Analysis of the microstructural behavior of the Al4.5Cu5Zn semisolid alloy during partial remelting

ABSTRACT

This work aims to contribute to metal processing in the semisolid state by analyzing the microstructural behavior of the Al4.5Cu5Zn under two production routes: conventional (without a grain-refining alloy) and grain refinement. The alloy was reheated to the working temperature corresponding to a 45% solid fraction (608 °C) and maintained for various heat treatment times; the samples were then examined using metallographic techniques to evaluate their behavior. The conventionally produced alloy samples showed deficiencies in primary globule size, grain size, circularity shape factor, and rheocast quality index. Conversely, the samples produced via the grain refinement method yielded satisfactory results across all analyzed parameters, with a 55 μm reduction in average primary globule size, a 25 μm decrease in average grain size, a 0.10 increase in the circularity shape factor, and a 0.03 increase in the rheocast quality index. Additionally, the reheating treatment time influenced the results, with 60 seconds identified as the optimal duration for both production routes. This suggests that the phenomena of Ostwald ripening and coalescence primarily occur within this timeframe. Specifically, as treatment time increases, smaller dendritic arms dissolve and are incorporated into larger ones, reducing the number of dendritic arms (Ostwald ripening), while secondary dendritic arms also tend to coalesce (coalescence).

Keywords:
Thixoforming; Aluminum alloy; Al4.5Cu5Zn alloy.

1. INTRODUCTION

Aluminum, in addition to being highly abundant, is highly valued for its characteristics, including lightness, mechanical strength, corrosion resistance, thermal and electrical conductivity, and high recyclability. These qualities make it an increasingly popular choice across various industrial sectors, especially in applications that require lightweight yet strong structures. A clear example is its widespread use in the automotive and aerospace industries [¹]. The rising demand for structural efficiency in these sectors has led designers to focus on improving material performance, resulting in the development of stiffer and more durable materials [²]. The addition of alloying elements to pure aluminum improves its mechanical properties and utility, enabling the production of alloys with excellent strength-to-weight ratios. The primary alloying elements used are copper, manganese, silicon, magnesium, and zinc [³].

The semisolid metal processing has become an alternative in the industry because partially melted or solidified metals show good resistance to deformation. This occurs between the properties of metals in the solid state and those in the liquid state. This characteristic allows for improved mold filling and helps avoid common problems found in traditional metal processing methods [⁴]. Semisolid state processing is categorized into two main types: rheocasting and thixoforming. The key difference between these techniques is the physical state of the raw material. In rheocasting, the semisolid metal is created through partial solidification of the raw material, whereas in thixoforming, it is produced by partial melting [⁵,⁶,⁷,⁸]. For effective processing, the semisolid metal should contain globular solid particles evenly distributed within a liquid matrix, have a wide solidification range, and display low sensitivity of the liquid fraction to temperature changes. These parameters are crucial for proper control of the process [⁹]. Recent research shows excellent results using these methods in various aluminum alloys, especially with thixoforming. It results in globular, refined microstructures and uniform distribution of primary globules, which is an improvement over traditional casting processes that produce dendritic microstructures. These microstructural changes significantly enhance the mechanical properties of the materials. Additionally, when T5 and T6 heat treatments are applied, there is a notable increase in mechanical performance [¹⁰,¹¹,¹²].

Various semisolid processing methods have been used over the years, utilizing chemical and physical agents such as: (a) grain refinement – nucleating agents, mainly the AlTiB alloy, involve adding a substance to the liquid metal to encourage or initiate the formation of nucleation sites [¹³], (b) mechanical stirring – using horizontal or vertical rotors like blades or gear wheels, which create turbulence, causing relative movement between dendrites and the surrounding liquid to facilitate crystal multiplication [¹⁴], (c) electromagnetic stirring – applied to the solidifying liquid through strong electromagnetic fields, where the induced electric currents promote agitation, break the structure in formation, stimulate crystal multiplication, and encourage globularization [¹⁵], (d) equal channel angular pressing (ECAP) – imposes large deformations via a matrix with channels of the same cross section meeting at angles of 90° or 120°, deforming the material by simple shear [¹⁶], and (e) ultrasonic melt treatment – uses acoustic waves in the 17 to 20 kHz range on molten metal to cause cavitations and promote mixing [¹⁷].

