Solidification Thermal Parameters Research Articles

Zn additions modifying microstructure, thermal parameters and cytotoxicity of Sn-0.7Cu eutectic solder alloys

Alloys from the SnCu systems have superior properties as compared to the SnPb alloys, such as mechanical and corrosion resistance. However, SnCu alloys still exhibit low oxidation resistance, poor wettability and low reliability. One way to optimize such properties is by adding alloying elements, such as zinc. Zn is generally used in Pb-free solder alloys to minimize intermetallic compound growth in soldered joints, refine the microstructure and increase mechanical strength, in addition to reducing the final cost. The addition of Zn is motivated by the effects it promotes such as microstructural refining, suppression of intermetallics in the substrate/alloy reaction layer, increase in fluidity and mechanical properties. Therefore, this study aims to understand the effects of Zn additions (0.2 and 0.5 in wt%) on solidification thermal parameters (growth rate-V and cooling rate-Ṫ), macrostructure, microstructure, phase transformation, macrosegregation and cytotoxicity in directionally solidified eutectic Sn-0.7wt.%Cu alloy under transient heat flow regime of solidification in copper sheet. Thus, the samples have been characterized by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD). The CALPHAD (CALculation of PHAse Diagrams) method by Thermo-calc software was used to generate property diagrams and isopleths. Cytotoxicity analysis was performed based on cell viability with incubation periods of 15 and 30 days for the alloys, with subsequent exposures of the extracts for 24 and 48 h. The Zn additions caused slight changes in the phase transformation temperatures of the Sn-Cu-Zn alloys. Macrostructures exhibiting columnar-to-equiaxed transition (CET) were observed for the Sn-Cu-Zn alloys. The microstructures of the Sn-Cu-Zn alloys were predominantly dendritic with a matrix rich in tin (β-Sn) surrounded by a eutectic mixture of the β-Sn + Cu6Sn5 + CuZn phases. After CET on Sn-Cu-Zn castings, low velocity eutectic cells have been observed. Moreover, Zn additions refined and did not change the dendritic arrangement of the Sn-Cu-Zn alloys, when compared to the Sn-0.7wt.%Cu alloy. However, increasing the Zn content did not affect the microstructural scale in the ternary alloys when compared to each other. The variations in the microstructural scale did not influence the toxicity of the examined alloys, but factors such as incubation time and chemical composition did. In general, Zn improved the cell viability of the Sn-Cu-Zn alloys, but still with moderate cytotoxic levels.

Microstructure, Hardness, and Linear Reciprocating Sliding Wear Response of Directionally Solidified Al–(2.5, 3.5, 4.5)Cu–(0.25, 0.50)Cr Alloys

Aluminum alloys containing transition metal alloying elements have attracted interest from researchers. The effect of Cr additions of 0.25 and 0.50% on the thermal profile, microstructure, hardness, and linear reciprocating sliding wear response of as-cast hypoeutectic Al–Cu alloys with 2.5, 3.5, and 4.5% Cu (wt.%) was investigated. The binary Al–Cu and ternary Al–Cu–Cr alloys were directionally solidified under upward non-steady state heat transfer conditions using a dedicated solidification apparatus. Thermal analysis based on differential thermal analysis (DTA) and cooling curve profiles was performed to determine solidification thermal parameters such as Liquidus temperature (TL), transformation enthalpy (ΔH), and liquid cooling rate (ṪL). Samples extracted from the solidified ingots were submitted to optical microscopy, hardness measurement, and linear reciprocating sliding wear test using a high-frequency reciprocating rig (HFRR). The results showed a decrease at the beginning of solidification (TL) and of the transformation enthalpy (ΔH) when both alloy Cu and Cr contents increased, with a higher influence of Cu. The addition of Cu decreased cooling rates, whereas the increase in the alloy Cr concentration showed an opposite behavior, increasing cooling rates. The refinement of the primary dendrite arm spacing (λ1), as a consequence of the increase in alloying elements and solidification cooling rates, enhanced the hardness of the alloys, with the maximum value of 58 HB achieved in the ternary Al–4.5Cu–0.50Cr alloy. The wear tests indicated a better response to wear associated with microstructure refinement for the alloys with 2.5% Cu, for both Cr contents, an almost constant behavior for the 3.5% Cu alloys, and an opposite performance for the alloys with 4.5% Cu alloys that showed better wear resistance with coarsening of the λ1 and with the increase in the amount of the eutectic microconstituent.

