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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 17    Special 1    November 2007

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Microstructures and properties of Sn-Ag-Cu lead-free
 solder alloys containing La
ZHOU Ying-chun(周迎春), PAN Qing-lin(潘清林), HE Yun-bin(何运斌), LIANG Wen-jie(梁文杰)
LI Wen-bin(李文斌), LI Yun-chun(李运春), LU Cong-ge(路聪阁)

School of Materials Science and Engineering, Central South University, Changsha 410083, China

Abstract:Trace amounts of La were utilized to improve the melting behaviors, microstructures, tensile properties and microhardness of Sn-3.0Ag-0.5Cu lead-free solder alloy. La has little effect on the melting behavior of Sn-3.0Ag-0.5Cu alloy according to the differential thermal analysis (DTA) tests. The X-ray diffraction (XRD) patterns show that β-Sn, Ag3Sn and Cu6Sn5 coexist in the as-cast solder alloys and LaSn3 phases emerge when adding 0.4% La. The microstructures modified by La are more uniform and much finer than that of baseline alloy, and the coarse LaSn3 particles with complex dendrites are observed by optical microscopy (OM) and scanning electron microscopy (SEM) when the addition of La is up to 0.4%. The composition of the LaSn3 phases is identified by energy-dispersive spectroscopy (EDS). There are considerable improvements in mechanical properties with 0.05% and 0.1% addition, but degenerations by adding 0.4%La. The Vickers microhardness of β-Sn and eutectic area are both enhanced with the addition of La and the microhardness of LaSn3 is much larger than those of β-Sn and eutectic area.

 

Key words: lead-free solder; Sn-Ag-Cu alloy; rare earth element; La; tensile properties

ISSN 1672-7029
CN 43-1423/U

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