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

Characterisation of fresh surface films formed on molten Mg-Nd alloy protected by different atmospheres

This study examines the early stages of surface oxidation of liquid Mg-3 wt%Nd under UPH argon, dry air, and air mixed with protective fluorine-bearing gases. Each of the gases were introduced as bubbles into solidifying castings. The chemistry and structure of the protective film inside the trapped bubbles were characterized by SEM and EDX analyses. Results show that due to Nd added to Mg alloy under dry air, a dense and wrinkled surface film that contains MgO and NdO are formed. Under fluorine-bearing gas mixtures, a dense and coherent surface film was found to be a mixed fluoride and oxide. For SF, the film thickness was 50-100 nm thick while for HFC-R134a it was 35-45 nm. Needle shaped phases distributed in the Mg matrix and flake-like phases segregated on the inner bubble surface in proximity to the interdendritic regions of the alloy were both identified as Nd rich compounds. These were present under all gas conditions. The results obtained lead to a conclusion that HFC-R134a is capable of providing the most effective melt protection. The integrity and protective capability of the early surface film formation on the liquid Mg-Nd alloy was found to be significantly improved compared to pure Mg under identical gas conditions due to formation of a dense and compact MgO/NdO layer, regardless of whether fluorine species were also present

Study on the early surface films formed on Mg-Y molten alloy in different atmospheres

In the present study, the non-isothermal early stages of surface oxidation of liquid Mg-1%Y alloy during casting were studied under UPH argon, dry air, and air mixed with protective fluorine-bearing gases. The chemistry and morphology of the surface films were characterized by SEM and EDX analyses. The results indicate a layer of smooth and tightly coherent oxidation film composed of MgO and YO formed on the molten Mg-Y alloy surface with 40-60 nm thickness under dry air. A dendritic/cellular microstructure is clearly visible with Y-rich second phases gathered in surface of the melt and precipitated along the grain/cell boundaries under all gas conditions. Under fluorine-bearing gas mixtures, the surface film was a mixed oxide and fluoride and more even; a flat and folded morphology can be seen under SF with oxide as dominated phase and under 1, 1, 1, 2-tetra-fluoroethane, a smooth and compact surface film uniformly covering the inner surface of the bubble with equal oxide and fluoride thickness, which results in a film without any major defects. MgF phase appears to be the key characteristic of a good protective film