Microstructure and Tensile Strength of an Al-Si-Fe-V Alloy: Vanadium and Solidification Thermal Parameters as Recycling Strategies

One of the greatest challenges facing the recycling of Al-based alloys is handling Fe incorporation. The formation of Fe-rich phases has negative impacts on the mechanical behavior and may limit the usage of recycled alloys. In this context, V addition is regarded as a potential solution since it can inhibit the formation of such phases. However, the microstructure evolution of V-modified Al-based alloys is not fully understood, especially when different solidification cooling regimes are considered. Thus, this work investigates the microstructure and tensile properties of an Al-7Si-1Fe [wt.%] alloy modified with a 0.5 wt.%V addition. Directionally solidified samples were produced and subjected to microstructure analysis and tensile tests. It was found that the addition of V reduces the fraction of β-AlFeSi particles because of the formation of new V-rich phases. This was determinant to improve the tensile properties for faster cooling conditions during solidification. For moderate and slow cooling regimes, however, the V-containing alloy had a less favorable mechanical behavior due to the formation of larger β-AlFeSi particles. Finally, quantitative relationships are proposed for the prediction of tensile properties from microstructural parameters using multiple linear regression analysis.

Casting Alloy Design and Characterization

Metal casting processes routinely used in the foundry industry (e.g., gravity or pressure casting) are subject to a wide range of operational parameters. Since there is a close correlation between solidification conditions, microstructure, and properties, the effects of the solidification thermal parameters and alloying elements on microstructure designs and the resulting properties in cast alloys have stimulated new research interest. Thus, this Special Issue aims to collect research articles focused on the design and characterization of cast alloys, especially on the interrelationship between solidification, microstructure, and properties; both experimental and theoretical research are welcome for contribution.

Hypereutectic Zn–Al Alloys: Microstructural Development under Unsteady-State Solidification Conditions, Eutectic Coupled Zone and Hardness

The present study investigates the effects of Al content and solidification thermal parameters on the microstructural development under transient heat flow conditions for two hypereutectic Zn–Al alloys: Zn-6wt.%Al and Zn-11wt.%Al. The alloys were directionally solidified and had experimental cooling profiles monitored permitting cooling rates and growth rates to be determined along the length of the directionally solidified (DS) castings. The microstructure of the Zn-6wt.%Al alloy is shown to be formed by eutectic colonies, constituted by a eutectic mixture of (Zn) and (Al′) phases in the form of lamellae and the Zn-11wt.% Al alloy by the pro-eutectic (Al′) dendrites and the eutectic mixture in the interdendritic regions. Growth laws are experimentally determined relating eutectic and dendritic spacings to the growth rate and cooling rate. A diagram exhibiting the coupled zone of Zn–Al alloys as a function of cooling rate is proposed, which shows different microstructural morphologies influenced by composition and thermal parameters, that is, growth rate and the temperature gradient, synthesized by the cooling rate (Ṫ = G.V). The microhardness of both Zn-6wt.%Al and Zn-11wt.%Al alloys were shown not to depend on the length scale of the resulting microstructure.

