Herein, the eutectic Al–11 wt% Si–5 wt% Ni alloy, directionally solidified under transient heat‐flow conditions, is comparatively evaluated in relation to the binary Al–11 wt% Si and Al–5 wt% Ni ...alloys. Correlations are developed relating the solidification cooling rate, primary dendritic spacing, and tensile properties. The Al3Ni intermetallic compounds (IMCs) are shown to have a morphological transition from plate‐like to fishbone for Ṫ < 6 °C s−1. Experimental Hall–Petch‐type equations are proposed relating yield and ultimate tensile strengths to λ1. Moreover, both the quality index (QI), which depends on the determined tensile properties, and the fishbone/plate‐like ratio (FPR) of the Al3Ni IMCs are plotted simultaneously as a function of Ṫ. This procedure permits three different regions to be determined relating solidification operational parameters to microstructural features and a quality parameter, according to the morphologies of the Al3Ni IMCs, namely (I) plate‐like, (II) fishbone rising, and (III) fishbone prevalence.
There is a keen interest of the automotive industry in AlSiNi‐based piston alloys, but there remain some gaps in the understanding of their microstructure evolution along solidification. Herein, an unsteady‐state directional solidification technique is used to develop correlations relating the solidification cooling rate, primary dendritic spacing, and tensile properties of a eutectic Al–11%Si–5%Ni alloy.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The use of Al for replacing high-cost alloying metals, like Ag, Bi, and Cu, as the second major element in Sn-based alloys, arises as a promising alternative for the development of low-cost Pb-free ...solder alloys. To date, however, the interfacial characteristics of Sn–Al solder joints in electronic substrates remain barely explored. Thus, the present study focuses on an understanding of the mechanisms affecting the heat transfer efficiency between a Sn–Al eutectic alloy and two types of substrates, establishing correlations with the microstructure evolution. Results of solidification experiments coupled with mathematical modeling demonstrate an interfacial thermal conductance between the Ni substrate and the Sn-0.5mass%Al alloy higher than that observed for the Sn–Al/Cu couple. Furthermore, Al-rich intermetallics are shown to occur at the interfacial reaction layers for both tested conditions. While dendritic and dendritic/cellular morphologies predominate in the solidification of the Sn–Al eutectic alloy in a Cu substrate, the better heat extraction through the Ni substrate induces the growth of refined high-cooling rate cells. Then, growth laws relating the length scale of the Sn-matrix, represented by cellular or primary dendritic spacings, to solidification thermal parameters such as cooling rate and growth rate are proposed.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The development of alloys suitable for engine bearings demands not only reducing the amount of wear as well as increasing the load carrying capability due to both engines stop/start systems and ...sudden rise in load or velocity. Al-Sn based alloys are well-known for having excellent tribological and mechanical properties fulfilling these requirements: Sn is a self-lubricating component and addition of third elements should increase the strength of the Al-rich matrix. The current study focuses on interrelations of microstructure of directionally solidified Al-Sn(Cu; Si) alloys and mechanical/tribological properties. In order to analyze the influence of alloy Sn content on the tribological behavior of these ternary alloys, ball-on-disc wear tests were performed under dry sliding conditions. Correlations between tensile strength, elongation and wear volume and the primary dendritic arm spacing (λ1) have been determined. The worn samples were analyzed by scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) and the wear scar topographies by a confocal profilometer. The analysis of the worn surfaces revealed a change from abrasive to adhesive wear mechanism for Al-Sn-Cu alloys and only adhesive one for Al-Sn-Si alloys. For Al-Sn-Cu alloys, the best wear resistance was observed to be related to coarser microstructures whereas refined microstructures improved the tensile properties, indicating an inverse trend between tensile and tribological properties. The wear resistance of the Al-Sn-Si alloys were shown not to be affected by the size of λ1, however the tensile strength is shown to increase significantly with the decrease in λ1.
Display omitted
•Al-Sn-Si; Cu alloys microstructure: dendritic Al-matrix, Sn pockets and Si; Al2Cu particles.•The lower the dendritic spacing, λ1, > the tensile strength of Al-Sn-(Cu; Si) alloys.•The higher λ1, the higher the wear resistance for Al-Sn-Cu alloys.•Experimental equations relating wear volume/tensile properties vs. λ1 are proposed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Eutectic Al-Ni alloys are widely faced as materials to be considered for advanced structural components. Nevertheless, still there is a lack of research on microstructural aspects of the eutectic ...Al-6.3 wt%Ni alloy and important points need to be addressed, such as, the morphology of the unsteady solidified eutectic, size and distribution of phases under different solidification cooling rates and the effects of the resulting microstructural features on mechanical properties. As such, in the present study, an Al-6.3 wt%Ni alloy is directionally solidified under a wide range of cooling rates and the resulting microstructure is shown to be formed by eutectic colonies. Three general microstructural features characterize the colony: a fine central zone composed of fibrous α-Al + Al3Ni eutectic, a boundary coarse zone formed by lamellar eutectic, and an Al-rich zone delimiting the colony. A quantitative analysis relating solidification thermal parameters to Al3Ni and colony spacings is outlined. Furthermore, the evolution of tensile properties as a function of these spacings was examined, and the highest strength and elongation of 160 MPa and 15%, respectively, are associated with an ultrafine bimodal structure formed by eutectic colonies with 55 μm in spacing containing very fine fibers (300 nm in spacing) and lamellae with 750 nm in spacing.