The most commonly used alloys in semisolid processing are the commercial aluminum alloys A356, 357, 319, 355, and A390, because they show a low coefficient of thermal expansion, good mechanical strength, and corrosion resistance [⁶]. A challenge to address is the need to expand the variety of alloys used in semisolid processing. The Thixoforming research group at UNICAMP has developed and continues to develop several new alloys over the years, specifically the Al-Si-(Cu, Mg, Zn) and Al-Ti-(Cu, Mg, Zn, Si) systems, to evaluate their thixoformability. This assessment primarily involves the microstructural study of these alloys in the semisolid state, focusing on the achievement of a non-dendritic morphology. The Al-Cu-Zn system, specifically the Al4.5Cu5Zn alloy, is the basis of this study, which aims to evaluate the alloy as a raw material for thixoforming processes, analyzing its microstructural behavior.

2. MATERIALS AND METHODS

This chapter presents the methodology adopted for the development of this work, namely, raw material production, thermal characterization via Thermo-Calc® software simulations, and characterization of morphological behavior for different heat treatment time conditions. For the Al4.5Cu5Zn alloy production, commercial aluminum-copper alloy AA2024 was used with a 5 wt% zinc addition in its composition, applied through two production routes. The alloy was chosen for its high mechanical strength and favorable strength-to-weight ratio compared to other alloys, making it widely used in aerospace components.

The incorporation of zinc into the AA2024 alloy transforms the material into an Al-Cu-Zn ternary system, consequently altering its solidification path. This addition results in a depression of the liquidus temperature, attributed to the lower melting point of zinc relative to aluminum and copper. Furthermore, an expansion of the solidification interval (the range between the liquidus and solidus temperatures) is observed, a critical parameter for processing materials in the semisolid state [¹⁸]. Significant structural modifications also occur within the alloy, including the suppression of dendritic morphology and the promotion of a non-dendritic Alα phase during heating [¹⁹]. Within the eutectic constituent, zinc incorporation is evident; specifically, the grain boundaries exhibit a complex microstructural evolution that transcends standard CuAl₂ lamellae, manifesting as a Zn-enriched phase distribution.

The alloy was produced in the Thixoforming laboratory of UNICAMP. The conventional production of the alloy without the grain-refining alloy proceeded as follows: the AA2024 alloy was heated to 750 °C for complete melting in a SiC crucible (1011 grams) the commercial pure zinc (51 grams) was added. The mixture was held for about 10 minutes and stirred periodically to promote dissolution and homogenization of the molten alloy. Afterward, the material was cast into cylindrical ingot molds made of AISI 1045 carbon steel, with the inner walls coated in a thin layer of alumina aqueous solution to help with demolding the solidified ingots.

The grain refinement process followed the same procedure; however, the grain refiner alloy Al5Ti1B (40 grams) was added to achieve a non-dendritic microstructure. Using inoculant agents to refine grain structures is one of the most popular and effective methods in the industry because it is easy to apply, low-cost, and produces satisfactory results in obtaining globular microstructures while enhancing mechanical properties [², ²⁰]. Therefore, the TiB₂ (titanium diboride) particles in the Al5Ti1B grain refining master alloy are generally considered effective after reheating aluminum alloys to the semisolid state, playing a key role in microstructure stability. The TiB₂ compound has good thermodynamic stability and a high melting point, making it resistant to dissolving at typical reheating temperatures for semisolid processing. It acts as a nucleating agent during initial solidification, and even after prolonged reheating in the semisolid state, it is crucial for achieving and maintaining a non-dendritic microstructure. This is vital for semisolid processing, as sphericity ensures good thixotropy (flowability under shear) of the semisolid paste [²¹, ²²].

For each production technique, two ingots were produced, each measuring 250 mm in length and 30 mm in diameter. The chemical composition of the alloy (in wt%) is shown in Table 1 and was obtained via optical emission spectrometry.

Table 1
Chemical composition of the Al4.5Cu5Zn alloy (in wt%) as determined by optical emission spectrometry.

