Cast Shop Technology: Recycling and Sustainability Joint Session: Cast Shop/Recycling Joint Session
Sponsored by: TMS Extraction and Processing Division, TMS Light Metals Division, REWAS Organizing Committee, TMS: Aluminum Committee, TMS: Recycling and Environmental Technologies Committee
Program Organizers: David Gildemeister, Arconic Technology Center; Anne Kvithyld, SINTEF; Elsa Olivetti, Massachusetts Institute of Technology
Tuesday 2:00 PM
February 28, 2017
Location: San Diego Convention Ctr
Session Chair: Elsa Olivetti, MIT
Tramp Element Accumulation and Its Effects on Secondary Phase Particles: Robert Wagstaff1; Samuel Wagstaff2; Antoine Allanore2; 1Novelis Inc.; 2Massachusetts Institute of Technology
Increased demand for wrought aluminum products has put pressure on suppliers to increase the amount of recycled material used in the production stream. While this has financial and ecological benefits, even single-source scrap streams never exhibit the composition profile of the original product. This accumulation of so-called “tramp” elements such as iron, chromium, and vanadium can have an impact on the secondary phase inter-metallic particles formed during Direct-Chill (DC) casting. In order to better understand the influence of increased concentrations of certain tramp elements, an AA3104 ingot has been cast with an increased level of iron compared to the standard. The secondary phase particles have been analyzed as a function of position using a deep-etch technique and compared to grain size and macrosegregation profiles.
Dross Formation Mechanisms of Thermally Pre-treated Used Beverage Can Scrap Bales with Different Density: Jan Steglich1; Regina Dittrich2; Georg Rombach3; Marcel Rosefort1; Bernd Friedrich2; Anne Pichat4; 1TRIMET Aluminium SE; 2RWTH Aachen University; 3Hydro Aluminium Rolled Products GmbH; 4Constellium Technology Center
Used beverage can scrap (UBC) bales can be remelted in state of the art multi-chamber furnaces. Following the recycling of baled UBC scrap in multi-chamber furnaces, a laboratory scale process route was developed for thermal pre-treatment and submerged melting of the scrap. In the present work, UBC scrap types with different density and level of contamination are compared. The scrap types were thermally pre-treated in different atmospheres up to 550 °C and subsequently melted by submerging in a salt-free laboratory process. Melting was performed in pure aluminium at 750 °C under protective argon atmosphere to exclude the influence of thermolysis gases and air. The impact of remaining organic contamination and oxidation products after thermal pre-treatment on dross formation were described. Results of SEM EDX analysis, as well as thermochemical calculations, were used to explain reactions between solid scrap and the liquid aluminium melt to improve recycling efficiency.
Influence of Coating and De-coating on the Coalescence of Aluminium Drops in Salt: Stefano Capuzzi1; Anne Kvithyld2; Giulio Timelli1; Arne Nordmark2; Thorvald Abel Engh3; 1Univerity of Padua; 2SINTEF; 3NTNU
In a rotary furnace for aluminium recycling and dross treatment, a salt flux is added which protects against oxidation and captures non-metallic impurities. Furthermore, the salt has to promote the coalescence of the metal drops in the dross. This work investigates the coalescence of molten aluminium for different types of scrap. Hundred discs were stamped from aluminium alloy sheets with and without coating. They were melted, covered in NaCl-KCl-Na3AlF6 molten salt, in an induction furnace at 790°C. The solidified aluminum droplets were extracted by leaching the salt with water. The fraction of coalesced drops and the average diameter were determined to evaluate the coalescence efficiency. The effect of various de-coating temperatures was studied. The results show that the coalescence is negatively affected by coating. Long holding times has no effect. Complete coalescence off all discs are achieved with uncoated scrap. The drops coalesce if the temperature of the combustion reaction for the coating is attained.
The Scale-up of High Shear Processing for the Purification of Recycled Molten Scrap Aluminium Alloy: Key Features of Fluid Flow: Mingming Tong1; Jayesh Patel2; Ian Stone2; Zhongyun Fan2; David Browne3; 1University College Dublin; NUI Galway; 2Brunel University London; 3University College Dublin
In order to remove impurities in scrap aluminum alloys, hence increasing their value, a laboratory-scale high shear processing (HSP) unit for mixing the molten alloy was developed, which makes it possible to remove iron-based contaminants using physical conditioning, at relatively low cost. In order to make this technology applicable in the industrial environment, we are now investigating the scale-up of HSP by using computer simulation. The computational research quantitatively predicts a variety of key features of fluid flow, which determine the feasibility of the scale-up. These include the mass flow rate through the mixing head, the effective agitation of the melt in the bulk crucible, and the shear rate that can be achieved. Based on the configuration of HSP that we review in this paper, we predict that it is feasible to achieve a factor of four scale-up in the volume of liquid alloy treated.
3:20 PM Break
Centrifugal Casting of Al-Si Scrap: Aya Abdelrahman1; Shimaa El-Hadad2; Iman El Mahallawi3; 1British University in Egypt; 2Centre for Metallurgical Research and Development; 3Cairo University
Recycling is a sustainability aspect that ensures green environment as well as energy and cost reduction. Sustainability and reduced energy consumption requirements demand that AlSi alloys are recycled by remelting. Al-Si cast alloys industries are increasing, leading to more consumption of these alloys that in turn leads to more scrap. Unfortunately, when cast Al-Si alloys are recycled, extraneous microstructures combined with reduction in the mechanical properties occur. In this research, the microstructure of recycled Al-Si alloys produced by centrifugal casting using different parameters was studied. The changed parameters are the centrifugal rpm and scrap material mix. The microstructure of the recycled cast Al-Si alloys was observed to improve by centrifugal casting, resulting a graded microstructure from inner to outer surface of the casting. The centrifugal separation is shown to be a promising method for controlling the Fe-rich enormous structures and the porosity present in the recycled Al-Si alloys.
Improved Recyclability of Cast Al-alloys by Engineering β-Al9Fe2Si2 Phase: C. B. Basak1; N. Hari Babu2; 1BCAST, Brunel University London ; 2BCAST, Brunel University London
Castability and tensile properties of recycled cast Al-Si alloys are affected by the presence of high iron content. The present study demonstrates a promising scope of better recyclability by engineering the intermetallic β-phase that present in cast Al-6wt% Si model alloy systems with as high as 2wt% Fe. Thermodynamic interplay between Si and Fe concentration on the formation of the β-phase and the solidification behaviour of this hypoeutectic Al-Si alloy has been explored. It has been demonstrated that suitable heat treatment alters the morphology of the β-phase and simultaneous addition of Cu improves the strength. Based on the experimental evidences, the mechanism behind the solid-state morphological changes of beta phase has been proposed. Experimental results and thermodynamic calculations suggest that Cu content of more than 2wt% marginally increases the yield of beta phase; however, at 4wt% Cu the solid solution strengthening improve the strength of solutionized alloy.