Ultrasonic Fractional Purification of Recycled Al Alloys

Lead Research Organisation: Brunel University
Department Name: Inst of Materials & Manufacturing: BCAST

Abstract

Abstract
This PhD project will develop fundamental and applied basis for fractional solidification technology of recycled aluminium alloys. The novelty of the project is in combination of thermochemistry of recycled alloys, ultrasonic processing of melt and fractional solidification for achieving higher purity of aluminium extracted from recycled stock.

Keywords
Solidification, aluminium, partitioning, ultrasound, recycling

Project Scope and Research Objectives Defined
Recycled Al alloys are typically contaminated with harmful impurities of Fe, Mn and other elements that form eutectic systems with Al. Currently the re-use of such alloys involves their dilution with primary alloys or aluminium (expensive and with larger carbon footprint) or by additions that modify the shape of the intermetallics (maybe expensive and harmful for other properties, e.g. corrosion).

There are some earlier works where interrupted (fractional) solidification was suggested as a technologically viable way of purification of the melt from soluble impurities. In eutectic systems, e.g. Al-Fe, Al-Mn, Al-Cu, Al-Mg, Al-Si, hypoeutectic alloys show large partitioning of solute elements between liquid and solid phases, with these (impurity) elements accumulating in the liquid phase while the solid phase (Al) remaining almost pure especially in the early stages of solidification.

In the fractional solidification method, a water- or air-cooled substrate is put into a contaminated melt and solidification of relatively pure Al starts on it, while the rejected solute is accumulated in the rest of the melt. At a certain moment the substrate with the purified Al is extracted from the residual melt. The remaining melt can be recycled as master alloys or subjected to repeated fractional solidification.

Ultrasonic processing of melts is known to induce special conditions such as heating, cavitation and streaming that may have potential benefits for fractional solidification, accelerating the diffusion and transport of the melt from the solidification (reaction) zone.

There are three main challenges in the proposed project
a better understanding and the related ability to establish control of fractional solidification using dedicated experiments, thermodynamic modelling and heat/mass transfer simulations.
understanding the mechanisms of ultrasonic treatment in the fractional solidification through smaller scale experiments.
design and test a prototype system and demonstrate the feasibility of the approach in application to the scrap of different origin and composition.

The results obtained will be of considerable scientific and applied value and publishable in leading scientific journals and conferences (following the agreed approval procedure).

The research objectives are:
1. Study the fundamentals of fractional solidification based on thermodynamic modelling (Thermocalc) and experimental work. - knowledge transfer.
2. Establish the relation between the process parameters (melt and substrate temperatures, solidification and cooling rates, ultrasonic parameters, composition of the initial and target alloys) and the degree of purification. - knowledge transfer.
3. Design and built a lab-scale prototype to test the feasibility of the developed approach as applicable to the recycled alloys of different origin (automotive, construction, aircraft scrap). - knowledge transfer.
4. Educate a young scientist. Milestone - PhD.

Expected key project outcomes defined, i.e. New technology or PhD or Creation of new Standards or creation of new processes, etc.
This project will create new knowledge for JLR in the form a PhD thesis in the subject of aluminium recycling which will help shape the sustainable future for JLR products.
This project will provide a working lab-scale prototype for further technological development along with a number of reports and scientific papers.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/P510439/1 01/10/2016 30/09/2021
1815386 Studentship EP/P510439/1 01/11/2016 30/04/2021 Susanna Venditti
 
Description The research project is about the fractional solidification of aluminium alloys to recycle Al. Temperature is a key parameter, the alloy needs to be processed in isothermal conditions at a specific temperature calculated by Thermocalc. The purpose is to process the alloy in the semi solid state in order to squeeze the liquid out of the mush as much as possible to achieve a high purification level. The key to do it is to understand how the liquid migrates through the mush. We studied the liquid migration and behaviour with the help of Computed Tomography, SEM and EDX measurements and optical microscopy images. Moreover, through the use of a modelling calculation, we are able to confirm that no solid diffusion happens during the isothermal squeezing so that the purification is not affected.
Exploitation Route The outcomes both fundamental and technological may be taken by JLR and partners to the practical implementation stage, e.g. technology development or prototype building.
Sectors Aerospace, Defence and Marine,Construction,Energy,Manufacturing, including Industrial Biotechology,Transport

 
Description AMPC launch 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact i presented a poster about my research at the event organised for the launch of the AMPC facility in Bcast where I am enrolled as PhD student. It was a good occasion to share with my colleagues, and some external members of the Academia and the industrial environment, my research. I received interesting advice and I could also practice my skills in presentationa and public speaking.
Year(s) Of Engagement Activity 2018
 
Description International Conference on Aluminium Alloys 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Presenting a poster on the project during a poster session at the International Conference on Aluminium Alloys in Montreal, Canada
Year(s) Of Engagement Activity 2018
 
Description TMS2020 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Oral presentation on the outcomes of this project at an Annual Meeting of TMS (The Minerals, Metals and Materials Society of America): symposium on recycling
Year(s) Of Engagement Activity 2020