Cu	Zn	Mg	Mn	Fe	Si	Ti	Cr	Al
4.48	5.13	1.62	0.67	0.24	0.09	0.12	0.02	Bal.

The thermal characterization of the alloy was conducted using Thermo-Calc^® software simulations (TTAl8 database). In this simulation, the software employed calculation routines based on the lever rule and Scheil models to assess solidification conditions under both equilibrium and non-equilibrium states; this technique is chosen for its ability to predict phase stability and the chemical composition of the alloy at different temperatures. Figure 1 displays the solid fraction versus temperature, identifying the solidus temperature at 460 °C, the liquidus temperature at 628 °C, and the working temperature at 608 °C (the temperature corresponding to a solid fraction of 45%); the semisolid processing should be performed between the solidus and liquidus temperatures to achieve a non-dendritic microstructure.

Figure 1
Solid fraction versus temperature for the Al4.5Cu5Zn alloy obtained via Thermo-Calc® software simulations.

The selection of a 45% solid fraction in alloy processing is due to the ease of mold filling while maintaining the final quality of the part. This condition enables the material to exhibit thixotropy, meaning it behaves like a solid when stationary but flows like a viscous liquid when subjected to shear stress. Unlike molten metal in a fully liquid state, whose low viscosity favors turbulent flow regimes and the entrapment of air and gases, the semisolid alloy has a viscosity high enough to maintain continuous laminar flow. Finally, the reduction in processing temperature mitigates the thermal gradient at the metal-mold interface, resulting in increased mold lifespan and reducing the effects of erosion, thermal shock, and thermal fatigue of the tooling.

The alloy was reheated and held at that temperature for heat treatment periods of 0 s, 30 s, 60 s, and 90 s, and then water-cooled to samples measuring 25 mm in height and 30 mm in diameter and featuring a 3 mm diameter orifice at mid-height for the insertion of a type K thermocouple into its interior. This was done for approximately 6 minutes in a Norax induction furnace (25 kW, 8 kHz) with a heating rate of 100 °C/min in the Thixoforming laboratory of UNICAMP; it should be noted that reheating time of 0 s corresponds to the moment the sample attains the working temperature. The heat treatment (isothermal treatment) must be sufficiently long to develop a non-dendritic structure while preventing excessive grain growth that could weaken the mechanical properties of thixoforged components. Additionally, precise control is essential to ensure uniform temperature distribution within the raw material, promoting a homogeneous liquid fraction distribution. Therefore, the reheating stage must be optimized to produce semisolid material with characteristics suitable for thixoforming [²³, ²⁴].

The microstructural characterization of the alloy was conducted at the Materials characterization laboratory of UNICAMP. Two types of metallographic analyses were used: conventional metallography (B&W) the samples were ground, polished, and subjected to chemical etching with modified Keller’s reagent (1.0 ml HF, 2.5 ml HCl, 1.5 ml HNO₃, and 95.0 ml H₂O), with full immersion of the sample for approximately 10 s, followed by rinsing with running water and drying using an electric blower; and colored metallography, the same samples underwent electrolytic etching with deposition of HBF₄ (fluoboric acid) in a 1.8% solution at 40 V for 270 s under moderate and constant agitation, using a Leica DM ILM optical microscope for image acquisition. Measurements of primary globule and grain sizes were obtained by the Heyn Intercept Method, governed by ASTM E112 [²⁵]. In this method, measurements were performed in five different fields of each micrograph, and for each sample, five images from different sections were used, totaling twenty-five measurements per sample. The circularity shape factor was calculated using the free software ImageJ, and the rheocast quality index (RQI) was determined by the equation RQI = (primary globule size / grain size) * circularity shape factor. The RQI assesses the efficiency of the method for obtaining the raw material, indicating how it relates the primary globule size to the grain size. A value closer to “1” signifies that the primary globule size is similar to the grain size, resulting in a less complex structure.

It should be noted that three samples were taken from the ingot in the as-cast condition, specifically from the base, center, and top along its longitudinal direction to verify the material’s microstructural homogeneity, as carried out in previous work [²⁶]. Since the as-cast condition exhibited microstructural homogeneity, only one sample was used for the remaining conditions.