Microstructural Patterns, Microsegregation, Porosity, and Mechanical Properties of Hypoeutectic Al-Fe Alloy, and its Dependency with Solidification Thermal Parameters

Al-Fe alloys are usually used as packaging and structural materials, but in the recent years, there have been considered for possible applications in aerospace field. The solidification sequence in pure aluminum containing 1 wt.% Fe is described in term of the formation of macrostructure, microstructure, microsegregation, porosity and mechanical properties. This material was studied in the upward unidirectional solidification system under transient heat flow conditions. Differences in microstructure, microsegregation, porosity and mechanical properties such as ultimate tensile strength, elongation and microhardness, due to the thermal parameter effects were observed and discussed. Experimental growth laws relating cellular spacing to the cooling rate and solidification speed have been determined, indicating that the increase in thermal parameter have induced a refinement effect on cell morphology. Microsegregation profiles of Fe solute were experimentally determined from the central region of the cell to the intercellular region under different solidification speeds. The Fe microsegregation determined from central region of the cell (FS = 0) to the intercellular region (FS = 1) show a growing profile, in any case considered. However, the profiles move upward with the increase in solidification speed, which indicates that Fe solubility in solid, increases with the increase in solidification speed. The effect of the solidification thermal parameters and cellular spacing on the porosity content were experimentally investigated. The value of porosity content increased along the casting. These results have pointed out that porosity content is affected by solidification parameters and cellular patterns. Further, measurable effects of the thermal parameters, cellular spacing and porosity content on the mechanical properties were experimentally determined. It stands out among experimental results the influence of porosity on the mechanical properties of as-cast material. In any case analyzed, mechanical properties increase with decreasing porosity content.

Criticism of the paper titled ‘Solidification thermal parameters, microstructural evolution and dendritic growth in an AlCuNi alloy’ by Correa et al.

Recently, Correa et al. [1] conducted experiments on the relationship between solidification parameters, including solidification time ts and secondary dendrite arm spacing λ2, for an Al-3wt.%Cu-3w...

Influence of the dendritic microstructure and β-Al5FeSi phase on the wear characteristics in a horizontally solidified Al-7Si-0.4Mg-1.2Fe alloy

In this work an Al-7Si-0.4Mg-1.2Fe alloy (wt.%) was subjected to a horizontal solidification experiment using a water-cooled solidification device equipped with thermocouples to obtain temperature vs. time data which in turn allowed solidification thermal parameters, such as growth and cooling rates (VL and TR, respectively), to be determined. In turn, tribological behavior of samples with different secondary dendritic spacing (λ2) and β-Al5FeSi platelets length (βFe) were assessed by means of dry sliding wear testing performed in a rotating fixed ball machine, with wear volume and rate (WV and WR, respectively) being the two main investigated wear parameters. Quantitative metallography by optical and scanning electron microscopy along with energy dispersive X-ray spectroscopy enabled both as-cast microstructures and worn craters to be characterized. More significant variations in wear resistance of the investigated alloy were found for ranges of λ2 and βFe that lie within 12−20 μm and 14–36 μm, respectively, with the coarsening of the microstructure constituted by Al-rich primary phase dendrites surrounded by α-Al + Si + θ-Mg2Si + β-Al5FeSi eutectic structures favoring reduced WV and WR values. For λ2 and βFe values higher than 24 and 48 μm, respectively, both WV and WR stabilize assuming constant values that depend on the sliding distance. In addition to power type equations relating λ2 and βFe to VL and TR, mathematical expressions for variations of WV and WR with λ2 and βFe are also proposed. Finally, a comparative analysis with the literature is presented.

Modifications on solidification thermal parameters, microstructure and hardness induced by Cu additions to a hypereutectic Zn[sbnd]8Al alloy

