Comparison and Analysis on Die Casting Properties of A356 and ADC12

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1 doi: / Comparison and Analysis on Die Casting Properties of A356 and ADC12 Minying Hu*, Yongying Sang,Na Li,Bo Sun,Huali Yu,Yi Zhang,Xiaoshun Zhao College of Mechanical and Electrical Engineering, Hebei Agricultural University, Baoding , China *Corresponding author( Abstract The defects of die casting are much more in use of A356 aluminum alloy for polishing plate than ADC12 aluminum alloy. And the surface quality has not been improved using the die casting parameters optimized, filling mold is not smooth. When the parameters of ADC12 aluminum alloy are as follows, the shot pressure is100mpa, the die temperature is 260, casting temperature is 680, the shot speed is 3m/s, and the outline of castings obtained is clear, also the defects are not obvious. So ADC12 is easy forming, and matches well with mold and die casting machine. Keywords: Mechanical Properties, Microstructure, Die Casting Technology 1. INTRODUCTION In order to reduce the weight and the costs of automobiles, research and production of aluminum alloys is gaining interest rapidly in recent years (Yamada, 2002; Murakami,1999; Sakai, 2000). The commercial importance of these alloys is based on their high fluidity and low shrinkage properties in casting, brazing and welding applications. Furthermore, a high specific strength and good corrosion resistance renders these alloys suitable for manufacturing purposes; the hardness of Si particles imparts wear resistance to these alloys. It is well accepted that small additions of rare earth elements are of great importance to improve the mechanical properties of aluminum alloys and provide extended alloying capabilities. Die casting technique is widely used for fabricating the automotive components of Al and Mg alloys (Aghion, 2007). In die casting process, liquid melts are injected into die cavities at a high speed. The die casting of ADC12 alloy has been investigated by Zhao et al. (Zhao, 2009), the analyzed porosities formation in ADC12 castings with numerical simulation and experimental analysis (Khalifa, 2010; S. Janudom, 2010; Wang, 2011), and concluded that the tensile properties decreased dramatically for ADC12 die castings when porosity fraction and maximum size were more than 3.2% and 170 lm, respectively. 2. MATERIALS In this article, two kinds of aluminum alloy A356 and ADC12 were used to do die-casting experiment (Ran, 2008; Jiang, 2012; Jiang, 2013), before the experiment aluminum ingots were put in the baking furnace to remove moisture contained. The chemical composition of aluminum alloys were shown in Table 1, EXPERIMENTAL The A356 and ADC12 aluminum alloys were firstly melted in an electric resistance furnace, refined and the temperature was maintained at C. Secondly, the liquid A356 and ADC12 aluminum alloys at a given temperature were poured into a stainless steel crucible on the pouring station and stirred by a weak electromagnetic field for a short time. In the die casting process, the parameters of die casting had great influence on the mechanical properties of die castings, such as pouring temperature, shot pressure, mold temperature, shot speed, and so on. The parameters of shot pressure and mold temperature were fixed in the experiment, and it studied mainly the influence of pour temperature and shot speed on the quality and microstructure on A356 and ADC12 die casting. The parameters of experiment depended on the reference, the characteristic of alloys and the properties of die casting machine. The parameters of A356 aluminum alloy was follows: shot pressure 100Mpa, mold temperature 260, shot speed 2 m/s and 4m/s, pouring temperatures 640 and 670. The summary of the parameters used in this study was illustrated in Table

2 The parameters of ADC12 aluminum alloy was follows: shot pressure 100Mpa, mold temperature 260, shot speed 2m/s-4m/s, pouring temperatures The summary of the parameters used in this study was illustrated in Table RESULTS AND DISCUSSIONS Principle of crystallization from a metal, a metal from a liquid to process solid metal crystallization will occur, in this process first of all to produce crystal nuclei, and then grow up, the solidified metal having a certain degree of subcooling conditions to complete. Nuclei radius and surface energy and system nucleation free energy change relations can be expressed by the following formula. 2 2 T r m G L T In the formula, nuclei radius / cm; is the interface between the liquid and the surface energy of nuclei / J cm -2 ; G is crystallization process system free energy change / J cm -3 ; T m is the melting point of the alloy / K; L is crystalline potential alloy / J cm -3 ; T is subcooling / K. For certain alloys,, T m and L are constants, so the radius of the critical nucleus only has a relationship with the degree of super cooling, and inversely with the degree of super cooling. Furthermore, the relationship between the degrees of cold crystallization nucleation rate is shown in Fig.1. We can see from the figure, the degree of super cooling small, small nucleation rate, which is required, and because the nucleation power. When increasing the degree of super cooling, nucleation rate increases, but when the sub cooling is too large, the degree of diffusion of atomic drop, and the nucleation rate decreases. I Figure 1. The relation of nucleation rate and degree of super cooling In short, the alloy grain size depends on two factors, Serve the nucleation rate and growth rate. Those who can increase or decrease the nucleation rate of crystal growth rate, you can get a finer grain structure. Table1. A356 chemical composition(wt%) Si Fe Mg Mn Zn Cu Al balance Table 2. ADC12 chemical composition(wt%) Si Fe Mg Mn Zn Cu Al balance ΔT Table 3. A356 aluminum die experimental program Numbers Shot pressures(mpa) Mold temperature( ) Pouring temperature( ) Shot speed(m/s)