3. RESULTS AND DISCUSSION

The characterization of the alloy microstructural behavior involves analyzing its microstructure both in the as-cast state and after heat treatment at a 45% solid fraction, across different heat treatment durations. This includes measuring the sizes of primary globules and grains, determining the circularity shape factor, and calculating the RQI.

Figures 2 and 3 display the microstructures in the as-cast and 45% solid fraction at heat treatment conditions using two characterization techniques: conventional metallography (Figures 2(a) and 2(f)) and color metallography (Figures 3(a) and 3(f)). The alloy produced by the conventional method (without the grain-refining alloy) shows a fully dendritic microstructure; in contrast, the grain-refined alloy exhibits a more refined and uniform dendritic microstructure. This microstructural change indicates that the Al5Ti1B grain refiner, added during melting, tends to promote alloy refinement. Grain refinement alters the grain structure to enhance both strength and ductility in metals, achieved through processes like severe plastic deformation, rapid solidification, and inoculant addition; thus, it is a key technique in aluminum processing [²]. It is also worth noting that the high standard deviation values for the conventional route (without the grain-refining alloy) are typical in casting alloys, where significant heterogeneity exists among particles. Additionally, as seen in Figure 2(a), measuring primary globules using conventional metallography is difficult because accurately locating grain boundary regions or distinguishing whether neighboring entities separated by the eutectic are separate globules or dendritic arms of the same globule is challenging.

Figure 2
Microstructure of the Al4.5Cu5Zn alloy via conventional metallography: conventional production (a–e) and via grain refinement production (f–j) for the as-cast condition and 45% solid fraction at heat treatment times of 0 s, 30 s, 60 s, and 90 s.

Figure 3
Microstructure of the Al4.5Cu5Zn alloy via color metallography: conventional production (a–e) and via grain refinement production (f–j) for the as-cast condition and 45% solid fraction at heat treatment times of 0 s, 30 s, 60 s, and 90 s.

A matrix of the Alα phase (light gray color) and a eutectic phase present at the grain boundaries (black color) are observed in all the microstructures of Figure 2. For the conventionally produced alloy (Figures 2(b–e)), the microstructure evolves from a coarse rosette-shaped morphology at 0 s to a homogeneous, fine rosette shape at 60 s, before reverting to a coarse rosette shape at 90 s. In contrast, the fine-grained alloy (Figures 2(g–j)) exhibits a fine rosette structure tending towards a near-globular microstructure, with a slight increase in the size of the primary globules throughout the morphological evolution up to 90 s, attributed to Ostwald ripening and coalescence, both processes dependent on the alloy’s residence time at the heat treatment temperature.

Ostwald ripening and coalescence are mechanisms that involve thickening of dendritic arms, specifically the disappearance of secondary dendritic branches and the thickening of primary arms, which collectively drive globularization. These phenomena occur early in solidification when diffusion distances are minimal. Ostwald ripening involves the dissolution of smaller arms, solute diffusion through the liquid between arms, and solute incorporation into coarser arms, leading to a reduction in the number of dendritic branches and increased spacing between them. Conversely, coalescence entails the agglomeration of secondary dendritic branches, resulting in the suppression of separating interfaces and the merging of two or more branches into a larger one [²⁷].

Figure 3 shows the alloy microstructures obtained by color metallography, both for conventional production (Figures 3(b–e)) and for grain refinement conditions (Figures 3(g–j)). The conventionally produced alloy exhibits coarse rosette-shaped grains. The grain-refined alloy exhibits near-globular grains from 0 s, reaching the ideal morphology at 60 s due to Ostwald ripening and coalescence – two time-dependent processes that occur during the semisolid temperature; it is observed that, from a treatment time of 60 s, the grains begin to appear larger due to excessive permanence during the semisolid temperature, regardless of the production route.

Figure 4 shows a summary of all microstructures, namely, in Figure 4(a) a fully dendritic structure produced by the conventional method (without the grain refinement alloy), in Figure 4(b) a rosette-shaped structure (intermediate form between dendritic and globular structure) for the alloy produced by the conventional method with 45% solid fraction and a heat treatment time of 60 s, and in Figure 4(c) a near-globular structure produced via grain refinement with 45% solid fraction and a heat treatment time of 60 s.

