| High temperature lead-free solder plays a key role in mechanical connection,electric and heat conduction in the packaging of electronic products.Lead in traditional lead-tin solders has a serious impact on human health and the natural environment,thus,Europe and China have issued the Ro HS Directive and“Pollution Control Measures for Electronic Information Products”,which clearly restricts the use of lead-containing solders.Therefore,lead-free solder has become a research hotspot in the field of electronics.Bi-Ag alloy has a suitable eutectic temperature（262.5℃）,hardness and95Pb5Sn（wt.%）solder alloy is similar,the price is suitable,However,how to optimize the properties of alloy through alloying is the key to the practicability of lead-free solder.In this paper,the effects of Ag/Zn content and alloying elements（Sb,Ce,Al,Cu）on the melting properties,microstructure,resistivity,hardness,oxidation resistance,wettability and corrosion resistance of Bi-Ag-Zn alloy system in 3.5%Na Cl solution were systematically studied.Main research contents and conclusions:（1）The influence of Ag/Zn content and the fourth element alloying elements（Sb,Ce,Al,Cu）on the melting performance of Bi-Ag-Zn alloy solder were studied.It was found that the solder melting range increased with the increase of Zn element,and the presence of Ag5Zn8 phase in Bi2Ag2Zn and Bi2Ag3Zn solder greatly reduced the temperature of solid phase line.which led to the expansion of alloy melting distance;With the increase of Ag element,the melting range of solder decreased,and the melting range of Bi5Ag2Zn solder was 7.5℃,which showed excellent melting performance.The addition of Sb or Al was increased the melting range of the alloy and reduced its melting property,while the addition of Ce had little effect on the melting property of the solder.When the Cu content reached 4%,the melting range of the alloy increased obviously,therefore,the Cu content should be controlled below 4%.（2）The effects of Ag/Zn content and the fourth component alloying elements（Sb,Ce,Al,Cu）on the conductivity and hardness of Bi-Ag-Zn alloy solder were studied.The results showed that the resistivity of the alloy was decreased first and then increased with the increase of Ag and Zn contents,and the conductivity of Bi5Ag2Zn solder was the best,which was about 1.04μΩm.The addition of Sb or Ce was improved the resistivity of the solder,with the increase of Al content,the resistivity of the alloy was increased first and then decreased,Besides adding Cu can improve the conductivity of the alloy.With the increase of Ag and Zn elements,Ag-Zn hard phase was formed in the alloy,resulting in the increase of the hardness of the alloy.The addition of Sb was generated hard Bi-Sb phase in the alloy and then improved its hardness,while the addition of a small amount of Ce and Al had little effect on the hardness of the solder.The addition of Cu can increase the hardness of solder.（3）The effects of Ag/Zn content and the fourth component alloying elements（Sb,Ce,Al,Cu）on the oxidation resistance and wettability of Bi-Ag-Zn alloy solder were studied.The results showed that the addition of Ag,Sb and Al contributed to the improvement of the oxidation resistance of the alloy,while the addition of Ce and Zn decreased the oxidation resistance of the alloy.The wettability Angle of the molten Bi-Ag-Zn solder on the pure copper surface was between 30°and 45°,in which the wettability Angle of Bi5Ag2Zn0.3Al solder was 36°and that of（Bi5Ag2Zn5Sb）2Cu solder was 33°.（4）The effects of Ag/Zn content and the fourth component alloying elements（Sb,Ce,Al,Cu）on the electrochemical properties of Bi-Ag-Zn alloy solder in 3.5%Na Cl solution were studied.The results showed that increasing the content of Ag and Sb can improve the corrosion resistance of the alloy in 3.5%Na Cl solution,while increasing the content of Zn and Al reduced the corrosion resistance of the alloy.In the designed Bi-Ag-Zn-X（X=Cu,Ce）alloy,（Bi5Ag2Zn5Sb）4Cu alloy and Bi5Ag2Zn0.3Ce alloy showed excellent corrosion resistance. |
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