INFLUENCE OF SQUEEZE CASTING PROCESS IN THE MECHANICAL PROPERTIES OF Cu-Al-Be SHAPE MEMORY ALLOY

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1 INFLUENCE OF SQUEEZE CASTING PROCESS IN THE MECHANICAL PROPERTIES OF Cu-Al-Be SHAPE MEMORY ALLOY IEVERTON CAIANDRE ANDRADE BRITO, 1 FRANCISCO WLAUDY ERIMAR LOURENÇO DE ARAÚJO JÚNIOR, 1 RAFAEL EVARISTO CALUÊTE, 1 THAYZA PACHECO DOS SANTOS BARROS, TADEU ANTÔNIO DE AZEVEDO MELLO, 1 1 Federal University of Paraíba (UFPB), Department of Mechanical Engineering, Rapid Solidification Laboratory, Cidade Universitária, S/N João Pessoa/PB, BRAZIL Abstract. Casting is the most feasible to transform raw materials into industrial components processing route. However, a major disadvantage present in both conventional process and the sophisticated techniques is the presence of defects such as porosities. Squeeze casting is a term generally used to represent a process in which liquid metal is cast in a permanent mold and undergoes compression until it is fully solidified. The high s applied in the process enable a reduction in the degree of microsegregation and the grain refinement, reduction of solidification shrinkage, significantly decreased porosity and increased density, resulting in parts with superior qualities to those obtained by the conventional casting procedures, in addition to combine high strength with good ductility. This study aims to assess the influence that the squeeze casting process, increase the mechanical properties, microstructure and density of the Cu-Al shape memory alloy. To do so, ingots under various processing conditions were prepared by squeeze casting process, using an electric resistance furnace without atmosphere control and a semi-automatic hydraulic press. Finally, the samples were characterized by microhardness tests, hardness, static tensile test and verification of density. It can be seen that the level of applied and heat treatments taxes, significantly interfere with the microstructure and consequently the tensile strength of the alloy studied. Keywords: squeeze casting, microstructure, porosity, shape memory alloy 1. INTRODUCTION It is known that the casting process is the most economical route to transform raw materials into industrial components. However, one of the greatest disadvantages in the conventional processes and in the most sophisticated techniques is the presence of defects caused by the segregation and porosity that may be potential initiators of cracks when the service components are products in their raw state fusion (Ghomashchi et al., 2000). Therefore, many techniques have been developed in order to minimize these limitations and to optimize the mechanical properties of cast components. The squeeze casting process has been widely used in metal materials in a wide temperature range from low melting temperatures such as aluminum and zinc to high melting point metals as steel and nickel (Vijian et al., 2005). The term is generally used to represent a manufacturing process in which liquid metal is cast in a permanent mold and undergoes compression until all the metal is fully solidified mass (Hajjari et al., 2008). This is a hybrid process that combines the features inherent to casting and forging processes all in one by means of a hydrostatic press (Vijian et al., 2005), resulting in considerable cutback of energy (Ghomashchi et al., 2000). In the literature many names are adopted for this process, some of them are: liquid metal forging, crystallization (Hajjari et al., 2008) extrusion casting (Yang, 2003), however, this is the same process. One of the main reasons for the interest in the squeeze casting process is partly because of the elements produced by this method take mechanical properties far superior to those obtained by conventional casting and very similar to the properties of the components obtained by forging (Sukumaran et al., 2008). Thus, the method provides high productivity and excellent medium for more ways to approximate its final geometry (Zhang et al., 2008), there is the possibility of manufacturing parts with complex shapes with thin walls and holes (Ghomashchi et al., 2000) and with minimum cost (Bhagat, 1988). Thus, the process further allows obtaining a refined microstructure, concomitantly with the reduction or elimination of shrinkage defects (Zhang et al., 2008) and porosities. The various studies in the literature show the effectiveness of the squeeze casting process in increasing the mechanical strength of alloys processed by this technique. Thus, the objective of this study is to evaluate the effect that the application temperature for the same pouring temperature would bring the mechanical properties of the alloy with shape memory effect CuAlBe with presence of Nb as grain refiner. The shape memory effect is present in a set of materials or alloys capable of undergoing a reversible martensitic transformation. It is, therefore, the ability these materials have to recover a predefined geometry when subjected to an appropriate thermomechanical cycle. This reversible martensitic transformation is the driving force for this phenomenon and generates, contrary to what occurs in

