Study On Strengthening Mechanism And Anti-discoloration Performance Of Aluminum On Stirling Silver

Pure silver with beautiful white luster and stable chemical properties,often used in the jewelry industry.However,Pure silver is too soft to meet the processing requirements.Compared with pure silver,Sterling Silver is widely used in jewelry alloys because of its high strength,hardness,excellent processing performance,and color gloss close to pure silver.However,Stirling Silver also has problems such as insufficient hardness,poor oxidation resistance,and poor color resistance.At present,a series of commercial anti-tarnish Stirling silver has been developed by alloying at home and abroad,but it still cannot meet people’s actual needs.Therefore,this subject adds the alloying element Al to Stirling Silver to study the effect of Al on the strengthening mechanism of Stirling Silver and the resistance to discoloration,providing some theoretical support for the development of Stirling silver with high hardness and excellent resistance to discoloration.This subject discusses the strengthening mechanism of Stirling Silver by analyzing the microstructure and mechanical properties of the Stirling silver as-cast alloy,the microstructure and hardness of the alloy during the heat treatment process;through the analysis of Stirling silver’s resistance to high-temperature oxidation discoloration,the verification of the oxidation resistance of the alloy to oxidation discoloration,the simulation of alloy sulfidation corrosion discoloration and salt spray corrosion discoloration,and the test of the alloy’s electrochemical corrosion resistance,to study the effect of aluminum on the discoloration resistance of Sterling Silver.The main research conclusions are as follows:1.The addition of aluminum obviously improves the mechanical properties of Stirling Silver.When 2 wt.%Al is added,the AC₂ alloy has the highest as-cast hardness.After annealing,the AC₂alloy has better work hardening properties,and the tensile properties yield strength and tensile strength increase,but the elongation slightly decreases;after 800 ℃/5 h solution treatment and 350 ℃/80 min aging treatment,the hardness of AC₂ alloy is the highest,reaching 218.57 HV_0.2.2.The strengthening method of aluminum to Stirling silver is compound particle strengthening and aging precipitation strengthening.In the as-cast alloy,aluminum segregates in the dendrite gap to form a compound that produces particle strengthening relative to the alloy;after the aging treatment,the needle-shaped precipitation of copper and aluminum formed during the aging of the alloy produces aging strengthening relative to the alloy.3.The addition of aluminum improves Sterling Silver’s resistance to high temperature oxidation and discoloration.The thermal oxidation experiment further confirmed the improvement of aluminum’s resistance to discoloration during the Stirling Silver oxidation process,and thermal oxidation will form a composite oxide film composed of aluminum oxide and copper oxide on the alloy surface.4.In sterling silver sulfide corrosion simulation and salt spray corrosion simulation,the addition of aluminum slowed down the corrosion discoloration of the alloy.With the increase of aluminum addition,the discoloration resistance of sterling silver to sulfide corrosion was enhanced,but the discoloration resistance to salt spray corrosion was not significantly enhanced.After the heat oxidation of sterling silver with aluminum,the existence of copper oxide in the oxide film will lead to the formation of copper sulfide easily and weaken the anti sulfur discoloration ability of the alloy;moreover,copper oxide accelerates the formation of corrosion products in the salt spray process of the alloy,however,there is no significant difference between the corrosion discoloration of each alloy and that of the unoxidized alloy.5.Electrochemical data shows that the addition of aluminum has little effect on the overall corrosion rate of Stirling Silver,but due to the presence of compound particles,it will reduce the pitting potential of the alloy,reduce the resistance of the alloy to pitting corrosion,and the surface of the alloy is easy local corrosion occurs.After 200 ℃/60 min thermal oxidation treatment,it can increase the pitting potential of Stirling Silver to a certain extent and improve the pitting corrosion resistance of the alloy.6.Combining the changes of Stirling silver’s mechanics and its resistance to discoloration and corrosion,the optimal addition amount of aluminum is 2 wt.%,and the optimal thermal oxidation process is 200 ℃/60 min.