era of engineering design is possible with crystallographic texture control combined with equiaxed, fine grain microstructure as materials engineering concepts. Within this work, a demonstration of microstructure control and mechanical properties through the variations in the scan strategy by laser stirring was illustrated for A205 and AlSc alloys. Both alloys were successfully deposited crack-free with high density and more refined as build microstructure using stirred hatches compared with linear hatches.
3:00 PM
Multi-scale Microstructural Characterization of Additively Manufactured 7050 Aluminum Alloy Subjected to Post-processing Treatments: Rupesh Rajendran1; Crosby Owens2; Jeffrey Eisenhaure2; David Spain2; Preet Singh1; 1Georgia Institute of Technology; 2Northrop Grumman Corporation
7xxx series aluminum alloy fabricated via laser powder bed fusion (LPBF) process has a huge potential in the aerospace industry due to inherent benefits associated with the additive manufacturing (AM) process and a combination of high-strength, light-weight properties. Inoculant or nanoparticle addition has been shown to promote equiaxed grain growth in these alloys, mitigating hot tearing and solidification defects associated with the columnar grain structure, which limited their adoption. This work presents a modified AM 7050 aluminum alloy having an equiaxed grain structure with minimal defects. Multi-scale characterization using a combination of OM, DSC, SEM, and TEM is done to understand the microstructural features and their correlation with the post-processing treatments such as stress relieving, HIPing and artificial aging. Comparison of results with an equivalent wrought alloy gives insights on post-processing optimization for achieving target properties.
3:20 PM Break
3:40 PM
Microstructure Development and Creep Resistance of Selective Laser Melted Al-Fe-Mn-Si-Zr Alloy: Jovid Rakhmonov1; Nhon Vo2; Joseph Croteau2; Joshua Dorn2; David Dunand1; 1Northwestern University; 2NanoAL LLC
Phase transformations during solidification and subsequent aging of selective laser melted (SLM) Al-Fe-Mn-Si-Zr alloy (Addalloy HT alloy from NanoAL) are investigated using SEM, S/TEM and 3D-APT. Its mechanical properties are assessed at 20 and 300 °C via hardness and creep testing, respectively. Microstructural investigations reveal a bimodal grain structure, with ultrafine equiaxed grains at melt pool bottom and coarser, columnar grains at melt top/center. Grain boundaries throughout the melt pool are extensively decorated by α-Al(FeMn)Si precipitates formed during solidification, and the grain interiors exhibit L12-Al3Zr nanoprecipitates formed upon aging. This complex grain/precipitate microstructure allows for both excellent room-temperature strength and outstanding creep resistance. The creep resistance of Al-Fe-Mn-Si-Zr is compared to other cast and SLM Al alloys in both diffusional and dislocation creep regimes, and it is rationalized by considering the role of precipitates in (i) preventing grain-boundary sliding, (ii) inhibiting dislocation movement and (iii) providing load sharing with α-Al.
4:00 PM
Al Nanoparticle inside Si Grain of Al-Si Alloy by Powder Bed Fusion Using an Electron Beam: Kenta Ishigami1; Kenta Aoyagi2; Huakang Bian2; Akihiko Chiba2; Yoshiki Hashizume3; Akiei Tanaka3; 1Toyo Aluminium K.K. and Tohoku University ; 2Institute for Materials Research, Tohoku University; 3Toyo Aluminium K.K.
Microstructure refinement of Al-Si alloy is needed for improving mechanical property. In casting of Al-Si alloy, additives like Sr or TiB2 are used for microstructure refinement. Additive manufacturing can refine microstructure of Al-Si alloy without additives because of superheating and rapid cooling. Additive manufacturing using electron beam is attractive for Al alloy due to its high absorptivity of electron beam. Therefore, we have investigated properties of Al-Si alloy made by powder bed fusion using an electron beam in detail. As a result, microstructure of the Al-Si alloy depended on the position along the building direction. Scanning transmission electron microscopy analysis revealed that Al nanoparticles formed in Si grains. The number density of fine particles also depended on the position along the building direction.