Binary ZnAl alloys are interesting alternatives when tensile strength and hardness performances are required. However, such alloys exhibit limitations on lubrication, ductility at room temperature and mechanical strength at high temperatures. It is known that small alloying additions of Cu to ZnAl alloys can modify the microstructure and properties such as creep and wear resistances, hardness, fluidity, and lubrication. In this sense, this work aims to study the effects of Cu additions on the solidification thermal parameters such as cooling and growth rates (ṪL/VL-liquidus isotherm and ṪE/VE-eutectic front), microstructure (dendritic and eutectic arrangements), and hardness of a hypereutectic Zn-8wt.%Al alloy. Techniques such as X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to characterize the as cast samples. The results show that the resulting microstructures consist of a eutectic matrix [(Zn) + (Al + Zn)] with lamellar and fibrous morphologies and τ’-Al4Cu3Zn intermetallic particles disseminated within the (Zn) phase; pro-eutectic Al-rich (Al') dendrites containing alternating lamellae of Al and Zn phases, which resulted from the eutectoid transformation [(Al')↔(Al) + (Zn)]. The Cu additions have coarsened the fibrous and lamellar eutectic of the binary Zn-8wt%Al alloy, with exception of the Zn-8 wt% Al-1.3 wt% Cu alloy, which showed a refinement of the fibrous eutectic for VE > 0.30 mm/s. Increase in hardness has been observed for both Cu-modified alloys due to the solid-solution strengthening mechanism and presence of the τ’-Al4Cu3Zn intermetallics. An expressive increase of about 73.4% has been observed due to the addition of 1.3% Cu, which is also related to lower eutectic fibrous spacings.

Microstructure Growth Morphologies, Macrosegregation, and Microhardness in Bi–Sb Thermal Interface Alloys

Due to the rising demand for thermal management technologies within the electronics industry, there has been an increased emphasis on developing new thermal interface materials (TIMs) with enhanced performance. Despite Bi‐based alloys having exhibited promising potential as TIMs in microelectronics cooling applications, understanding the microstructure evolution of these alloys and the consequent effects on the resulting properties still remains an essential task to be accomplished. Herein, a directional solidification technique is used to investigate microstructural features and Vickers microhardness of Bi(5–20) wt% Sb alloys with a focus on the roles of alloy composition, solidification thermal parameters, and macrosegregation. The results show the formation of aligned Bi‐rich dendrites in a broad range of cooling rates from about 0.2 to 25 °C s−1. In contrast, as the alloy Sb content increases, two morphological transitions in the Bi‐rich matrix are shown to occur as follows: trigonal pattern → irregular shape → trigonal pattern. Then, primary and secondary dendritic arm spacings are related to growth and cooling rates through experimental equations. Finally, the occurrence of macrosegregation along the length of the Bi–20 wt% Sb alloy casting is shown to be a key factor associated with the variation of microhardness.

Effect of solidification process parameters on dry sliding wear behavior of AlNiBi alloy

Abstract As-cast samples of the Al–3wt.%Ni–1wt.%Bi alloy resulting from the horizontal directional solidification process were subjected to the micro-abrasive wear test. The effects of the solidification thermal and microstructural parameters, such as the growth and cooling rates and the cellular and primary dendritic spacings (VL and TR; λ1 and λc; respectively), were evaluated in the wear resistance of the investigated alloy. The tribological parameters analyzed were the wear volume and rate (Vw and Rw). The solidification experiments and the wear tests were carried out by means of a water-cooled horizontal directional solidification device and a rotary-fixed ball wear machine, respectively. The results show lower Vw and Rw values correspond to finer microstructures and the Vw dependence on λ1 is characterized by an experimental mathematical equation. A better distribution of Bi soft droplets and Al3Ni hard intermetallic particles is observed within the finer interdendritic region and, in consequence, the better wear resistance is achieved in as-cast samples with dendritic morphology rather than cellular morphology. A transition of wear mechanism from adhesive to abrasive is observed.

