Sn-0.5Cu(-x)Al solder alloys: microstructure-related aspects and tensile properties responses

In this study, experiments were conducted to analyze the effect of 0.05 and 0.1 wt.% Al additions during the unsteady-state growth of the Sn-0.5wt.%Cu solder alloy. Various as-solidified specimens of each alloy were selected so that tensile tests could also be performed. Microstructural aspects such as the dimensions of primary, lambda(1), and secondary, lambda(2), dendritic arrays, and intermetallic compounds (IMCs) morphologies were comparatively assessed for the three tested compositions, that is, Sn-0.5wt.%Cu, Sn-0.5wt.%Cu-0.05wt.%Al, and Sn-0.5wt.%Cu-0.1wt.%Al alloys. Al addition affected neither the primary dendritic spacing nor the types of morphologies identified for the Cu6Sn5 IMC, which was found to be either globular or fibrous regardless of the alloy considered. Secondary dendrite arm spacing was found to be enlarged and the eutectic fraction was reduced with an increase in the Al-content. Tensile properties remained unaffected with the addition of Al, except for the improvement in ductility of up to 40% when compared to the Sn-0.5wt.%Cu alloy without Al trace. A smaller lambda(2) in size was demonstrated to be the prime microstructure parameter associated with the beneficial effect on the strength of the Sn-0.5wt.%Cu(-x)Al alloys92CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO AMAZONAS - FAPEAM407978/2018-6; 307830/2017-92015/11863-5; 2016/18186-1; 2017/12741-6sem informaçã

Microstructure, thermal parameters and mechanical properties analysis in the solidification of high copper Al-(x)%Cu-7%Si alloys

Ternary Al-15%Cu-7%Si and Al-22%Cu-7%Si alloys specimens were obtained by transient directional solidification (DS). This technique is able to provide a very large range of cooling rates and microstructures to be correlated to each other. Overall the microstructures of the directionally solidified samples are constituted by an α -Al dendritic matrix surrounded by two eutectic, that is a binary eutectic, consisting of Si and α -Al, and a bimodal eutectic consisting of cellular type binary eutectic colonies (α-Al + Al2Cu) in a ternary eutectic matrix consisting of (α -Al + Al2Cu + Si). Specially in the case of the Al-22%Cu-7%Si alloy, primary Si particles were also observed. A complete analysis of the dendritic length scale was performed so that relationships of primary and secondary dendritic spacing with cooling rate and growth rate could be derived. The mean dendritic spacing of the DS samples varied: from 85 to 337 μm (λ1) / from 5,7 to 17,7 μm (λ2)/ from 5,5 to 1 7,3 μm (λ3) and from 93,6 to 249 μm (λ1) / from 9,8 to 18,1 μm (λ2) / from 6,6 to 15,1 μm (λ3) for the Al-15wt.%Cu-7wt.%Si and Al-22wt.%Cu-7wt.%Si, respectively. Higher tensile and compressive strengths are associated with the DS alloy containing lower copper content. Furthermore, mechanical properties have been determined for various samples related to different dendritic spacing values so that Hall-Petch type equations could be proposed.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Amostras das ligas de Al-15%Cu-7%Si e Al-22%Cu-7%Si foram produzidas por solidificação direcional em regime transiente de extração de calor. Esta técnica é capaz de produzir um amplo espectro de taxas de resfriamento e microestruturas, os quais podem ser correlacionados entre si. De forma geral as microestruturas das amostras solidificadas direcionalmente obtidas foram constituídas de fase α -Al na forma dendrítica circundada por dois tipos de eutéticos, um binário, composto por α-Al + Si, e um eutético bimodal, composto por colônias eutéticas binárias (α-Al + Al2Cu), dispostas em uma matriz eutética ternária, constituída por α -Al + Al2Cu + Si. Especialmente no caso da liga Al-22%Cu-7%Si, foi observada a ocorrência de partículas de Si primário. Uma análise completa sobre o dimensionamento dos espaçamentos dendríticos foi realizada no intuito de determinar relações entre espaçamento dendrítico primário e secundário com taxa de resfriamento e velocidade de deslocamento da isoterma liquidus. Os espaçamentos dendríticos médios das amostras direcionalmente solidificadas variaram: de 85 à 337 μm (λ1) / de 5,7 à 17,7 μm (λ2)/ de 5,5 à 17,3 μm (λ3) e de 93,6 à 249 μm (λ1) / de 9,8 à 18,1 μm (λ2) / de 6,6 à 15,1 μm (λ3) para as ligas Al-15%Cu-7%Si e Al-22%Cu-7%Si, respectivamente. As maiores resistência à tração e à compressão foram visualizadas na ligas direcionalmente solidificadas com menor concentração de Cu devido à capacidade das dendritas de Al acomodar tensão e dificultar a propagação de microtrincas. Além disso, propriedades mecânicas foram determinadas para várias amostras e relacionadas a diferentes valores de espaçamentos dendríticos por meio da proposição de equações tipo Hall-Petch.CNPq: 132492/2017-2FAPESP: 2017/12741-

