Study On Impression Creep Property And Microstructure Of Sn-Ag-Zn Lead-free Solder

Taking the most promising substitute of Sn-3.7Ag-0.9Zn solder as the research base, investigations were made to explore the rules of effect of trace elements In, Al and Ce-rich rare earth on microstructure and impression creep property of Sn-3.7Ag-0.9Zn alloys. In addition, microstructure and impression creep property of Sn-xAg-0.9Zn (x=0.3, 0.5, 2.0, 3.0) alloys were studied.The results indicate:(1) The microstructure of Sn-3.7Ag-0.9Zn composed withβ-Sn, Ag₃Sn and AgZn. After the Ce-rich rare earth added in the Sn-3.7Ag-0.9Zn lead-free solder, the microstructure of the alloys composed withβ-Sn, Ag₃Sn, AgZn and CeSn3. When Al elements added, the microstructure of the alloys composed withβ-Sn, Ag₃Sn, AgZn and Ag2Al. For the Sn-xAg-0.9Zn(x=0.3, 0.5, 2.0, 3.0) alloys, Ag₃Sn and AgZn intermetallic compounds are generated easier with the increase of the Ag contents. Afterβ-Sn phase separated, granular intermetallic compounds attached in its grain boundary exhalation and grow up. There is no effect with In added, the microstructure of alloys still composed withβ-Sn, Ag₃Sn, AgZn.(2) The study on Sn-3.7Ag-0.9Zn, Sn-3.7Ag-0.9Zn-0.5In, Sn-3.7Ag-0.9Zn-0.5Ce and Sn-xAg-0.9Zn(x=0.3, 0.5, 2.0, 3.0) alloys by impression creep show that the steady-state impression creep rate are in line with the constitutive equationε& = Aσn exp[ ? Q/( RT)], and the creep rate growth with the increase of stress and temperature.(3) The Sn-3.7Ag-0.9Zn alloy creep resistance enhanced obviously by added 0.5wt.% In and Ce-rich rare earth elements respectively. But added 0.5wt.% Al the creep resistance reduced. With the increased of Ag contents, the creep resistance of hypo eutectic Sn-xAg-0.9Zn (x=0.3, 0.5, 2.0, 3.0) alloys gradually strengthened.(4) The impression creep mechanism of Sn-3.7Ag-0.9Zn, Sn-3.7Ag-0.9Zn-0.5RE and Sn-xAg-0.9Zn(x=0.3, 0.5, 2.0, 3.0) main by dislocation climb, but the dislocation climb rate controlled by different mechanism. The the dislocation climbing rate of Sn-3.7Ag-0.9Zn lead-free solder is dominated by the grain boundary sliding process in Sn matrix, and the Sn-3.7Ag-0.9Zn-0.5RE lead-free solde is dominated by dislocation pipe diffusion process. To the Sn-xAg-0.9Zn(x=0.3, 0.5, 2.0, 3.0) lead-free solders the dislocation climbing rate is dominated by the grain boundary sliding process in Sn matrix at x=0.3 and 0.5, and by dislocation pipe diffusion process at x=0.3 and 0.5.(5) The influence on the impression creep mechanism of the Sn-3.7Ag-0.9Zn laed-free solder are dissimilar at different temperature by In elements added. At the temperature of 60℃and 80℃, the impression creep mechanism controlled by dislocation climb displacement, the dislocation climbing rate is dominated by dislocation pipe diffusion process , while at the temperature of 100℃and 120℃, the impression creep mechanism controlled by dislocation slip, the dislocation slipping rate is dominated by the grain boundary sliding process in Sn matrix.