Trace Elements Y, Si 925 Silver Alloy Corrosion Resistance And Corrosion Mechanism

Silver alloys show wide development prospect in the jewelry industry due to their low-price and high gloss. However,one major impediment to the development of silver alloys is their poor sulfuration resistance. Tarnishing of silver and its alloys in certain environments is a persistent problem. Until now, not many experimental researches are available on the sulfuration behavior of silver alloys. This work, were made evaluation and comparision of the effects of chemical composition in silver alloys,and different types of silver alloyed with various chemical compositions (copper, aluminium,silicon,yttrium) were developed. The objective of this work was to develop a kind of antitarnished silver alloy and ascertain the influence of silicon and yttrium on the corrosion mechanism and resistance to aging and softening of silver- copper alloys.The effect of composition on the Sulfuration and oxidation products of silver alloys were investigated, by means of OM, XRD, SEM , EDS. On the basis of experimental research, the theoretical analysis was made on the corrosion behavior of silver alloys. The following results were obtained:1.The silver alloys prepared showed good performances:cast hardness exceeded HV110 and rolled hardness exceeded HV150, after age hardening at 240°C .Excellent mechanical properties were maintained after corrosion in harsh environment.2.The additition of trace element Si led to (0.04%-0.08%)an increase in alloy fluidity, and improvements ingot surface quality, anti-tarnish capability, and mechanical properties. Optimal modification effect could be obtained at 0.04%-0.06% silicon content.3.Microstructure refined significantly and simultaneously improves the mechanical properties of silver alloy, thanks to minor additition base metals element yttrium (0.03%-0.07%) ,the level of the gas and detrimental elements content of the silver alloy ingots. Morever, minor yttrium had excellent discoloration-resistance and corrosion resistance. Also, the age softening resistance of silver alloy was improved. Optimal modification effect and the highest anti-tarnished capacity could be obtained at 0.03% RE content.4.Based on the research corrosion layers we found that: the products of corrosion formed three layers: oxide layer (outer layer), sulfide layer (middle layer), and diffusion layer (inner layer). The oxide layer was mainly composed of Cu₂O, instead of AgO and Ag₂O, while the oxide layer is mainly composed of Cu₂S, instead of Ag₂S.