Thermal analysis during solidification of an Al-Cu eutectic alloy : interrelation of thermal parameters, microstructure and hardness

Eutectic alloys are considered promising candidates for high-temperature structural applications. In spite of this, quantitative examination of the effect of the length scale of the eutectic microstructure on mechanical properties remains a challenge. In this sense, assessments of morphology, size and distribution of the phases forming the eutectic mixture, solidified under transient regime and different cooling conditions, endure necessary. In the present study, a large spectrum of cooling rates has been obtained during unsteady-state directional solidification of an Al-33mass% Cu alloy. The main techniques utilized were: optical microscopy; scanning electron microscopy with X-ray energy-dispersive spectroscopy, X-ray fluorescence spectroscopy and Vickers hardness (HV). The resulting microstructures related to various solidification cooling rates are shown to be formed by eutectic colonies. Three microstructural zones constitute the colony, that is, a fine central regular lamellar Al-Al2Cu eutectic, an intermediate narrow wavy lamellar eutectic and a coarse boundary eutectic zone. Iron impurity appears to be able to degenerate the eutectic into a more randomly distributed microstructure. The colonies' morphology exhibits a transition from regular to platelike cells with the increase in cooling rate. Furthermore, the evolution of hardness as a function of the colony spacings is outlined. The highest hardness of 200 HV is related to an ultrafine bimodal structure formed by platelike eutectic colonies with 13 mu m in spacing with very fine lamellae of 330nm in spacing1373983996CNPQ - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulonão tem2017/12741-

Sn-Bi(-Ga) TIM alloys: microstructure, tensile properties, wettability and interfacial reactions

In the present study, the main purpose is to examine the quality of the interface formed between either binary Sn-Bi or ternary Sn-Bi-2wt.%Ga Thermal Interface MaterialTIM alloys and a copper (Cu) substrate. The characteristics of the formed intermetallic compound (IMC) films were analyzed in the as-soldered joints, as well as during isothermal heat treatments at 100 degrees C for long periods of time. Thermo-Calc computations were also used in return for a better comprehension of the mechanisms involved, including, for instance, those related to the presence of Ga within the interdendritic regions. This can be explained by the increase in the Ga-amount in the liquid-phase with the progress of solidification. In an effort to address the wettability issue, the contact angles between the molten alloy and the Cu substrate were also determined. Finally, tensile tests were performed in order to evaluate the effects of the minor Ga additions in the alloy's overall mechanical properties. Despite unsound alloy mechanical properties, gallium (Ga) additions effectively suppress the formation of the CuSn intermetallic by replacing it with a Cu9Ga4 IMC layer in the as-soldered material, which grew with less deleterious morphology and finer thicknesses48847734788CAPES - Coordenação de Aperfeiçoamento de Pessoal e Nível SuperiorFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulo2017/12741-6sem informaçãoThe authors are grateful to FAPESP (São Paulo Research Foundation, Brazil: Grant 2017/12741-6) for their financial support. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brazil (CAPES