.18 K White Gold Alloy Master Alloy And Its Refined Performance

Jewelry business, especially gold alloys used in jewelry, has developed greatly in recent years. But there are still great deficiency compared to international actuality because of historical reasons. As a result, master alloys for Gold alloys, which are generally Cu-Ni-Ag(Zn) complex alloys, are mostly imported from other countries. As other alloys, grain refinement can greatly improve properties of gold alloy. Some articles have mentioned that rare earth elements have a grain refinement effect on gold alloys, but a detailed introduce on that is not available.Various smelting processing were studied during the preparation of master alloys for gold alloys. Master alloys were prepared with various RE additions (La and Ce, percentage composition varies from 0.2%-2.0%), and the effect of RE additions on master alloys was studied. White gold alloys, which were prepared from master alloys, were investigated by metallographic examination, X-ray diffraction (XRD), scanning electron microscope (SEM), microhardness test. The results obtained were summarized as follows:(1) Various antioxidation processing, including different covering flux, with or without gas protection, various way in which RE are added ,are studied. Under a finally chosen processing, burn out rate of Zinc is about 5%, absorbance rate of RE is about 60%.(2) By control of pouring temperature, height, speed and the shape, size of stainless steel sieve, homogeneous particles of master alloys, circular or elliptic, size in 1-3mm, are prepared with smooth surface.(3) Grain size of master alloys decrease first and increase later with increasing RE addition. Metallographic examination shows that precipitated phase particles, which are RE compounds according to the result of energy spectrum, exist homogeneously between dendrites.(4) XRD analysis of gold alloy samples shows that compared to the gold alloys without RE addition, alloys with La addition have two new intermetallic compound phase: Cu₅La å'Œ Au₅₁La₁₄, alloys with Ce addition have a new RE Oxysulfide phase:Ce2O2S.(5) Metallographic examination and SEM observation of gold alloys shows: grain size of gold alloys, primary dendritic arm spacing and secondary dendritic arm spacing all decrease first and increase later. Precipitated phase particles exist homogeneously between dendrites, and the number of precipitated phase particles increases with the increasing number of RE addition. When percentage composition of RE addition is above 0.2%, precipitated phase particles start to aggregate.(6) The microhardness of gold alloys increase first then decrease and increase again with the increasing RE addition. Associated with XRD, metallographic examination and SEM observation result, the harden mechanics can attribute to solution strengthening and precipitated phase strengthening.