2 the steel, a martensitic phase, which has hardness lower than the austenitic phase which may occur by: changes in temperature or tension application (Funakubo, 1987). 2. METHODOLOGY 2.1. Materials The material used in this work was the alloy with nominal composition Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (mass fraction). The alloy was mechanically wherein after applying heat treatment quenching from 1123K stirred and cooled in water at 298K Casting Method The alloy was melted in a muffle furnace of JUNG and without atmosphere control. The adopted pouring temperature was 1423K to overheating of the order of 403K and the cast material in a metal mold suitably made of SAE 1045 steel, as shown in Fig. 1. s of 30, 60, 90 and 120MPa imposed to the material from the liquid state until its complete solidification were obtained by means of a semiautomatic hydraulic press with capacity of 40 tonnes. a b c Figure 1. Top view of the metal mold with the pouring channel (a) side view of the punch used for the compression of the liquid metal (b) and punch assembly/cast coupled (c) 2.3. Samples After application of the shaped squeeze casting process under various s, ingots were homogenized at ambient atmosphere for 12 hours at 1123 K and then machined by a wire electro erosion process in the manner indicated in Fig. 2. The Parts a and b of Fig. 2 indicate the parts to be used for the static tensile tests (a) and micro/macrohardness analysis, micro/macrographs and measurement of the density (b) respectively. a b Figure 2. Ingot machined by electro erosion process the wire indicating the parts to be used for the static tensile tests (a) and the hardness analysis, metallography and quantification of density (b) 2.4. Metalographic Analysis Samples for metallographic observation were wet sanded and polished with alumina (1μm) and then etched with a solution of 10% (in volume) of ferric chloride in water. For the microstructural observation was used equipment brand Karl Zeiss, model Axiotech 100 (Iowa, USA), connected directly to a computer. While macrographic analyzes were performed using a scanner hp brand, model number 4000.

3 2.5. Microhardness Analysis For microhardness tests, we used a Shimadzu micro hardness tester HMV, applying load of 4.9N for a period of 15 seconds. The indentations were made on vertical and horizontal center lines of samples and 1mm spacing Hardness Analysis As for the hardness tests, we used a tester Panambra Pantec model, applying load and 600N diamond indenter with a cone type 120, corresponding to the Rockwell Hardness (Rockweel A) Density Measurement The density of the samples was calculated using Archimedes's principle. For the determination of the mass of the submerged sample was made using a specific device at a scale model of BK500 GEHAKA Tensile Test The static tensile tests were carried out using a Servo Pulser EHF Shimadzu machine with a 50KN load cell and heating and cooling chamber. The deformation rate used in this paper was 0.5 mm/min. The dimensions of the test specimen and its schematic representation are given in Tab. 1 and Fig. 3 respectively. Table 1. Specimen Dimensions adopted in this work (dimension in mm). A B C D R RESULTS AND DISCUSSION 3.1. Macrographic Analysis Figure 3. Representation of the specimen used for static tensile testing Through Figure 4, we can see that the leaked sample without application results in the presence of shrinkage defect and columnar grains located in the regions in contact with the metal mold, and the presence of such grains cannot be verified in the upper region of the ingot, i.e. in the region in contact with the atmospheric air and hence at lower cooling rates. The equiaxed grains appears in a raw and non-uniform morphology to the condition of no. For the s of 60, 90 and 120MPa we did not notice the presence of shrinkage defects on the top of the ingots. The alloy solidified to 30MPa, compared with the sample solidified without, presented a more refined microstructure. We could notice the presence of finer columnar grains in the parts in contact with the mold and a chill zone in contact with the punch. For the condition of 60MPa, grains still present with fine morphology, similar to the solidified alloy to 30MPa and conventionally processed. Observing in detail the macrostructures of the solidified alloys from 90MPa, one can notice the lack of columnar regions throughout the ingot. Thus, we can state, that for the s used in this paper to 90MPa is the minimum required to eliminate the columnar regions. When it comes to the alloy squeezed to 120MPa did not show columnar regions, but it presented a more refined macrostructure and apparently more uniform.