Correlation between unsteady-state solidification thermal parameters and microstructural growth of Zn–8 mass% Al and Zn–8 mass% Al–XBi tribological alloys

In the present study, directionally solidification experiments are performed with Zn–8 mass% Al and Zn–8 mass% Al–X mass% Bi (X = 1.5, 2.3 and 3.0 mass%) alloys using a water-cooled solidification system, which permits a wide range of solidification cooling rates to be investigated in a single experiment. The microstructural phases of the ternary alloys are shown to be quite similar to those of the binary alloy, with equiaxed dendrites immersed in a matrix formed by fibers or lamellae of the Al/Zn eutectoid product, with the difference that the ternary alloys have Bi droplets disseminated into the matrix and dendrite branches. The dendrites, lamellae and fibers evolve from a refined microstructure at regions closer to the water-cooled bottom of the casting, to increasingly coarser microstructures toward the top. Experimental expressions relating the secondary dendritic arm spacing, the spacing between lamellae and the fiber spacing to solidification thermal parameters (growth and cooling rates) are derived. For the alloys having higher Bi content, a bimodal distribution of Bi droplets was shown to occur, with small droplets, consisting of lamellae and fibers, disseminated into the matrix and larger droplets between the dendritic branches.

Tailoring of Processing Parameters, Dendritic Microstructure, Si/Intermetallic Particles and Microhardness in As-cast and Heat-Treated Samples of Al7Si0.3Mg Alloy

In this work, solidification and T6-heat treatment experiments were performed with the Al7Si0.3Mg alloy in order to investigate the effect of processes parameters on the microstructure and microhardness (HV). A directional solidification device was used, and the solidification thermal parameters investigated were the growth and cooling rates (VL and TR). The heat treatment applied was the T6 (T6-HT), under the following conditions: solution treatment for 3 h at 520????????2 ??C, followed by quenching in warm water (70????????20 ??C), aging for 1, 2, 3 and 4 h at 155????????2 ??C and air-cooling. The microstructure observed in both as-cast and T6-heat treated samples is composed of a primary phase consisting of an Al-rich dendritic network and secondary eutectic phases, located within the interdendritic regions, formed by Si and Mg2Si particles and Fe-intermetallic phases. The dendritic microstructure was characterized by secondary dendritic spacing (??2) and, for both investigated samples, a single mathematical expression was proposed on the ??2 dependence with the position in the ingot. Spheroidized-like eutectic Si particles have been found in both analyzed samples for finer microstructures. Elements quantitative and qualitative microanalysis by SEM/EDS as well as HV measurement at the dendritic and interdendritic regions attest to the effectiveness of the T6-heat treatment. It is highlighted in this work that mathematical expressions have been proposed to characterize the HV dependence on aging time.

Interconnection between the solidification and precipitation hardening processes of an AlSiCu alloy

ABSTRACTHorizontal directional solidification and precipitation hardening experiments were performed with the Al5.5Si3Cu alloy. Solidification thermal and microstructural parameters such as growth and cooling rates (VL and TR, respectively) and the secondary dendrite arm spacing (λ2) were determined experimentally. As-solidified samples were selected and submitted to the T6-heat treatment (T6-HT). The T6-HT was carried out considering two solution times: 8 and 5 h at 490 ± 2°C, followed by quenching in warm water (60 ± 2°C), aging for 5 h at 155 ± 2°C and air-cooling. Higher HV values were observed for the solution time of 5 h. As highlights of this work, the influence of the processing parameters (VL, TR and λ2) on the distribution, morphology and size of the eutectic Si particles has been investigated.

Cellular-to-Dendritic and Dendritic-to-Cellular Morphological Transitions in a Ternary Al-Mg-Si Alloy

The study is focused on the influence of solidification thermal parameters upon the evolution of the microstructure (either cells or dendrites) of an Al-3wt%Mg-1wt%Si ternary alloy. It is well known that the application properties of metallic alloys will greatly depend on the final morphology of the microstructure. As a consequence, various studies have been carried out in order to determine the ranges of cooling rates associated with dendritic-cellular transitions in multicomponent alloys. In the present research work, directional solidification experiments were conducted using either a Bridgman (steady-state) device or another device that allows the solidification under transient conditions (unsteady-state). Thus, a broad range of cooling rates (Ṫ), varying from 0.003K/s to 40K/s could be achieved. This led to the identification of a complete series of cellular/dendritic/cellular transitions. For low cooling rate experiments, low cooling rate cells to dendrites transition happens. Moreover, at a high cooling rate, a novel transition from dendrites to high cooling rate cells could be observed for the Al-3wt%Mg-1wt%Si alloy. Additionally, cell spacing λC and primary dendritic spacing λ1 are related to the cooling rate by power function growth laws characterized by the same exponent (-0.55) for both steady-state and unsteady-state solidification conditions.

