Revisiting the Al-Si phase diagram upon a broad range of cooling rates

Guest Speaker： Senior Lecturer Dong Qiu,RMIT University，Australian

 Inviter: Assoc.Prof. Yangxin Li

Date&Time: Monday, 1. July. 10:00-11:30

Venue: Meeting room 216，Building B of SMSE

 Biography:

Dr Qiu was awarded a Ph.D degree majored in materials science and engineering from Tsinghua University in 2005. He had been working as a Postdoctoral Research Fellow, and then Australian Research Fellow at the University of Queensland from 2005 to 2014. Dr Qiu joined RMIT University in 2015 as a Vice Chancellor’s Senior Research Fellow and was promoted to Senior Lecturer in 2019. In the last 20 years, his research has spanned a range of areas, such as grain refinement of cast metals, crystallography in solid-solid phase transformations and surface modification of biomedical implants. His contribution to the research community is witnessed by 110 peer-reviewed journal papers, with 1 out of those published in Nature, 3 published in Nature Communications, 18 published in Acta Materialia, the leading journal in the field of physical metallurgy worldwide. His publications have been cited by more than 5800 times and his H-index is 39 in Scopus. He has also succeeded in obtaining fund of 5 Australian Research Council (ARC) Discovery Projects and 1 ARC Linkage Project. Dr Qiu is currently appointed as a Key Reader of ‘Metallurgical and Materials Transaction A’ and an ARC Assessor. His current research interest includes microstructure manipulation of additively manufactured (AM) metal components and new alloy development through AM

 Abstract:

The emerging metal additive manufacturing (AM) usually features a much higher cooling rate during solidification (104~106 K/s) than that in conventional sand casting. The high cooling rate does not only refine the microstructure but can also induce a substantial change on the phase constituents and their fraction, which is far from what is derived from equilibrium phase diagram. Therefore, it poses a great challenge to predict the actual phase constituents and their fraction in the as-fabricated AM components. In this study, a near eutectic Al-10Si model alloy was fabricated using high-pressure die casting (HPDC) and powder bed fusion-laser beam (PBF-LB) processes. After comprehensive microstructure characterization, considerable differences were identified in Al-Si eutectic volume fractions, eutectic Si composition, eutectic undercooling, and the solubility of Si in the Al matrix with the increase of cooling rate. A series of empirical relationships were developed relating to cooling rate and microstructure. Based on the Scheil-Gulliver analysis, a ‘kinetic phase diagram’ is proposed for the Al-Si system to precisely reflect the cooling rate effect on the as-fabricated samples' phase constituents and their constituents. This is an original study that, for the first time, systematically investigated the effect of cooling rate in a wide range (10-3 to 106 K/s) on the microstructure formation of near eutectic Al-Si alloys. The developed empirical relationships will primarily benefit but not be limited to microstructure modelling, process design, and alloy development when a high cooling rate is accompanied.