OPTIMAL PRODUCTION PROCESS OF PARTICULATE INTERMETALLIC COMPOUND REINFORCED ALUMINIUM METAL MARIX COMPOSITES

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1 International Journal of Aerospace and Lightweight Structures Vol. 3, No. 4 (2014) c Research Publishing Services DOI: /S OPTIMAL PRODUCTION PROCESS OF PARTICULATE INTERMETALLIC COMPOUND REINFORCED ALUMINIUM METAL MARIX COMPOSITES Yongbum Choi 1,, Junichi Murakami 2, Takahiro Motoyama 2, Kazuhiro Matsugi 1, Kenjiro Sugio 1 and Gen Sasaki 1 1 Materials and Production Engineering, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima, , Japan 2 Department of Mechanical Science and Engineering, Hiroshima University, Higashi-Hiroshima, , Japan Al 3 Ni particles reinforced Aluminum alloy composites are fabricated by low pressure infiltration method. To generate Al 3 Ni particles, Nickel porous with 3 different specific surface area were used, 1250 m 2 /m 3, 2800 m 2 /m 3, 5800 m 2 /m 3. Porous nickel reacted with the molten aluminum alloy at 973 k and holding time of 600 s, the applied pressure was 0.1 MPa under furnace cooling. To observe the generated intermetallic compounds, area fraction of Al 3 Ni was investigated. Moreover, the spatial distribution of Al 3 Ni particles was evaluated by analyzing SEM images. Furthermore, the porosity of Al 3 Ni particles reinforced Al metal matrix composites were investigated. Keywords: Metal matrix composites, Nickel porous, Porosity, Aspect ratio, Specific surface area. 1. Introduction Recently, the conversion to aluminum alloy materials from cast iron materials has been increasing. And advanced features of the aluminum alloy are demanded. The composites which are strengthened with ceramic particles in aluminum alloy are developed. It is applied in practical for brake disk and piston in mobile parts in the industrial field [Choi et al., 2006; Yamaguchi, 1991]. Generally, manufacture methods of a ceramic particles dispersed composite include Powder metallurgy process [Pournaderi et al., 2006], Melting stirring method [Seo and Kang, 1995] and Casting method [Gopalakrishnan and Murugan, 2012], etc. Powder metallurgy process requires high cost. Melting agitating method is the process of using the reactivity of melting aluminum and an additive element to manufacture a reaction product. However, fabrication of a complicated-shaped composite is difficult. Address corresponding to Y. B. Choi, Hiroshima University, Higashi-Hiroshima, , Japan; ybchoi@hiroshima-u.ac.jp, TEL:

2 504 Yongbum Choi et al. Casting method is simple fabrication process to make composite. When wettability of an additive element and aluminum is not good, the dispersibility of particles in matrix is a problem. Moreover, when a composite material is applied as piston head or ring portion by the conventional producing method, it raises many problems. Whereas, in this research ceramic particles reinforced composite is applied to the piston head and ring portion of piston parts, which is why the development of a new process is purposed. In the previous study [Sugio et al., 2007], intermetallic compounds particle reinforced metal matrix composite was developed to use reaction between porous nickel and molten Al alloy. However, evaluation of quantification is not carried out to distribute of an intermetallic compounds. Furthermore, many defects exist inside of material. The objective of this research is to investigate the effects of the specific surface area on the intermetallic compounds formed in the composites. Therefore, the research investigated on the amounts of the intermetallic compounds and the distribution of intermetallic compounds by different specific surface area of porous nickel. In addition, the porosity inside composites by various applied pressure of molten aluminum alloy was also investigated, respectively. 2. Experimental 2.1. Materials and Mechanical Tests A366 Alloy in ASTM with Composition of Al-12Si-1Ni-1Cu-1Mg (mass. %), was used as matrix in this experiment. Preform was porous nickel (Toyama Sumitomo Electric Co., Ltd.). Volume ratio of porous nickel is 4 6 vol. %. Figure 1(a c) shows SEM images of porous nickel. Porous nickel has three-dimensional network structure like sponge, large surface area and it is easy to machine. Porous nickels with three different kinds of specific surface areas (a: 1250m 2 /m 3, b: 2800m 2 /m 3 and c: 5800m 2 /m 3 ) were used in the experiment to examine the reactive behavior of the intermetallic compound. Low pressure infiltration method was used to fabricate the composites. Temperature of molten Al alloy was 973K. Furnace cooling is performed after keeping applied pressure for 10 minutes at the temperature of 973 K. After holding for 10 minutes, then wait till the furnace cools, composites were fabricated for pressure on each condition to the constant applied pressure under 0.1 MPa and multi-applied pressure until 0.2 MPa. Figure 1(d) shows the applied conditions of low-pressure infiltration method. These fabrication conditions of temperature of molten Al alloy and holding time are most suitable for generation of the intermetallic compound from previous study [Choi, 2013]. Microstructure of the composites was observed by Scanning Electron Microscope (SEM). And the distribution of intermetallic compounds and pores inside of the composite were measured by picture analysis using the image pro-plus.