Effects of Thermal Variables of Solidification on the Microstructure, Hardness, and Microhardness of Cu-Al-Ni-Fe Alloys.

Aluminum bronze is a complex group of copper-based alloys that may include up to 14% aluminum, but lower amounts of nickel and iron are also added, as they differently affect alloy characteristics such as strength, ductility, and corrosion resistance. The phase transformations of nickel aluminum–bronze alloys have been the subject of many studies due to the formations of intermetallics promoted by slow cooling. In the present investigation, quaternary systems of aluminum bronze alloys, specifically Cu–10wt%Al–5wt%Ni–5wt%Fe (hypoeutectoid bronze) and Cu–14wt%Al–5wt%Ni–5wi%Fe (hypereutectoid bronze), were directionally solidified upward under transient heat flow conditions. The experimental parameters measured included solidification thermal parameters such as the tip growth rate (VL) and cooling rate (TR), optical microscopy, scanning electron microscopy (SEM) analysis, hardness, and microhardness. We observed that the hardness and microhardness values vary according to the thermal parameters and solidification. We also observed that the Cu–14wt%Al–5wt%Ni–5wi%Fe alloy presented higher hardness values and a more refined structure than the Cu–10wt%Al–5wt%Ni–5wt%Fe alloy. SEM analysis proved the presence of specific intermetallics for each alloy.

Near-eutectic Zn-Mg alloys: Interrelations of solidification thermal parameters, microstructure length scale and tensile/corrosion properties

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.

MACHINABILITY ANALYSIS OF AN AL-1,2% Pb ALLOY SOLIDIFIED IN A HORIZONTAL DIRECTIONAL DEVICE

In general, the binary monotectic alloys are characterized by the limited solubility in the liquid state, which gives them a benefited tribological behavior such as wear resistance. Researches regarding the development of monotectic alloy microstructures during the unsteady-state heat flow conditions are fundamental, as it encompasses most of the solidification industrial processes. However, the microstructural relationship between the mechanical properties of monotectic alloys is little explored and practically nil. In this context, the present study consists of investigating and correlating solidification thermal variables and structural parameters such as microhardness and machinability (cutting temperatures and tool wear) of Al-1.2wt% Pb alloy, in a horizontal directional device. It was observed that the cutting temperature and tool wear results complement each other when correlated with position and interphase spacing, indicating that for smaller interphase spacings the addition of lead harms machinability.

Correlation between microstructure, thermal parameters and mechanical properties of a directionally solidified Al-1%wt Mn alloy

This works aims to study the mechanical properties of a Al-1%wt Mn alloy directionally solidified under unsteady-state conditions. The as-cast microstructure was analysed by measuring the cellular spacing, and the mechanical properties were obtained through Vickers microhardness and tensile strength tests. The correlation between the mechanical results and the as-cast microstructure was fundamental to imply a relation between the solidification thermal parameters and the rolling process in which this kind of alloy is submitted to afterwards.

Cellular/dendritic transition, dendritic growth and microhardness in directionally solidified monophasic Sn-2%Sb alloy

Abstract Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb (mass fraction) alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate ( V L ) and the cooling rate ( T R ). High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for T R >5.0 K/s. Cellular ( l c ) and primary dendrite arm spacings ( l 1 ) are determined along the length of the directionally-solidified casting. Experimental growth laws relating l c and l 1 to V L and T R are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.