Figure 4
Microstructure of the Al4.5Cu5Zn alloy via conventional metallography: dendritic structure (a), rosette-like structure (b), and near-globular structure (c).

Table 2 summarizes all analyzed microstructural parameters; conventional production (without a grain-refining alloy) does not yield satisfactory results compared to grain refinement methods. The as-cast condition, it is observed that the average primary globule size drops from 198 µm (conventional production) to 103 µm (grain refinement production), showing a reduction of 95 µm. The same occurs for the average grain size, where the grain size is reduced from 210 µm (conventional production) to 133 µm (grain refinement production), showing a reduction of 77 µm. When reheating heat treatment is applied, the smallest primary globule size (94 µm) and grain size (119 µm) are obtained at a 60 s heat treatment duration. However, at 90 s, there is an abrupt increase in primary globule size (206 µm) and grain size (211 µm), even surpassing the as-cast condition. The circularity shape factor (0.29) and RQI (0.23) also reach their maximum values at 60 s. Notably, the smallest primary globule size (84 µm) and grain size (102 µm) are achieved with 60 s of heat treatment, with the circularity shape factor (0.37) and RQI (0.30) being consistently higher than in conventional methods, reaching their peak at 60 s.

Table 2
Values of primary globule size, grain size, circularity shape factor, and RQI for each test condition.

CONDITION	TREATMENT TIME (s)	GLOBULE SIZE (μm)	GRAIN SIZE (μm)	CIRCULARITY (DIMENSIONLESS)	RQI (DIMENSIONLESS)
Conventional production	as-cast	198 ± 16	210 ± 17	0.11 ± 0.09	0.10 ± 0.10
	0	156 ± 9	158 ± 8	0.21 ± 0.06	0.20 ± 0.12
	30	132 ± 3	159 ± 6	0.26 ± 0.06	0.21 ± 0.14
	60	94 ± 5	119 ± 3	0.29 ± 0.04	0.23 ± 0.11
	90	206 ± 3	211 ± 3	0.24 ± 0.08	0.23 ± 0.14
Grain refinement production	as-cast	103 ± 3	133 ± 3	0.18 ± 0.04	0.14 ± 0.09
	0	89 ± 6	127 ± 4	0.31 ± 0.12	0.21 ± 0.11
	30	93 ± 2	140 ± 3	0.33 ± 0.11	0.22 ± 0.11
	60	84 ± 2	102 ± 2	0.37 ± 0.14	0.30 ± 0.15
	90	107 ± 4	172 ± 6	0.37 ± 0.18	0.23 ± 0.14

It is observed that a reheating time of 0 s for both processing techniques results in primary globules with a reduced circularity shape factor, attributed to insufficient time for coalescence and globularization processes. Conversely, increasing the isothermal holding time intensifies these mechanisms, leading to a progressive spheroidization of the microstructure [²⁸, ²⁹].

Therefore, there is an improvement (reduction) of 55 µm in the average primary globule size and 25 µm in the average grain size, that is, the difference between the primary globule and grain sizes of conventional production and grain refinement production over all the analyzed heat treatment times.These results suggest that using the Al5Ti1B grain refiner alloy in combination with the reheating heat treatment time increases the sphericity of the microstructure, highlighting Ostwald ripening and coalescence mechanisms. It is also observed that the optimal heat treatment time is 60 s, as reported by TORRES et al. [³⁰] in a recent study. Results for grain refinement are more consistent and favorable, indicating the alloy can be used in thixoforming processes.

LEOPOLDO et al. [²⁹] investigated of the Al-4.5Cu-0.5Cr semisolid alloy under varying mechanical stirring times, achieving a non-dendritic structure. For the longest stirring duration, the average primary globule size was 106 µm and a circularity shape factor of 0.51. As shown in Table 2, the grain refinement technique yields primary globule sizes comparable to those reported in the aforementioned study, while offering significantly greater operational simplicity compared to mechanical stirring.