3 Table 4. ADC12 aluminum die experimental program Numbers Shot pressures(mpa) Mold temperature( ) Pouring temperature( ) Shot speed(m/s) Microstructure and Mechanical Properties of A356 The microstructure grinded and polished was shown in Fig.2, which of sample was obtained at the pouring temperature 670, shot speed 2m/s. The organization of A356 aluminum die casting was the primary α-al phase, and the eutectic Si phase distributed in the base metal as well as the Mg2Si strengthening phase and Fe-rich phase compounds. The primary α-al dendrites had been generated in the filling and solidification process. While α dendrite forced liquid without crystallization flow under pressure casting conditions. However, it caused collision and friction between dendrites and dendrites, dendritic and alloy liquid, furthermore α dendrite would be cut and broken corners fine dendrites and dendritic, to form dendritic rose-shaped and cellular crystals. The eutectic Si phase along the grain boundary of primary α-al phase is small flakiness and short stick. So die casting could make the grain refining. Tensile mechanical properties of the sample were shown in Table 5, under the conditions of the pouring temperature 670 and injection speed 2m/s. Figure 2. Pouring temperature of 670 and shot speed of 2m/s A356 castings microstructure Under die casting conditions, the mechanical properties of A356 aluminum alloy can be improved. Combined with microstructure analysis, more fine and uniform grain size is, better mechanical properties are. And more developed dendrites are, the worse mechanical properties perform. The mechanical properties perform better only grainy and spherical distribution appears in the eutectic Si phase. Otherwise the mechanical properties perform worse when non uniform flaky crystals appear. Eutectic Si has an isolated action on α-al matrix so that stress concentration appears in the sharp edges. And then crystalline should crack along with the boundary or needle-like eutectic Si phase would crack directly to form cracks. These reasons had a great influence on the mechanical properties of aluminum alloy A356, which had made the elongation decrease obviously Microstructure and Mechanical Properties of ADC12 As can be seen from Figures 3, 4, 5 and 6, die castings have no obvious defects at pouring temperature 700, having surfaces which are quite smooth and a clear outline than is obtained at other pouring temperatures. Microscopic pores in the castings are shown in Figure 3. The number of casting porosity is more than the one at pouring temperature 660 and 680 significantly. It has been led to increasing pouring temperature, and the molten aluminum is oxidized severely and has generated more gas which can t be discharged in time and are more along with the quicker speed. 128

4 (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 3. The surface quality of samples at different shot speeds and pouring temperature 700 Table 5. Mechanical properties of A356 aluminum alloy die castings Pouring temperature ( ) Shot speed(m/s) results σ b(mpa) δ(%) HV(0.05) (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 4. Pouring temperature of 660 different injection speed castings microscopic pores (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 5. Pouring temperature of 680 different injection speed castings microscopic pores (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 6. Microscopic pores at different shot speeds and pouring temperature

5 Revista de la Facultad de Ingeniería U.C.V., Vol. 31, N 12, pp , 2016 (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 7. Pouring temperature of 660 different injection speed castings microstructure (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 8. Pouring temperature of 680 different injection speed castings microstructure The microstructure of die casting is shown in Figures 7, 8 and 9 along with shot speeds at the condition of pouring temperature 700. And shot speeds are 2m/s, 3m/s, 4m/s respectively. (a)shot speed 2m/s (b)shot speed 3m/s (c)shot speed 4m/s Figure 9. Microstructure at different shot speeds and pouring temperature 700 Figure 9(a) for the pouring temperature 700, the injection rate of the microstructure of 2m/s when casting, the organization born α-al phase of dendrite morphology, once dendrite dendrite trunk thick, only a small number of globular organization of primary α-al phase and the grain size is larger, the eutectic Si phase exhibits a small organization flakiness and short rod; when the injection speed of 3m/s, can be seen from Figure 9(b) out, the organization of primary α-al phase part of the irregular spherical, granular. The figure is relatively smaller grain size, there are more α-al phase and part of the show dendrite morphology, part of the eutectic Si phase changes from short flakiness spherulitic; when the injection speed of 4m/s, Figure 9(c) shows that the primary α-al phase grain size increased significantly phenomenon appeared coarse dendrite morphology, dendrite arm too coarse, globular rarely the primary α-al phase. When the casting temperature reaches 700, the liquid alloy in the casting process, the mold is passed to increase the heat, the temperature of the mold temperature rises rapidly, so that the liquid alloy at a cooling rate slows down, so that the increase of the coagulation time of primary α-al phase grains dimensions have enough time to grow up, appear coarse dendrite morphology in the organization. 130

