Banca de QUALIFICAÇÃO: IONE AMORIM BEZERRA NETA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : IONE AMORIM BEZERRA NETA
DATE: 07/05/2024
TIME: 09:00
LOCAL: Link sala Google Meet: meet.google.com/ihf-qrhs-agv
TITLE:

Directional solidification of Sn-9wt.%Zn-x(Al, Bi) alloys: thermal parameters, microstructure, corrosion and mechanical properties

KEY WORDS:

Sn-Zn-Al alloys; Sn-Zn-Bi alloys; Solidification; Microstructure; Mechanical properties.

PAGES: 173
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Metalurgia Física
SPECIALTY: Transformação de Fases
SUMMARY:

The search for viable solutions for replacing Sn-Pb alloys in soldered joints of electronic microcomponents has received special attention in recent years. In this sense, the Sn-9wt.%Zn eutectic alloy is a promising alternative, as it has a eutectic temperature (198°C) similar to the              Sn-38wt.%Pb alloy, low cost and excellent mechanical properties. However, these alloys exhibit disadvantages such as low corrosion resistance and low wettability, which limits their practical use in soldering operations. One of the improvement alternatives is modification with aluminum (Al) and bismuth (Bi). These elements promote changes in microstructure, mechanical properties and corrosion resistance. Therefore, the present work aims to study the effect of adding Al (0.5% and 2.0% by mass) and Bi (3.0% and 6.0% by mass) on the thermal parameters of solidification (rate cooling rate-Ṫ_L and growth rate-V_L), as-cast microstructure, macrosegregation, corrosion resistance, mechanical properties and fracture modes of the directionally solidified (DS) Sn-9wt.%Zn-X alloys. The samples were characterized by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Fluorescence (XRF), X-ray Diffraction (XRD), in addition to analysis of tensile mechanical properties. The effect of microstructures on corrosion resistance will be analyzed using electrochemical impedance spectroscopy (EIE) and potentiodynamic polarization. Thermodynamic calculations were performed by the CALPHAD method via Thermo-calc software, in order to evaluate the solidification sequence, phase compositions and phase transformation temperatures. The additions of Al and Bi to the Sn-9wt.%Zn binary alloy increased the T_L values and reduced the T_E values, increasing the solidification range for the alloys examined. The Sn-9wt.%Zn-3.0wt.%Bi alloy was the only one to exhibit columnar growth in the macrostructure, with a Columnar-Equiaxial Transition (TCE) being observed in the rest of the alloys. Eutectic cell growth has been observed for the Sn-Zn-Al and Sn-Zn-Bi alloys, composed of the Sn+Zn+Al and Sn+Zn+Bi phases, respectively. Only the 2wt.%Al content was able to change the microstructural scale, subtly refining the eutectic cellular arrangement. On the other hand, Bi additions refined the eutectic cell arrangement. The morphologies of the Bi particles and the α-Zn phase (of the eutectic mixture) were shown to be dependent on the solute content and cooling rate. Al additions promoted a reduction in both the ultimate tensile strength (σ_u) and elongation-to-fracture (δ). On the other hand, Bi additions promoted an increase in σ_u and a reduction in δ. In comparison to the Sn-9wt.%Zn alloy, it is noted that Al additions did not change the fracture mode, remaining ductile, while Bi additions induced a brittle fracture mechanism through cleavage.

COMMITTEE MEMBERS:
Presidente - 2345599 - BISMARCK LUIZ SILVA
Externo ao Programa - 1652765 - MAURÍCIO MHIRDAUI PERES - UFRNExterno ao Programa - 1938946 - NICOLAU APOENA CASTRO - UFRNExterna à Instituição - SUYLAN LOURDES DE ARAÚJO DANTAS