Jayesh B. Patel

Melt Conditioned Direct Chill Casting (MC-DC) Process for Production of High Quality Aluminium Alloy Billets

A novel direct chill (DC) casting process, melt conditioned direct chill (MC-DC) casting process, has been developed for production of high quality aluminium alloy billets. In the MC-DC casting process, a high shear device is submerged in the sump of the DC mould to provide intensive melt shearing, which in turn, disperses potential nucleating particles, creates a macroscopic melt flow to uniformly distribute the dispersed particles, and maintains a uniform temperature and chemical composition throughout the melt in the sump. Experimental results have demonstrated that, the MC-DC casting process can produce aluminium alloy billets with significantly refined microstructure and reduced cast defects. In this paper, we give an overview of the MC-DC casting process and report on results obtained from an industrial scale trial.

Grain refinement of deoxidized copper

This study reports the current status of grain refinement of copper accompanied in particular by a critical appraisal of grain refinement of phosphorus-deoxidized, high residual P (DHP) copper microalloyed with 150 ppm Ag. Some deviations exist in terms of the growth restriction factor (Q) framework, on the basis of empirical evidence reported in the literature for grain size measurements of copper with individual additions of 0.05, 0.1, and 0.5 wt pct of Mo, In, Sn, Bi, Sb, Pb, and Se, cast under a protective atmosphere of pure Ar and water quenching. The columnar-to-equiaxed transition (CET) has been observed in copper, with an individual addition of 0.4B and with combined additions of 0.4Zr-0.04P and 0.4Zr-0.04P-0.015Ag and, in a previous study, with combined additions of 0.1Ag-0.069P (in wt pct). CETs in these B- and Zr-treated casts have been ascribed to changes in the morphology and chemistry of particles, concurrently in association with free solute type and availability. No further grain-refining action was observed due to microalloying additions of B, Mg, Ca, Zr, Ti, Mn, In, Fe, and Zn (~0.1 wt pct) with respect to DHP-Cu microalloyed with Ag, and therefore are no longer relevant for the casting conditions studied. The critical microalloying element for grain size control in deoxidized copper and in particular DHP-Cu is Ag.

Liquid Metal Engineering by Application of Intensive Melt Shearing

In all casting processes, liquid metal treatment is an essential step in order to produce high quality cast products. A new liquid metal treatment technology has been developed which comprises of a rotor/stator set-up that delivers high shear rate to the liquid melt. It generates macro-flow in a volume of melt for distributive mixing and intensive shearing for dispersive mixing. The high shear device exhibits significantly enhanced kinetics for phase transformations, uniform dispersion, distribution and size reduction of solid particles and gas bubbles, improved homogenisation of chemical composition and temperature fields and also forced wetting of usually difficult-to-wet solid particles in the liquid metal. Hence, it can benefit various casting processes to produce high quality cast products with refined microstructure and enhanced mechanical properties. Here, we report an overview on the application of the new high shear technology to the processing of light metal alloys.

Grain refinement of DHP copper by elemental additions

Abstract The effects of additions of P and Ag, as well as the de-embrittling elements of copper—B, Mg, Ca, Ti and Zr—in concentrations of 0.085–0.5 wt-% to give some variations in contents within and outside of the DHP specification limits on grain size structure have been investigated under TP-1 casting conditions. Columnar to equiaxed transition has been observed with combined additions of 0.1%Ag–0.069%P; 0.4%Zr–0.039%P and with an addition of 0.5%B and, to a lesser extent, with an addition of 0.1%P and with combined additions of 0.4%Ag–0.030%P and 0.085%Ti–0.039%P. In contrast, 0.085% additions of Mg, Ca and Zr to DHP-Cu as well as 0.4%Ti to Cu failed to achieve grain refinement. Excessive coarsening of equiaxed grains has been observed with additions of 0.085–0.17%B, 0.4%Mg, 0.4%Ca and 0.5%P. Those results suggest making the maximum additions of P of 400 ppm and of Ag of 150 ppm to DHP-Cu for grain size control.