6 (a) Tensile strength along with shot speed (b) Elongation rate along with shot speed (c) Hardness along with shot speed Figure 10. Changes of mechanical properties along with shot speed As can be seen from Figure 10, in the pouring temperature of 700, with the injection speed is increased tensile strength ADC12 die casting, elongation are showing increasing trend after the first cut. Hardness value of the sample injection speed has been increased with the decline from 82.2HV to 77.9HV. Relative to the pouring temperature of 680 for casting, pouring temperature is 700 Mechanical Properties of Die Casting has obvious decline, the injection speed of 3m/s casting mechanical properties, tensile strength decreased by MPa to MPa, and the pouring temperature 660, injection speed 3m/s casting is almost, but not as good as pouring temperature 660, the tensile strength of the injection rate of 2m/s and 4m/s when casting. Elongation rate from 1.44% down to 1.13%, the hardness of the sample is also reduced by 97.1HV to 78.9HV. It can be seen, when the pouring temperature is too high, too much shrinkage and deterioration of the mechanical properties of the pores will also die castings. Suitable pouring temperature can not only improve the performance of cast padding to prevent the occurrence of defects, to improve the mechanical properties of castings, while generating a vortex with a volume of gas to avoid casting process, so that the wall thickness of 131

7 the casting shrinkage and shrinkage reduced, so that when the volume of the liquid alloy solidification shrinkage is reduced. Considering, for ADC12 aluminum die casting, a suitable pouring temperature is 680. Die-cast aluminum alloy die casting A356 to adopt such defects appear more disk parts, die casting process parameters optimized casting surface quality is not very good, mold filling is not smooth. ADC12 aluminum alloy castings obtained after the switch to outline a clear, did not produce significant die-casting defects, relatively easy casting, such aluminum die casting molds and die casting machine used in this experiment with the good. 5. CONCLUSIONS (1) Die-cast aluminum alloy die casting A356 to adopt such defects appear more disk parts, die casting process parameters optimized casting surface quality is not very good, mold filling is not smooth. ADC12 aluminum die casting for optimizing the technical parameters: the injection pressure is fixed at 100MPa, mold temperature is 260, pouring temperature of 680, injection speed of 3m/s when ADC12 aluminum die casting filling integrity, good surface quality, good mechanical properties: tensile strength of MPa, elongation of 1.44%, a Vickers hardness of 97.1HV. And a clear outline casting obtained, did not produce significant die-casting defects, relatively easy casting, aluminum die casting molds and such this experiment die casting machine with good. (2) With the increase of injection speed, casting the organization of primary α-al phase grain size decreases after the first showing variation increases. Flakiness of the eutectic Si phase also occurs to very fine particulate transformed, with the trend rate of increase and then again flakiness transformation. Internal casting porosity will also increase the number of injection speed increased. Mechanical properties of castings following changes: tensile strength and elongation after the first presentation by reducing variation, the hardness showed gradually decreasing. (3) With the pouring temperature, the casting is gradually increasing the number of internal pores, the organization of primary α-al phase variation of grain size exhibits increased after the first reduction, the mechanical properties of castings: tensile strength, elongation and hardness showing variation increased first and then decreased. 6. OUTLOOK In this study, aluminum die casting much all have a certain amount of internal porosity, pore defects will cast loose, the mechanical properties of the internal structure of the pores decreases and there is a place prone to cracks. In subsequent research in ensuring the quality of the casting surface, internal organization and the prerequisite to further optimize the mechanical properties of the die casting process for porosity defects. ACKNOWLEDGEMENT This research was financially supported by National Natural Science Foundation (Grant no ), Hebei Outstanding Youth Fund Projects (Grant no. YQ ), the Hebei National Science Foundation (Grant no. E ), the Hebei Baoding Science and Technology research and development plan (Grant no. 16ZG009), Science and Technology of Hebei Agricultural University (Grant no. LG and LG201622). REFERENCES E. Aghion, N. Moscovith, A. Arnon (2007) The correlation between wall thickness and properties of HPDC Magnesium alloys, Materials Science and Engineering: A. 447(1-2), pp H.D. Zhao, F. Wang, Y.Y. Li, W. Xia, (2009) Experimental and numerical analysis of gas entrapment defects in plate ADC12 die castings, Journal of Materials Processing Technology. 209(9), pp Jiang W M, Fan Z T, Liu D J, et al. (2012) Influence of process parameters on filling ability of A356 aluminium alloy in expendable pattern shell casting with vacuum and low pressure, International Journal of Cast Metals Research. 25(1), pp Jiang W M, Fan Z T, Liu D J, et al.(2013) Correlation of microstructure with mechanical properties and fracture behavior of A356-T6 aluminum alloy fabricated by expendable pattern shell casting with vacuum and low-pressure, gravity casting and lost foam casting, Materials Science and Engineering A. 560(1), pp K. Yamada, S. Miyakawa, S. Yoshikawa and A. Hashimoto (2002) Effect of casting defect on the fatigue strength of aluminum die casting materials, Transactions of the Japan Society of Mechanical Engineers A. 68(667), pp

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