4 Figure 4. Macrography of the alloy s ingots with composition of Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (wt.%), 1423 K castings without the application of (a) 30MPa (b) 60MPa (c) 90MPa (d) and 120MPa (e) 3.2. Micrographic Analysis All micrographs shown in Fig. 5 were taken from the center of the samples for comparison. It can be seen that there was a small change in the morphology of the grains to the solidification conditions with increasing applied, however, the morphology of the grains appear much more uniform and finer than the grains of the solidified sample without applying. a b c d e Figure 5. Micrography of the alloy s ingots with composition of Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (wt.%), castings to 1423 K and without application of (a) 30MPa (b) 60MPa (c) 90MPa (d) and 120MPa (e)

5 3.3. Microhardness Analysis With the Table 2 you can see that there is hardly any significant variation in the hardness of the alloys solidified in atmospheric s, 30, 60 and 120MPa. For the case of the alloy solidified to 90MPa, one can notice there is a small increase in the microhardness value, and this is explained by a variation in the alloy composition, more specifically in the beryllium composition, since, as reported by Brito (2012), 0.1% beryllium in weight alters the phase transformation temperatures around 100 K. One can then say that unlike the other samples, the compressed alloy with 90MPa remains austenitic at room temperature. So, a change in the variables under study is expected since it is known that in alloys with memory effect, unlike what occurs in the steels, the austenitic phase has a higher hardness than the martensitic phase (Funakubo, 1987). Table 2. Experimental results for the Vickers microhardness the Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (wt.%) alloy. Microhardness Vickers Hardness Analysis When comparing the values of Table 2, the similarity between them is striking and you can tell that the alloy solidified with 90MPa has the highest hardness value. This is because of the unique presence of austenitic phase in the sample solidified to 90MPa as reported in section 3.3. Table 3. Experimental results for Rockwell hardness the Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (wt.%) alloy. Rockwell A hardness Density Measurement It can be seen that there is a slight variation of the density of 1423 K-Atm. alloy and the other analyzed samples. This small density variation is attributed to a small variation in composition, possibly due to the loss of aluminum remelts Tensile Tests Table 4. Experimental results for the density of Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (wt.%). Density (kg/m 3 ) 7,362 7,181 7,176 7,161 7,180 Depending on the composition of variations already mentioned in previous sections, the induction tensions of martensite have been changed. As such event prevents the comparison of the tensions and breaking deformation curve of each processing condition by the squeeze casting method, we chose to quantify only the inherent part of austenitemartensite transformation. In Figure 6, it is shown the tension versus deformation curve of a shape memory alloy with nominal composition in weight percentage Cu-11.8Al-0.6Be-0.5Nb, obtained by tensile test. As the composition of the alloy assures the presence of only the austenitic phase, the curve is characterized by a linear portion corresponding to elastic deformation of the austenite (strain ε 1 ), followed by the curve associated with the phase transformation induced tension (ε = ε 2 - ε 1 ) (Oliveira, 2009). Therefore, through this technique, it is possible to measure only the deformation referring to phase transformation and thus reduce the error caused by accommodation of claw-body test system during tractive effort, as well as dispersions in the induction tension of certain samples in greater or lesser extent.

6 Figure 6. Tension-deformation diagram representation. Indication of the value ε = ε 2 - ε 1 used as a benchmark in this work. Figure edited from the original version of OLIVEIRA (2009) According to the data contained in Tab. (5) is possible check the absence of an effective correlation between the maximum deformation of rupture and the level of applied. It can be seen that the s 30, 60 and 90MPa resulted in higher strain values compared to the conventionally cast ingot. These results are in agreement with results obtained by Boschetto et al. (2007) and Wu et al. (2010) claiming to be a direct relationship between increased rupture strain with increasing applied. Table 5. Experimental results for the maximum deformation of the Cu-11.8Al-0.58Be-0.5Nb-0.27Ni (wt.%). Average values in 10 trials. Deformation (%) 8.03 ± ± ± ± ± 0.59 Samples conformed to 30MPa and 90MPa resulted in a similar increase and around 17.68% in relation to the sample formed without. However, it is seen that the diversion of 1.1MPa to the compressed sample with 90MPa is about 2.5 times higher than the deviation of the sample compressed to 30MPa; while the sample solidified under 30MPa resulted in a deviation 2.33 times lower than the alloy conventionally shaped. Coupled with the foregoing, it can be said that the 30MPa may be considered the most suitable since it is necessary for this condition financially less expensive apparatus Defects of Casting As you can see in Fig. 7, the shaped ingot with 30MPa displayed a large shrinkage defect in the center and at approximately 2/3 of its height. The most likely cause for the occurrence of such a defect is small overheating (of the order of 403 K) used for casting ingots and low adopted, which favors the formation of a frozen layer around the mold cavity, preventing the expulsion of gases originated metal contraction during solidification. Lee et al. (2000) studied the influence of the casting temperature and the level of applied to an Al-Si alloy and found that for all casting temperatures applied there was the presence of shrinkage defects. Figure 7. Defects of casting observed after machining of ingots

