Aluminum Alloys, Characterization and Processing: Casting and Solidification
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Julie Levesque, Quebec Metallurgy Center; Stephan Broek, Kensington Technology Inc

Wednesday 8:30 AM
March 22, 2023
Room: 32A
Location: SDCC

Session Chair: X.-Grant Chen, University of Quebec at Chicoutimi


8:30 AM  
Fundamental Study on Modified Solidification of 1370 and AlSi7 with and without Commercial Grain Refiners: Robert Fritzsch1; Amund Ugelstad1; Henrik Gobakken1; Silje Li1; Shahid Akhtar2; Lars Arnberg1; Ragnhild Aune1; 1Norwegian University of Science and Technology (NTNU); 2Hydro Aluminium AS
    The microstructure of aluminium (Al) and its alloys is a well-investigated key parameter utilised to adjust their mechanical, chemical, and physical properties. The microstructure of Al can be altered by several processes, such as controlled solidification rate, grain refiner additions, and external force fields. The present study has chosen to focus on conventional procedures for grain refinement and compare the results to new low-energy concepts. In view of this, five different commercial grain refiners (2 different AlTi3B1, AlTi5B1, AlB3 and AlTi3C0.15) were added to lean 1370 and AlSi7 aluminium alloys at (i) different solidification rates, and (ii) influenced by alternating electromagnetic fields. The results were evaluated based on the effects on grain size and electrical conductivity. The initial results revealed an inverse relationship between the conductivity and the final grain size, which also proved to be independent of the origin of the refined grain structure.

8:55 AM  
Improving the Mechanical Properties of Cast Aluminum via Ultrasonication-induced Microstructural Refinement: Katherine Rader1; Jens Darsell1; Jon Helgeland1; Nathan Canfield1; Timothy Roosendaal1; Ethan Nickerson1; Adam Denny1; Aashish Rohatgi1; 1Pacific Northwest National Laboratory
    One barrier to the broader use of cast aluminum alloys in automotive applications is their poor mechanical properties, especially compared to wrought materials. This study investigates the use of ultrasound to refine the microstructure of cast aluminum alloys during solidification and thus improve their mechanical properties. A 356 aluminum alloy (Al-Si-Mg) with added Fe (to mimic a recycle-grade alloy) was cast in a graphite mold with the simultaneous application of ultrasound. Tensile specimens were extracted from the castings and heat treated to a T6 temper. Ultrasonication during casting transformed the primary aluminum grains from dendritic grains ~150 microns in size to globular grains ~30 microns in size. Ultrasonication during casting increased the ultimate tensile strength by 20 % compared to casting without ultrasound. This improvement in strength demonstrates the potential for ultrasound to improve the performance of cast aluminum alloys without altering alloy chemistry or additional post-processing.

9:20 AM  
Microstructural Changes on the Al−Cu−Si Ternary Eutectic Alloy with Different Cooling Rates: Seunghwan Oh1; Youngcheol Lee1; 1Korea Institute of Industrial Technology
    In order to understand its solidification behavior and microstructural evolution of Al−Cu−Si ternary eutectic alloy, microstructural changes of a ternary Al−Cu−Si eutectic alloy with different cooling rates were investigated. Thermodynamic analysis of the alloy system showed that the equilibrium solidification of the ternary eutectic alloy followed three stages− precipitation of primary Si phase, evolution of binary eutectic Si+Al2Cu and the formation of ternary eutectic Al+Al2Cu+Si. In order to investigate the microstructure of the alloy with rapid cooling, the mold preheated temperature was controlled. With higher cooling rates, a bimodal microstructure, which is composed of eutectics with different length scale, were developed. However, it is practically difficult to implement rapid cooling in the foundry industry. Therefore, a study on the microstructural modification of Al−Cu−Si ternary eutectic alloy under the normal casting conditions is conducted and the results are investigated in this study.