Aluminum alloys have long been widely utilized in semisolid metal processing, and in recent years, they have gained significant attention for additive manufacturing applications. However, the current selection of aluminum alloys suitable for additive manufacturing remains limited, as many are susceptible to defects such as porosity, hot cracking, and surface roughness, which compromise high-performance applications. Nevertheless, the addition of Ni to Al-Cu system alloys is enhancing mechanical properties at elevated temperatures and promoting a narrower solidification range. This results in a reduction of hot cracking and porosity in the final product, thereby expanding the application field of these alloys [³¹].

4. CONCLUSIONS

This study investigated the Al4.5Cu5Zn alloy, produced through two different methods. It was then reheated to its semisolid temperature for various heat treatment durations to analyze its microstructural behavior, resulting in the following conclusions:

• The results showed that there is an reduction of 55 µm in the average primary globule size and 25 µm in the average grain size, that is, the difference between the primary globule and grain sizes of conventional production and grain refinement production over all the analyzed heat treatment times.

• The optimal reheating treatment time was 60 s for both production routes, indicating that Ostwald ripening and coalescence mainly occur within this period. As the treatment time increases, smaller dendritic arms dissolve and are incorporated into larger ones, leading to a decrease in the number of dendritic arms (Ostwald ripening) and the agglomeration of secondary dendritic arms (coalescence).

Therefore, the grain refinement route is a straightforward, low-cost, and effective method for producing stable, non-dendritic microstructures suitable for semisolid processing of the Al4.5Cu5Zn alloy, enhancing its potential for use in structural components for the aerospace and automotive industries.

5. ACKNOWLEDGMENTS

The authors would like to thank FAPESP (State of São Paulo Research Foundation – Project 2022/05050-5 and 2024/06996-6), CNPq (National Council for Scientific and Technological Development – Project PQ 303299/2021-5), FEM/UNICAMP (Faculty of Mechanical Engineering, Campinas State University), and IFSP (São Paulo Federal Institute of Education, Science, and Technology) Bragança Paulista and Sorocaba campuses for providing financial support.

6. DATA AVAILABILITY

All the data supporting the results of this study were published in the article itself.