4:20 PM
The Effects of Post-Weld Processing on Friction Stir Welded Additive Manufactured AlSi10Mg: Michael Eff1; Harvey Hack2; 1EWI; 2Northrop Grumman
Given the limited build volumes of additive manufacturing (AM) machines, a method of combining AM with traditional manufacturing methods is needed. Welding of AM components is a solution to this challenge. This study investigated the feasibility of using friction stir welding (FSW) to join powder-bed-fusion laser (PBF-L) AlSi10Mg and examined the effects of industry standard post weld processing techniques. The samples which underwent a post-weld annealing heat treatment had cracking outside of the stir zone. The crack contained evidence of liquation near single-phase Si despite the annealing temperature being 27°C (49°F) below the reported solidus temperature. The annealing heat treatment was in the partial liquation regime for AlSi10Mg per CALPHAD simulations. The voids and crack formation mechanisms were caused by equilibrium liquation coupled with the unique microstructure and stress state. FSW was determined to be a feasible method of joining PBF-L printed aluminum alloys with minimal knock-down in tensile strength.
4:40 PM
Evaluation of a Quasicrystal-Reinforced Al Alloy as a Candidate for Additive Manufacturing: Baris Yavas1; Cain J. Hung1; Mingxuan X. Li1; S. Pamir Alpay1; Mark Aindow1; 1University of Connecticut
Metal additive manufacturing (MAM) has attracted intense interest for a wide variety of industrial applications. Most early studies used powder-processed versions of conventional alloys for MAM, but researchers have now started to investigate many different novel candidate alloys. One of the more material types that is under consideration for MAM is quasicrystal (QC) reinforced metal matrix composites (MMCs). In this study, we evaluated an Al-Cu-Fe-Cr alloy, which contains a dispersion of icosahedral QCs; these hard dispersoids serve as reinforcements in the FCC Al matrix giving composite strengthening. We performed laser-glazing of solid samples in a powder bed laser fusion MAM system. Single laser tracks were formed on the solid sample using a wide range of laser powers and scan speeds. Electron microscopy (SEM, FIB and TEM) studies revealed the formation of I-phase dispersoids in all of the laser tracks, indicating excellent potential for use of this alloy in MAM.
5:00 PM
Microstructure and Mechanical Properties of Laser Powder Bed Fusion Aluminum Matrix Composite Reinforced with Al2O3 Nanofibers: Babak Alinejad1; Amir Mostafaei1; 1Illinois Institute of Technology
High-strength aluminum matrix composite (AMC) reinforced with Al2O3 nanofibers was additively manufactured by laser powder bed fusion. We aim to establish a process window to produce high-density, defect-free AMC made of aluminum powder premixed with an in-lab synthesized Al2O3 nanofibers. Role of process parameters such as laser power, scan speed, hatch space, and scan strategy as well as fraction of reinforcement are investigated on densification, defects such as porosity and cracking, metal/oxide interface and possible segregation. We show at an optimum ratio of Al matrix to Al2O3 nanofibers and process parameters, the nano-additives result in a pinning effect in the developed AMC that enhance the strength, hardness, and wear resistance. We demonstrate that the improved performance is related to a high density of well-dispersed nanofibers, strong interfacial bonding between Al matrix and nanofibers, and ultrafine grain structure of the LPBF processed AMC.
5:20 PM
Aluminum Matrix Composites Reinforced with Multi-walled Carbon Nanotubes and C₆₀ Manufactured by Laser Powder Bed Fusion: Sangmin Yoo1; Se-Eun Shin1; 1Sunchon National University
We prepared Al/C₆₀ and Al/MWCNT composites under 25 different conditions to observe their microstructure and mechanical property trends according to laser power and scan speed. The relative density of LPBFed composites increased as the energy density increased due to the oxide layer present on the aluminum surface and the high laser reflectance. It was found that, as the energy density increased, the increase in nanohardness and elastic modulus of the LPBFed composites was due to the high relative density. However, the high laser power condition of 179 W resulted in the softening of materials due to grain coarsening, resulting in a decrease in nanohardness and elastic modulus. Under the same laser conditions, the nanohardness of the LPBFed Al/2 vol.% MWCNT composites was approximately 0.5 GPa higher than that of the LPBFed Al/1 vol.% C₆₀ composites, which is explained by the high relative density and grain refinement strengthening.