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TRODUCTION

IN

early work, grain refinements of copper[1,2] and low alloy copper (which here refers to a maximum of 2 pct[1] and 2.6 pct,[2]) were investigated in air. In the 1990s, grain refinement of copper was investigated under a protective atmosphere of pure Ar (99.997 pct), (enclosed chamber filled with Ar in a vacuum induction furnace, following vacuum purging).[3–6] Despite this demonstrable grain refinement of copper, exploitation of the beneficial solute additions was not on the whole applied to DHP-Cu with a view to becoming mainstream industrial practice. DHP-Cu is commercially pure copper (99.9 pct min. inclusive of 0.015 pct max. Ag), which has been deoxidized with P, leaving relatively high residual P in the range of 0.015-0.04 pct (all percentage compositions here are given in wt pct and ppm in wt ppm). DHP-Cu is one of the most common grades of copper and is a versatile material being used for engineering applications (nonelectric) such as sheet, plate, pipe, tube, and fittings.[7] An as-cast fine-grain size structure in thin-walled DHP-Cu tube, for example, is important to reduce the susceptibility of crack propagation all the way across the tube wall thickness during the subsequent drawing and bending operations, ultimately resulting in rejection of the product.[8] It is also important to significantly improve the mechanical properties of both cast and

MARI´A JOSE´ BALART and FENG GAO, Research Fellows, JAYESH B. PATEL, Senior Research Fellow, and ZHONGYUN FAN, Professor, Director of BCAST, are with the BCAST, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK. Contact e-mails: [email protected], [email protected] Manuscript submitted September 24, 2015. Article published online August 1, 2016 4988—VOLUME 47A, OCTOBER 2016

wrought products.[9,10] Hence, control of grain size in DHP-Cu is needed for an optimal combination of high component integrity, reduced component-processing costs, improved energy efficiency, and therefore reduced downstream CO2 emissions, increasing the importance of economically attractive recyclable copper at the end of its life to avoid degrading quality. DHP-Cu (99.9 pct min.) is obtained from copper cathode (99.9 pct min.-99.99 pct). During the electrolytic-refining process, copper cathodes are produced, whereby impurities are removed and valuables are recovered by separation. Ag, Au, and Pt are precious metals and are nobler than copper. They will be found as metals in the anode slime. More detail is given later, but a focal point has been to identify inoculant particles and solutes, which could be generated from commercially available copper-based master alloys, for grain structure control of copper and in particular DHP-Cu during solidification. The range includes master alloys such as copper-boron, copper-phosphorus, copper-zirconium, and copper-silver. Alternatively, by-product metals (Zn, In, Ag, etc) produced during the refining of copper[11] can potentially be used directly for the same purpose. In this paper, taking as a starting point a brief overview of the work