7. BIBLIOGRAPHY

• ^[1] OLIVEIRA, J.A.M.M., “Caracterização microestrutural de ligas eutéticas de alumínio no estado bruto de fusão e tratadas termicamente por homogeneização”, M.Sc. Thesis, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, 2017.
• ^[2] TAJUDIN, M.F.M., AHMAD, A.H., ALIAS, J., et al., “Grain refinement in semisolid metal processing: current status and recent development”, International Journal of Advanced Manufacturing Technology, v. 124, n. 5-6, pp. 1379–1399, 2023. doi: https://doi.org/10.1007/s00170-022-10590-9.
  » https://doi.org/10.1007/s00170-022-10590-9
• ^[3] BUGARIN, A.F.S., “Estudo da resistência à corrosão das ligas de alumínio 2024-T3 e 7475-T651 soldadas por fricção e mistura (FSW)”, M.Sc. Thesis, Instituto de Pesquisas Energéticas e Nucleares, Universidade de São Paulo, São Paulo, São Paulo, 2017.
• ^[4] FAN, Z., “Semisolid metal processing”, International Materials Reviews, v. 42, n. 2, pp. 49–85, 2002. doi: https://doi.org/10.1179/095066001225001076.
  » https://doi.org/10.1179/095066001225001076
• ^[5] KAPRANOS, P., “Semisolid metal processing – a process looking for a market”, Diffusion and Defect Data, Solid State Data. Part B, Solid State Phenomena, v. 141-143, pp. 1–8, 2008. doi: https://doi.org/10.4028/www.scientific.net/SSP.141-143.1.
  » https://doi.org/10.4028/www.scientific.net/SSP.141-143.1
• ^[6] FLEMINGS, M.C., “Semisolid forming: the process and the path forward”, Metallurgical Science and Tecnology, v. 18, n. 2, pp. 3–4, 2013.
• ^[7] YOUNG, K., EISEN, P., “SSM (semisolid metal) technological alternatives for different application”, Metallurgical Science and Tecnology, v. 18, n. 2, pp. 11–15, 2013.
• ^[8] FREITAS, C.C., “Processamento semissólido de ligas de alta entropia: microestrutura, morfologia, reologia e comportamento mecânico de ligas do sistema CoCrCuFeNi”, D.Sc. Thesis, Universidade Estadual de Campinas, Campinas, São Paulo, 2021.
• ^[9] LIU, D., ATKINSON, H.V., JONES, H., “Thermodynamic prediction of thixoformability in alloys based on the Al-Si-Cu and Al-Si-Cu-Mg systems”, Acta Materialia, v. 53, n. 14, pp. 3807–3819, 2005. doi: https://doi.org/10.1016/j.actamat.2005.04.028.
  » https://doi.org/10.1016/j.actamat.2005.04.028
• ^[10] SAMAT, S., OMAR, M.Z., BAGHDADI, A.H., et al., “Mechanical properties and microstructures of a modified Al-Si-Cu alloy prepared by thixoforming process for automotive connecting rods”, Journal of Materials Research and Technology, v. 10, pp. 1086–1102, 2021. doi: https://doi.org/10.1016/j.jmrt.2020.12.085.
  » https://doi.org/10.1016/j.jmrt.2020.12.085
• ^[11] AZIZ, A.M., OMAR, M.Z., SAMAT, S., et al., “Microstructural and tensile behavior of a thixoformed Al-Si-Cu-Mg given T5 and T6 heat treatments tested at room and elevated temperatures”, International Journal of Metalcasting, v. 18, n. 3, pp. 2343–2356, 2024. doi: https://doi.org/10.1007/s40962-023-01155-x.
  » https://doi.org/10.1007/s40962-023-01155-x
• ^[12] SAMAT, S., OMAR, M.Z., MOHAMED, I.F., et al., “A comparative study on microstructure, mechanical property and damping capacity of hypoeutectic Al-Si-Cu alloy for different casting Technologies”, International Journal of Metalcasting, v. 19, n. 2, pp. 1180–1193, 2025. doi: https://doi.org/10.1007/s40962-024-01376-8.
  » https://doi.org/10.1007/s40962-024-01376-8
• ^[13] KEARNS, M.A., THISTLETHWAITE, S.R., COOPER, P.S., “Recent advances in understanding the mechanism of aluminium grain refinement by TiBAl master alloys”, In: 125th The Minerals, Metals and Materials Society Annual Meeting, Anaheim, USA, 1996.
• ^[14] PRONI, C.T.W., “Efeito da taxa de aquecimento no desmantelamento e na globularização da microestrutura para propiciar a tixoconformação”, D.Sc. Thesis, Universidade Estadual de Campinas, Campinas, São Paulo, 2014.
• ^[15] VIVÉS, C., “Elaboration of semisolid alloys by means of new eletromagnetic rheocasting processes”, Metallurgical Transactions. B, Process Metallurgy, v. 23, n. 2, pp. 189–206, 1992. doi: https://doi.org/10.1007/BF02651854.
  » https://doi.org/10.1007/BF02651854
• ^[16] SEGAL, V.M., “Materials processing by simple shear”, Materials Science and Engineering A, v. 197, n. 2, pp. 157–164, 1995. doi: https://doi.org/10.1016/0921-5093(95)09705-8.
