Aluminum Alloys, Processing and Characterization: New and Optimized Aluminium Alloys I
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Dmitry Eskin, Brunel University

Tuesday 8:30 AM
February 25, 2020
Room: 1A
Location: San Diego Convention Ctr

Session Chair: Shouxun Ji, Brunel University London


8:30 AM Introductory Comments

8:35 AM  
Effect of Cooling Rate During Solidification of Aluminium-chromium Alloy: Gautham Muthusamy1; Samuel Wagstaff2; Antoine Allanore1; 1Massachusetts Institute of Technology; 2Novelis Inc.
    Controlling the distribution of alloying elements in aluminum casting and designing new processing practices are supported by an enhanced understanding of the thermodynamics and kinetics of solidification at industrial scales. While the behavior of eutectic forming elements such as copper is well understood, the interactions of peritectic-forming elements such as chromium have received far less attention. Insights and limitations of nucleation models pertinent to industrially-observed cooling rates are explored. This is realized by calculation TTT diagrams using a time dependent nucleation theory. This demonstrates the significance of cooling rates on phase selection in industrially relevant technologies like DC casting and Twin roll casting. To improve future predictions, A possible route to measure thermodynamic and kinetics properties is suggested, for accurate determination of these time dependent nucleation models.

9:00 AM  
Effects of Si Content on the Conductivity, Microhardness, Microstructure and Hot Tearing of Al-0.8Fe-0.5Mg-0.4Ni Alloys: Stephanie Kotiadis1; Adam Zimmer1; Abdallah Elsayed1; Eli Vandersluis2; C. Ravindran2; 1University of Guelph; 2Ryerson University
    Electrified automotive powertrain systems require new Al alloys with high castability and high thermal and electrical conductivity. This research presents the effects of Si on the thermal and electrical conductivity, microhardness, and microstructure of Al-0.8Fe-0.5Mg-0.4Ni-xSi alloys. The Al-Fe-Mg-Si-Ni alloys were prepared by mixing pure Al, Fe, and Ni, as well as Al-50 wt.% Mg and Al-50 wt.% Si master alloys at 730°C with varying amounts of Si (0.15-0.45 wt.%). The alloys were characterized using optical and electron microscopy, x-ray diffraction, fluidity testing, microhardness testing and electrical/thermal conductivity measurements. The microstructure contained Chinese script Al-Fe-Si phases when no Ni was present, globular Al-Fe-Ni-Si with the addition of Ni, as well as Mg-Si phases. These phases, in combination with Mg solute added significant hardness to the alloys. The Al-Fe-Mg-Ni-Si alloys showed the necessary high fluidity, high conductivity, and high hardness for use in next-generation automotive powertrains.

9:25 AM  
The Efficacy of Replacing Metallic Cerium in Aluminum-cerium Alloys with LREE Mischmetal: Zachary Sims1; David Weiss2; Orlando Rios3; Hunter Henderson3; Michael Kesler3; Scott McCall4; Michael Thompson1; Aurelien Perron4; Emily Moore4; 1University of Tennessee; 2Eck Industries; 3Oak Ridge National Laboratory; 4Lawrence Livermore National Laboratory
    The ongoing development of aluminum-cerium alloys has produced materials exhibiting elevated high temperature mechanical property retention, long term microstructural stability, and flexible processability compared to traditional aluminum alloys, accommodating the growing demand for high temperature aluminum alloys not requiring the use of high-cost elements like scandium. To date, reported Al-Ce alloy compositions contain large amounts of elemental cerium. Mischmetal (MM), a mixture of lanthanum, cerium, and other light rare earth elements (LREE) is less expensive and more available than pure cerium. The chemical similarity of the LREEs means there is possibility to use MM as the primary alloy addition, lowering alloy cost. This talk will report the effect of using MM in place of cerium in a 12 wt% binary alloy on mechanical properties, phase constituency, thermal stability, and load sharing. Results will show that MM can be substituted completely for cerium with a mostly positive impact on alloy performance.

