Corrosão e refusão superficial à laser de ligas Sn-Ag-Cu
The study, selection and feasibility of non-toxic alloys for soldering electronic microcomponents are urgent and necessary demands in a context of accelerated technological advancement and Industry 4.0. Alternative lead-free solder alloys such as Sn-Ag-Cu (SAC) system alloys have stood out for th...
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| Formato: | Dissertação |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/52289 |
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| Resumo: | The study, selection and feasibility of non-toxic alloys for soldering electronic
microcomponents are urgent and necessary demands in a context of accelerated
technological advancement and Industry 4.0. Alternative lead-free solder alloys such as
Sn-Ag-Cu (SAC) system alloys have stood out for this application, as they have good
wettability on metallic substrates, high creep strength and melting temperature close to
the eutectic Sn-37wt.%Pb alloy, traditionally used in these situations. Laser surface
treatments result in significant microstructural changes, but studies for Sn-based alloys
are scarce in the literature. In this sense, the present research aims to understand the
microstructural characteristics and the respective hardness of the Sn-1wt.%Ag0.7wt.%Cu (SAC107) and Sn-3wt.%Ag-0.7wt.%Cu (SAC307) alloys treated by Laser
Surface Remelting (LSR). The corrosion resistances of the as-cast samples of SAC107
and SAC307 alloys have also been analyzed. In order to understand the solidification
paths of the alloys, such as solidification interval and transformation temperatures,
thermodynamic calculations were performed via the Thermo-Calc software.
Microstructural characterization was performed using optical microscopy (OM),
scanning electron microscopy (SEM) and the Electron Backscatter Diffraction (EBSD)
technique. The corrosion tests were made possible by potentiodynamic polarization, in
addition to the Vickers microhardness tests. The increase in Ag content slightly reduced
the liquidus temperature (TL), not changing the solidus (TS) and eutectic (TE)
temperatures. As-cast microstructures are composed of Sn-rich dendrites surrounded by
a ternary eutectic mixture β-Sn+Ag3Sn+Cu6Sn5. An epitaxial growth has been observed
at the base of the Laser remelted pools, as well as a significant microstructure
refinement in relation to the microstructural scale of the substrate (as-cast), of 98.5%
and 99.4%, for the SAC107 and SAC307 alloys, respectively, associated at cooling rates
of the order of 102
°C/s. Microhardness increases of 64.35% and 67.35% were noted for
SAC107 and SAC307 alloys, respectively, from coarse microstructures to refined
microstructures obtained by Laser. The polarization curves showed a more active
behavior of samples with coarser microstructures for both SAC alloys. SAC307 alloy
exhibited greater corrosion resistance than SAC107 alloy. |
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