Display omitted
•Eutectic colonies typify the microstructure of directionally solidified Al-6.3 wt%Ni alloy.•The colony has a bimodal structure: fine Al3Ni fibers (center)/coarse lamellae (boundary).•Growth laws: colony/inter-fiber/lamellar spacings vs. growth/cooling rates are proposed.•Experimental equations relating tensile properties vs. colony spacing are proposed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In electronic devices the solder joint is exposed not only to the air but also to moistures and other corrosive media such as chlorine and sulfur compounds. Bi–Ag alloys meet the melting temperature ...requirement to be classified as high-temperature solders, therefore, knowledge of corrosion behavior is important for a long-term reliability of Bi–Ag solder connections. However, corrosion studies of Bi–Ag alloys are quite restricted in the literature. In this study, the role of the representative length scale of the microstructure as well as of the effects of Ag segregation on the resulting corrosion behavior of Bi–4 wt% Ag alloy samples are investigated. Cyclic potentiodynamic polarization and electrochemical impedance spectroscopy measurements were performed, and an equivalent circuit was also proposed to simulate the electrochemical corrosion behavior. All the used techniques indicated a tendency of better corrosion resistance associated with the sample having coarser microstructure and less Ag content.
Graphic abstract
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
One of the most important parameters in the foundry design of castings is the heat transfer coefficient at the casting/mold surface (
h
), which significantly affects the solidification cooling rate ...and defines the as-cast microstructure and, consequently, its properties. The inverse heat transfer problem (IHTP) is a needed task to be solved in many casting processes to evaluate this coefficient. In this work, four different nature inspired algorithms genetic algorithm (GA), evolutionary strategy (ES), artificial immune system (AIS) and particle swarm algorithm (PSO) have been integrated to a numerical model of solidification to solve the IHTP problem with a view to evaluating the transient profile of
h
during solidification of three different cylindrical casting setups (outward, inward and upward). The aim is to reduce the number of iterations to achieve successful results by the association between metaheuristics and different sets of h values. Therefore, an objective function was modeled to match the temperatures predicted by the numerical model to those of experimental measurements. Sets of 10, 20, 50, 100 and 200 h values used to compose its transient profile have been evaluated by the four metaheuristics approaches aiming to characterize each casting situation.
Full text
Available for:
CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Zn-Mg alloys are considered to have potential application in bone implants, since both metals are biocompatible and have biodegradable characteristics. Adding Mg to Zn can boost mechanical and ...corrosion resistances. However, the literature is very limited on quantifying the interrelation of solidification parameters, microstructural features and mechanical/corrosion properties of Zn-Mg alloys. The present study examines the interrelations of alloy Mg content, macrosegregation effects, morphology and scale of the matrix and eutectic phases, nature of intermetallics and tensile and corrosion properties of near-eutectic Zn-Mg alloys. The alloys samples are obtained by unsteady-state directional solidification resulting in a wide range of solidification thermal parameters and microstructures. We examine microstructural features of both dendritic and complex regular eutectic phases. It is shown that the eutectic exhibits a bimodal pattern with neighboring areas of coarse and fine lamellae. Experimental growth laws relating the primary, secondary and eutectic spacings to the solidification cooling rate and growth rate are proposed. Hall-Petch type equations are derived expressing tensile strength and elongation to dendritic and eutectic spacings. Electrochemical parameters determined by polarization curves during corrosion tests and SEM analyses of corroded areas have shown that the alloy having an essentially eutectic microstructure is associated with better corrosion resistance.
Display omitted
•The Zn-Mg eutectic has bimodal morphology: areas of fine and coarse lamellae and spiral structures.•Growth laws: dendritic/lamellar spacings vs. growth/cooling rates are proposed.•Experimental equations relating tensile properties vs. dendritic/lamellar spacings are proposed.•Best tensile/corrosion properties > alloy with higher eutectic fraction and finer lamellar spacing.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Due to its strong influence on service life of manufactured parts, corrosion resistance is an important factor to consider when designing Al alloys for engineering applications. With this in mind, ...the present study focuses on understanding the role of microstructure features in the corrosion behavior of an Al-10wt.%Sn-5wt.%Zn alloy. Samples with different microstructural length scales were subjected to corrosion tests, which were performed using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. An equivalent circuit analysis was also carried out. The results revealed a relatively high electrochemical activity of the studied alloy. Furthermore, coarsening in microstructure showed a slight tendency towards improvements in the corrosion resistance, that is, coarser microstructures composed by Al-rich dendrites surrounded by Sn–Zn constituent particles were comparatively less prone to corrosion degradation than finer ones. Finally, the proposed equivalent circuit model is shown to have good agreement with the experimental EIS measurements.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work deals with the development of quantitative correlations of hydrogen evolution performance with solidification microstructural and thermal parameters in Al–1Sn, Al–2Sn, Al–1Fe, and Al-1.5Fe ...wt.% alloys. The cellular growth as a function of growth and cooling rates is evaluated using power type experimental laws, which allow determining representative intervals of microstructure length scale for comparison purposes with the results of immersion tests in 5 wt%NaOH solution. For both Al alloys systems, hydrogen evolution becomes slower as the alloy solute content increased. However, for a given alloy composition, whereas a more homogeneous distribution of Sn-rich particles promotes faster hydrogen generation using Al–Sn alloys, coarsening of Al6Fe IMCs (intermetallic compounds) fibers favors hydrogen production using Al–Fe alloys. When solidification conditions that result in a range of cellular spacings within 16 and 19 μm are considered, the specific hydrogen production of the Al-1wt.%Fe alloy is higher than that of the other studied alloys.
Display omitted
•Specific H2 generation rate is evaluated in Al alloys with low Sn and Fe contents.•Microstructure features-hydrogen generation rate correlations are proposed.•Homogeneous distribution of Sn-rich particles in Al–Sn alloys favors H2 production.•Coarse Al6Fe IMCs fibers in Al–Fe alloys are related to faster H2 generation.•Alloy/mold heat transfer coefficient is the key factor for microstructure design.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