9:50 AM  
Effects of Sc and Y on the As-cast Microstructure of AA6086: Sandi Zist1; Varuzan Kevorkijan1; Matej Steinacher1; Franc Zupanic2; Irena Paulin3; Matjaz Godec4; 1Impol d.o.o.; 2Faculty of Mechanical Engineering; 3Institute for Metals and Technology; 4Institute of Metals and Technology
    AA6086 is a novel Al-Mg-Si alloy that contains 0.15–0.25 wt. % Zr and more Si and Cu than AA 6082. This new alloy is distinguished by its improved tensile strength and hardness and useful ductility. Additions of rare-earth elements can further improve these properties. In order to clarify their influence, we prepared several alloys containing either individual or combined additions of Sc and Y in the range 0.21.0 % Sc, 0.11.0 % Y . The alloys were melted and then cast into a copper mould. The alloys were investigated by optical microscopy, SEM with EDS, and XRD. There are several microstructural constituents in the as-cast state. Larger additions of Sc (1 wt. %) strongly increased the grain size number, up to 7.5 G. In the centre of the crystal grains were Al3(Sc,Zr) particles, which are effective grain refiners. The grain-refinement effects were minor when we used Y.

10:15 AM Break

10:30 AM  
Ternary Interactions and Implications for Third Element Alloying Potency in Al-Ce-Based Alloys: Hunter Henderson1; David Weiss2; Zachary Sims1; Michael Thompson3; Emily Moore4; Aurélien Perron4; Fanqiang Meng5; Ryan Ott5; Orlando Rios1; 1Oak Ridge National Laboratory; 2Eck Industries, Inc.; 3University of Tennessee, Knoxville; 4Lawrence Livermore National Laboratory; 5Ames Laboratory
    The recently developed class of Al-Ce-based alloys offer a number of beneficial attributes, including high temperature strength retention, resistance to microstructural coarsening, and excellent castability. Binary alloys around the eutectic composition of ~11 wt.% Ce contain a characteristic large volume fraction of eutectic Al11Ce3 lathes. However, further alloying additions to improve properties can stabilize a myriad of ternary Al-Ce-X phases that complicate alloying efficacy in unexpected ways, as intermetallic stability often changes between solidification and solutionizing temperatures. Unlike in many Al alloys that can be solution treated to a single phase, Al-Ce and Al-Ce-X intermetallics form during solidification and their morphology is largely retained during heat treatment, similarly to composite materials. This morphological stability remains even after stoichiometric changes. Here, we present design principles for Al-Ce-based alloys, especially with Si, Cu, and Mg additions. Changes to alloying element strengthening potency, empirical models, and integration with CALPHAD databases will be discussed.

10:55 AM  
Development and Analysis of Al7075 Alloy Materials using Press and Sinter Processing: Steven Johnson1; Corey Clark1; Jason Alvarez1; 1Central Connecticut State University
    The high strength, precipitation hardening Aluminum alloy 7075 (Al7075) is a desirable structural material due to low density, high strength to weight ratio, and ease of fabricability. In this work, near shape press and sinter processing of premixed and prealloyed Al7075 powders are compared. Both premixed and gas atomized prealloyed Al7075 powders were consolidated using room temperature closed die compaction followed by controlled atmosphere sinter densification. Starting powders were characterized for morphology, size distribution, hardness, and phase constituents. Both premixed and prealloyed powders were compacted at stresses up to 600 MPa using add mixed and die wall lubricants. Sinter densification was performed in inert and semi-inert atmospheres with sintering temperatures guided by thermal analysis. The resultant materials were characterized for density, microstructure, phase development, hardness, and hardening response. This work is intended to advance press and sinter processing of high strength Al alloys in powder form for potential structural applications.

11:20 AM  
Retrogression Forming and Reaging of AA7075-T6 Alclad to Produce Stampings with Peak Strength: Katherine Rader1; Louis Hector2; Jon Carter2; Eric Taleff1; 1University of Texas at Austin; 2General Motors
    A retrogression heat treatment was combined with simultaneous warm forming to produce cross-shaped stampings from AA7075-T6 Alclad sheet. This process is termed retrogression forming. A maximum allowed retrogression forming time, which includes sheet heat up, transfer, and stamping, was defined to achieve peak-aged strength through a single reaging heat treatment after forming. Sheets of 1.6-mm-thick AA7075-T6 Alclad were stamped at 200°C to a depth of 45 mm within 2 seconds without splitting. The formed geometry exhibits a complexity appropriate to automotive structural components. These stampings were then subjected to one of two reaging heat treatments. A full reaging heat treatment of 120°C for 24 hours produced strength levels in excess of the original, peak-aged T6 alloy sheet. A simulated paint bake heat treatment at 185°C for 25 minutes recovered 95% of the strength lost during warm forming.