Effects of cooling rates on microstructure and microhardness of lead-free Sn-3.5%Ag solders  

作　　者：沈骏 刘永长 韩雅静 高后秀 韦晨 杨渝钦 

机构地区：[1]College of Materials Science and Engineering, Tianjin University, Tianjin 300072, China

出　　处：《中国有色金属学会会刊：英文版》2006年第1期59-64,共6页Transactions of Nonferrous Metals Society of China

基　　金：Project(50401033) supported by the National Natural Science Foundation of China; Project(200335) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of China; Project(033608811) supported by the Natural Science Foundation of Tianjin City, China; Project supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry

摘　　要：The microstructure and microhardness of Sn-3.5%Ag solders were explored in the cooling rate ranging from 0.08 to 104 K/s. Under rapid cooling condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium eutectic point, and the actual metastable eutectic point shifts to the higher Ag concentration. Hence, the higher the applied cooling rate is, the more the volume fraction of primary β-Sn crystal forms. At the same time, the separation of primary β-Sn crystal favors restraining the formation of bulk Ag3Sn intermetallic compounds (IMCs) in solder due to the mismatch crystalline orientation relationship, those Ag3Sn phase separating through the eutectic reaction could hardly cling to the primary β-Sn crystal and grow up. Additionally, the Vickers hardness test shows that fine β-Sn and spherical Ag3Sn phase in the rapidly solidified alloy strongly improves the microhardness of the Sn-3.5%Ag solder.The microstructure and microhardness of Sn-3.5%Ag solders were explored in the cooling rate ranging from 0.08 to 10^4 K/s. Under rapid cooling condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium eutectic point, and the actual metastable eutectic point shifts to the higher Ag concentration. Hence, the higher the applied cooling rate is, the more the volume fraction of primary β-Sn crystal forms. At the same time, the separation of primary β-Sn crystal favors restraining the formation of bulk Ag3Sn intermetallic compounds （IMCs） in solder due to the mismatch crystalline orientation relationship, those Ag3Sn phase separating through the eutectic reaction could hardly cling to the primary β-Sn crystal and grow up. Additionally, the Vickers hardness test shows that free β-Sn and spherical Ag3Sn phase in the rapidly solidified alloy strongly improves the microhardness of the Sn-3.5%Ag solder.

关 键 词：显微硬度 无铅焊料 Sn-3.5%Ag合金 共晶转变 金属间化合物 冷却速率 显微结构 

分 类 号：TG42[金属学及工艺—焊接]