  » https://doi.org/10.1016/0921-5093(95)09705-8
• ^[17] ZHANG, L., ESKIN, D.G., KATGERMAN, L., “Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys”, Journal of Materials Science, v. 46, n. 15, pp. 5252–5259, 2011. doi: https://doi.org/10.1007/s10853-011-5463-2. PubMed PMID: 36039104.
  » https://doi.org/10.1007/s10853-011-5463-2
• ^[18] DANTAS, A.V.R., BROLLO, G.L., TAMAYO, D.V., et al., “Thixoforming of an Al-Si-Zn-Mg Alloy – Thermodynamic characterization, microstructural evolution and rheological behavior”, Materials Research, v. 24, n. 2, pp. e20200313, 2021. doi: https://doi.org/10.1590/1980-5373-mr-2020-0313.
  » https://doi.org/10.1590/1980-5373-mr-2020-0313
• ^[19] TAMAYO, D.V., BROLLO, G.L., DE OLIVEIRA, J.R., et al., “The thixoforming process window for Al-Si-Zn alloys using the differentiation method: the role of Si, heating rate and sample mass”, Metals, v. 12, n. 5, pp. 734, 2022. doi: https://doi.org/10.3390/met12050734.
  » https://doi.org/10.3390/met12050734
• ^[20] AL-QAWABAH, S.M.A., ZAID, A.I.O., “Effect of Mo addition to ZA22 alloy grain refined by Ti-B on its metallurgical and mechanical characteristics in the as cast condition”, Materials Science Forum, v. 886, pp. 64–68, 2017. doi: https://doi.org/10.4028/www.scientific.net/MSF.886.64.
  » https://doi.org/10.4028/www.scientific.net/MSF.886.64
• ^[21] CIBULA, A., “The mechanism of grain refinement of sand casting in aluminium alloys”, Journal of the Institute of Metals, v. 76, pp. 323–360, 1949.
• ^[22] JONES, G.P., PEARSON, J., “Factors affecting the grain-refinement of aluminum using titanium and boron additives”, Metallurgical Transactions. B, Process Metallurgy, v. 7, n. 2, pp. 223–234, 1976. doi: https://doi.org/10.1007/BF02654921.
  » https://doi.org/10.1007/BF02654921
• ^[23] HIRT, G., KOPP, R., Thixoforming: semi-solid metal processing, Weinheim, John Wiley & Sons, 2009. doi: https://doi.org/10.1002/9783527623969.
  » https://doi.org/10.1002/9783527623969
• ^[24] KIRKWOOD, D.H., SUÉRY, M., KAPRANOS, P., et al., Semisolid processing of alloys, Berlin, Springer, 2010. doi: https://doi.org/10.1007/978-3-642-00706-4.
  » https://doi.org/10.1007/978-3-642-00706-4
• ^[25] AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM E112: Standard test methods for determining average grain size, West Conshohocken, ASTM, 1996.
• ^[26] [26] TORRES, L. V., ZOQUI, E. J., “Otimização do processamento da matéria-prima semissólida AA356”, Tecnologia em Metalurgia, Materiais e Mineração, v. 18, pp. e2227, 2021. doi: https://doi.org/10.4322/2176-1523.20212227.
  » https://doi.org/10.4322/2176-1523.20212227
• ^[27] BENATI, D.M., “Avaliação da tixoconformabilidade de ligas Al-Xwt%Si-2,5wt%Cu-0,5wt%Mg”, M.Sc. Thesis, Universidade Estadual de Campinas, Campinas, São Paulo, 2008.
• ^[28] POLA, A., TOCCI, M., KAPRANOS, P., “Microstructure and properties of semi-solid aluminum alloys: a literature review”, Metals, v. 8, n. 3, pp. 181, 2018. doi: https://doi.org/10.3390/met8030181.
  » https://doi.org/10.3390/met8030181
• ^[29] LEOPOLDO, R.M., ZIMPEL, I., BARCELLOS, V.K., et al., “Processamento no estado semissólido e caracterização microestrutural e mecânica da liga de alumínio Al-4,5Cu-0,5Cr”, Observatorio de la Economía Latinoamericana, v. 23, n. e10104, pp. e10104, 2025. doi: https://doi.org/10.55905/oelv23n5-183.
  » https://doi.org/10.55905/oelv23n5-183
• ^[30] TORRES, L.V., PASCHOAL, J.P.O., LOURENÇATO, L.A., et al., “The influence of ultrasonic melt treatment on microstructural evaluation of the Al7Si2.5Cu alloy for semisolid processing”, Materials Research, v. 27, pp. e20240314, pp. e20240314, 2024. doi: https://doi.org/10.1590/1980-5373-mr-2024-0314.
  » https://doi.org/10.1590/1980-5373-mr-2024-0314
• ^[31] SCHON, A.F., “Avaliação das ligas Al-5%Cu e Al-4%Cu-1%Ni tratadas por refusão à laser para aplicação em manufatura aditiva”, M.Sc. Thesis, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, 2022.

Publication Dates

• Publication in this collection
  20 July 2026
• Date of issue
  2026

History

• Received
  03 Feb 2026
• Accepted
  03 June 2026