9:45 AM  
Nanoparticle-enhanced Arc Welding of Aluminum Alloys: Narayanan Murali1; Xiaochun Li1; 1University of California, Los Angeles
    Arc welding high strength aluminum alloys is a great challenge due to characteristic defects upon melting and re-solidification. However, it is an economical method by which these important engineering alloys can be processed. An emerging metallurgical technique known as nano-treating has seen increasing use in tandem with classical metallurgy, with the latest advances being presented here. Incorporating a small volume fraction of nanoparticles into the welding process significantly alters associated structure/processing/property relationships and enables the joining of difficult-to-weld aluminum alloy systems. From a structural perspective, nanoparticles disallow the formation of dendrites and attenuate large secondary phases that are seen in conventional arc welding, thus eliminating hot cracking. The microstructural evolution that nanoparticles permit along with traditional strengthening mechanisms elevates the performance of the weld over its traditional barriers. Thus, the nano-treating approach paves the way for new possibilities in arc welding high-strength aluminum alloys and other “unweldable” systems.

10:10 AM Break

10:25 AM  
Phase Equilibria in Al-Fe Alloys: Jozef Medved1; Maja Voncina1; Joze Arbeiter1; 1University of Ljubljana
     Solidification of aluminium alloys is a complex process in which inhomogeneities form. Aluminium and iron form the equilibrium phase Al13Fe4 and various metastable intermetallic phases: Al6Fe, AlmFe, AlxFe. Four alloys were prepared and analysed in the laboratory: AlFe1, AlFe1Si0.1, and AlFe1Si0.5. Thermodynamic calculations, differential scanning calorimetry, electrical resistivity measurements, optical and scanning electron microscopy were used to analyse the alloys.The results show that the addition of silicon to the AlFe1 alloy has a great influence on the distribution, amount and morphology of the phases formed during the solidification process. The addition of 0.1 wt.% Si reduces the amount of metastable Al6Fe phase. The transformation sequence was defined, starting with the dissolution of the metastable phase and the nucleation of the stable phase Al13Fe4. Due to the increased diffusion lengths of the iron atoms, the transformation takes place in the eutectic range after 4 hours of homogenization at 600 °C.

10:50 AM  
Secondary Phase Refinement in Molten Aluminum via Low Power Electric Current Processing: Jonathan Goettsch1; Aaron Gladstein1; David Weiss2; Ashwin Shahani1; Alan Taub1; 1University of Michigan; 2Eck Industries
    Metal matrix composites offer improved mechanical properties at a reduced weight compared to monolithic alloys. The reinforcing capabilities of the particulate are dependent on their size, distribution, and bonding with the matrix. The intermetallic compound, Al3Ti, has excellent bonding with the surrounding matrix but can grow detrimentally large with extended hold times in the molten state. Depending on the processing condition and with varying levels of silicon, very different morphologies of the Al3Ti are observed. In addition, passing electrical current at low power levels through the melt has been found to reduce the size of the Al-Ti intermetallic phase by inducing fracture. This research focuses on the novel processing method of passing an electric current through molten aluminum alloy to refine the reinforcing secondary phase. This technique could have broad impacts on particulate refinement in multiple metal matrix composite systems.

11:15 AM  
Fluidity and Microstructural Analysis of Al-Ni Alloys with Varied Ni Concentrations: Vigneshwar Hari1; Dong Xu1; Stuart McDonald1; Zherui Tong1; Dongdong Qu1; Kazuhiro Nogita1; 1The University of Queensland
    The manufacturing associated with emerging technologies, including electric vehicles, is impacting demand for cast aluminium alloys, including those based on the Al-Ni system. These alloys typically have a eutectic with a fine lamellar spacing in the as-cast condition, display high thermal stability, high electric conductivity, resistance to hot tearing, good fluidity, and strength. These properties combined make this alloy system suitable for a variety of applications. This research investigates the effect of varying the concentration of Ni on the solidification mode, microstructure, and fluidity of Al-Ni alloys. Hypoeutectic, eutectic, and hypereutectic compositions of Al-Ni from 0 to 10wt.% were investigated, and it was found that hypereutectic Al-7.7wt.%Ni alloy had the best fluidity. As cast microstructures as well as quenched microstructures during solidification and sample cooling curves were compared to investigate microstructure evolution in the Al-Ni system.