Grain Refinement of Phosphorus Deoxidised Copper

DHP-Cu has been modified with small additions of nanosized MgO particles, with and without P and B additions; and Mg, B, Ti and Al additions to investigate their effect on the grain structure under TP1 casting condition. In comparison to a reference DHP-Cu cast sample which exhibited mainly coarse columnar grains, a coarse equiaxed grain structure has been achieved with a single addition of nanosized MgO particles to a residual content of 34 ppm Mg. Whereas no grain refinement has been observed with nanosized MgO particles and P and B additions to a residual content of 109 ppm and 0.15% (nominal), respectively, and with a single addition of Mg to a residual content of 16 ppm. The combined additions of B and Ti, and B and Al to a nominal residual content slightly beyond the DHP-Cu specification have produced excessive coarsening of grains. Keywords: nanosized MgO particles; grain refinement; DHP-Cu

Melt Conditioning of Light Metals by Application of High Shear for Improved Microstructure and Defect Control

Casting is the first step toward the production of majority of metal products whether the final processing step is casting or other thermomechanical processes such as extrusion or forging. The high shear melt conditioning provides an easily adopted pathway to producing castings with a more uniform fine-grained microstructure along with a more uniform distribution of the chemical composition leading to fewer defects as a result of reduced shrinkage porosities and the presence of large oxide films through the microstructure. The effectiveness of high shear melt conditioning in improving the microstructure of processes used in industry illustrates the versatility of the high shear melt conditioning technology. The application of high shear process to direct chill and twin roll casting process is demonstrated with examples from magnesium melts.

Grain refinement of DHP copper by particle inoculation

Abstract The viability of grain refining phosphorus deoxidised, high residual phosphorus Cu (DHP-Cu) by particle inoculation through the formation of in situ Zr, Ti, Nb, La, Ce, Gd and Nd oxide particles, additions of WC and NbB2 particles as well as additions of Ti+B, Zr+B, Al+B and Ca+B with the purpose of forming in situ boride particles have been investigated under TP-1 casting conditions. Nominal additions of P in the range of 300–690 wt ppm and of Ag of 150 wt ppm have also been explored. In comparison, it appears that it is more difficult to grain refine DHP-Cu by particle inoculation than it is by the combined addition of P+Ag solute elements to a residual content of 396 ppm P and 143 ppm Ag (and having very low contents of Ti, Zr, Al, Ca and B microalloying elements) for the conditions studied.

Computational prediction of the refinement of oxide agglomerates in a physical conditioning process for molten aluminium alloy

This research is financially supported by the EC FP7 project “High Shear Processing of Recycled Aluminium Scrap for Manufacturing High Performance Aluminium Alloys” (Grant No. 603577).

Controlling the formation of iron-bearing intermetallics in wrought al alloys by melt conditioned dc (MC-Dc) casting technology

With the increasing use of recycled aluminium alloys from the end-of-life products more and more iron is accumulated into the compositions of alloys. Sometimes, recycling causes the iron levels to increase beyond the set target levels for down-stream processing. The only way to deal with this impurity currently in industry is to increase the primary aluminium added to the furnace to dilute the melt and re-add all other elements or cast it for re-melting or extrude it for products that is not surface finish critical or required higher corrosion resistance. Formation of small well dispersed spherical a- or small b- Fe-bearing intermetallics, which can be homogenised for shorter times and has no negative effect on downstream processing, would be promising even if the iron levels are above the targeted compositional limits. In the present paper, fine and dispersed Fe-bearing intermetallics have been achieved by Melt Conditioned DC (MC-DC) casting technology, instead of coarser Fe-bearing intermetallics forming network like morphology in the DC castings with grain refiner additions (DC-GR). This suggests feasibility of an increased tolerance of iron levels by melt conditioned DC casting technology.

Microstructure Evolution and Mechanical Properties of Thin Strip Twin Roll Cast (TRC) Mg Sheet

TRC Mg alloys are hot rolled to further reduce the thickness of the TRC strip which results in a sheet material with a relatively strong basal texture which produces anisotropic tensile properties based on the test direction. The low force TRC concept developed at BCAST provides a pathway to produce thin strip that does not require further hot rolling to achieve the final desired thickness. The as TRC and homogenised AZ31 show a refined grain and very little centre line. The as TRC AZ31 has a tensile yield strength of 220 MPa along the casting direction (CD) and 190 MPa perpendicular to CD showing a very small yield anisotropy.