Selecting conditions of preparation of copper-based melts for spraying

Abstract

The chemical heterogeneity of copper and its alloys in respect of certain elements in relation to the thermal and time conditions of melting and the effect of the type of deoxidizing agent on the content of oxygen and nonmetallic inclusions were examined on rapidly cooled cylindrical specimens 4-6 mm in diameter produced by sucking the liquid metal into quartz tubes at specific periods in melting, followed by rapid cooling in water. Metal samples were taken from laboratory and industrial melts of copper and its alloys in induction furnaces with a capacity of 65-1000 kg using graphite crucibles. The charge was represented by M0 grade copper (cathodes, waste from elctrotechnical industry: pressings, conductors, powder blanks, etc.), grade TsO zinc (Tsl), grade SO (SI) lead, grade Ol (02) tin. Deoxidation was carried out with a 0.02-0.10% copper--phosphorus (MF-10) and copper-boron (2% boron) master alloy. To reduce the extent of gas absorption, all the melts were covered with a dried charcoal layer 60-120 mm thick. The deoxidizing agent was added after melting copper. This was followed by adding alloying elements, with tin added last. Samples of the melts to be used for further dispersion by water to produce nonspherical powders were taken at temperatures of 1180-1280 (copper), 1100-1220 (L80 brass), and I080-I150°C (BrOTsS bronze) in 20 deg intervals. The holding time at each temperature was 10-30 min. Sections were prepared from the cylindrical specimens. The degree of homogeneity of the distribution of the solute and alloying elements was analyzed in Superprobe-733 equipment, the oxygen content was estimated in a device manufactured by Balzers Company, the number of nonmetallic inclusions in Quantimet equipment, and the volume fraction of the inclusions was calculated in measuring 500 fields of view on each section. The results show that the degree of chemical heterogeneity of the copper melt greatly decreases after thermal treatment at 1250°C with holding for 20 min, and that of the melts of brass and bronze decreases after treatment at 1180 and I130°C and holding for 15 and 20 min, respectively. Figure 1 shows the concentration curves of the maximum and minimum values of microheterogeneities in respect of the solid and alloying elements for copper, brass, and bronze. As an example, Tables 1 and 2 give the average results of examination of the effect of the oxidizing agents (phosphorus and boron) on the content of oxygen and nonmetallic inclusions in OTsS 5-5-5 bronze. It can be seen that boron results in lower oxygen concentration than phosphorus. When the boron concentration is increased to 0.06% the amount of oxygen rapidly decreases. A further increase of the boron concentration is less effective and the fraction of spherical powder particles increases. This impairs the technological processes of the powder. Subsequent addition of zinc to the melt results in an additional reduction of the oxygen concentration. The content of the nonmetallic inclusions decreases on adding both deoxidizing agents, but in deoxidation with boron a subsequent addition of zinc to the melt is not accompanied by an increase of the volume fraction of the inclusions.