7 4. CONCLUSION Given the above, we can concluded that: - The mold designed for the development of this work proved to be efficient. - The re-melts of the various ingots resulted in small changes in the nominal composition of the alloy, which resulted in changes in the present phases. - The of 30MPa allied to 1423 K pouring temperature proved to be the most viable for the maximization of the league rupture strain with nominal composition Cu-11.8Al-0.58Be-0.5Nb-0.27Ni in weight. - The density of the samples did not change significantly before the various processing conditions. - The microhardness and hardness of the samples had a small dispersion due to the applied level, the alloy being formed to 90MPa resulted in increased hardness to be fully austenitic. - The microstructure was sensitive to changes in the level of applied. - The 90MPa was assumed to be the boundary to the disappearance of the columnar grains. 5. ACKNOWLEDGEMENT The authors would like to kindly thank the Laboratory Quick Solidification of the Federal University of Paraíba (UFPB) and the Brazilian National Council for Scientific and Technological Development (CNPq). 6. REFERENCES Bhagat, R. "High squeeze casting of stainless steel wire reinforced aluminium matrix composites". Composites, v.19, n.5, p Boschetto, A., G. Costanza, et al. "Cooling rate inference in aluminum alloy squeeze casting". Materials Letters, v.61, n.14, p Brito, I. C. A. "Influência da ciclagem térmica nas temperaturas de transformação de fase e quantificação das deformações residuais em ligas com memória de forma Cu-Al-Be-Nb-Ni". Departamento de Engenharia Mecânica, Universidade Federal da Paraíba, João Pessoa, p. Dai, W., S. Wu, et al. "Effects of rheo-squeeze casting parameters on microstructure and mechanical properties of AlCuMnTi alloy". Materials Science and Engineering: A, v.538, p Funakubo, H. Shape Memory Alloys. London: Gordon and Breach Science Publishers p. Ghomashchi, M. e A. Vikhrov. "Squeeze casting: an overview". Journal of Materials Processing Technology, v.101, n.1, p Hajjari, E. e M. Divandari. "An investigation on the microstructure and tensile properties of direct squeeze cast and gravity die cast 2024 wrought Al alloy". Materials & Design, v.29, n.9, p Lee, J., C. Won, et al. "Effects of melt flow and temperature on the macro and microstructure of scroll compressor in direct squeeze casting". Materials Science and Engineering: A, v.281, n.1, p Oliveira, D. F. D. "Determinação das propriedades termomecânicas de ligas Cu-Al-Ni e Cu-Al-Be com efeito memória de forma para utilização como atuadores mecânicos". Departamento de Engenharia Mecânica, Universidade Federal da Paraíba, João Pessoa, p. Sukumaran, K., K. Ravikumar, et al. "Studies on squeeze casting of Al 2124 alloy and % SiCp metal matrix composite". Materials Science and Engineering: A, v.490, n.1, p Vijian, P. e V. Arunachalam. "Experimental study of squeeze casting of gunmetal". Journal of Materials Processing Technology, v.170, n.1, p Yang, L. "The effect of casting temperature on the properties of squeeze cast aluminium and zinc alloys". Journal of Materials Processing Technology, v.140, n.1, p Zhang, M., S. Xing, et al. "Design of process parameters for direct squeeze casting". Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, v.15, n.3, p RESPONSIBILITY NOTICE The author(s) is (are) the only responsible for the printed material included in this paper.