3 Optimal Production Process of Particulate Intermetallic Compound 505 (a) (b) 500 m 500 m (c) Temperature of molten alloy, T/K 973K (d) RT 500 m Applied pressure, P/MPa 0.2MPa 0.1MPa Multi-pressure Constant pressure 0 10 Time, t/min Fig. 1. SEM images of porous nickel (Specific surface area: (a) 1250 m 2 /m 3, (b) 2800 m 2 /m 3 and (c) 5800 m 2 /m 3 ) and (d) is experimental conditions of variance applied pressure under low-pressure casting Evaluation of the Spatial Distribution of Al 3 Ni Particles Spatial distribution of Al 3 Ni particles was evaluated by analyzing SEM images of composites using three different kinds of specific surface areas of porous nickel. Spatial distributions are generally divided into ordering distribution, uniform random distribution, and clustering distribution, as shown in Fig. 2. In order to evaluate these distributions quantitatively, 2-dimensions local number (LN2D) was used. The number of gravity centers (GCs) of particles in the measuring circle, whose center is put at GC of a noticed particle, was defined as LN2D. The radius of the measuring circle was determined so that the number density of the circle including GCs of 7 particles corresponds to the whole number density in 2-dimension, where 7 means the number of a noticed particle and nearest neighbor particles in the measuring circle when assuming the closest hexagonal structure. The measuring radius, R 2D, is represented by Eq. (1): 7 πr 2D 2 = λ A R 2D = ( 7 πλ A ) 1/2 = where λ A is the whole number density. When GCs of second phase particles have the uniform random arrangement in 2-dimension, we can expected that the relative frequency distribution of LN2D exhibits modified Poisson distribution and the probability of LN2D is represented by Eq. (2) λ 1/2 A P(LN2D = k + 1) = 7k exp( 7) k = 0, 1, 2... (2) k! (1)

4 506 Yongbum Choi et al. (a)ordering distribution (b)uniform random distribution (c)clustering distribution Fig. 2. Classification of spatial distribution of second phase particles. The average and variance of this distribution are 8 and 7, respectively. Average and variance of LN2D are defined as LN2Dav and LN2Dvar, respectively [Sugio et al., 2007]. Figure. 2(b ) shows the relative frequency of LN2D when GCs of second phase particles have the uniform random arrangement in 2-dimension. Figure 2(a ) shows the one when GCs of second phase particles have the ordering arrangement in 2-dimension, and variance is small compared with Fig. 2(b ). Figure 2(c ) shows the one when GCs of second phase particles have the clustering arrangement in 2-dimension. Average and variance are large compared with Fig. 2(b ). These results were obtained by computer calculation [Sugio et al., 2007]. However, these are only when second phase particles don t have volume. The degree of freedom of the GCs decreases with increasing volume (area) fraction of the second phase particles. Relative frequency distribution of LN2D changes with changing area fraction of the second phase particles, and there is specific uniform spatial arrangement (values of LN2Dav and LN2Dvar) for each area fraction of second phase particles. From computer calculation, it turned out that change of LN2Dav was small, but change of LN2Dvar was large [Sugio et al., 2007]. It indicates that LN2Dvar is sensitive to spatial distribution, and LN2Dvar can be used as a simple descriptor for the

5 Optimal Production Process of Particulate Intermetallic Compound 507 Matrix Al 3 Ni Al 3 Ni 2 Al 3 Ni Al 3 Ni 2 Ni Ni 20 m 20 m Fig. 3. Reaction between molten Al alloy and porous nickel (Specific surface area: 1250 m 2 /m 3 ). spatial distribution. Therefore, in this experiment, LN2Dvar was used to evaluate the spatial distribution of Al 3 Ni particles. 3. Results 3.1. Reaction of Porous Nickel and Molten Alloy Figure 3 shows SEM images of porous nickel (specific surface area: 1250m 2 /m 3 ) reinforced A366 alloy composite. Molten Al alloy of 973 K was infiltrated to porous nickel by using low pressure infiltration at 0.1 MPa. EDX analysis confirmed the existence of Al 3 Ni phase, nickel phase at the central section of porous nickel and an Al 3 Ni 2 phase between the Al 3 Ni and nickel [Matsumuro and Kitsudo, 2006]. Other intermetallic compounds were not detected. The phase formation sequence was described as following Eq. (3): 3Al + Ni Al 3 Ni 190 kj/mol (3) These observations were consistent with the report by Hibinoon the rate of formation of Ni-Al intermetallic compounds [Kubaschewski, 1993]. As seen in Fig. 4, the porous nickel does not instantly react and change to Al 3 Ni. On the contrary, the reaction between the molten Al alloy and porous nickel gradually proceeds, working Fig. 4. Microstructure of Al 3 Ni/A366 composites with specific surface area of porous: 1250 m 2 /m 3 (a), 2800 m 2 /m 3 (b) and 5800 m 2 /m 3 (c) fabricated conditions at 973K and 0.1MPa.

6 508 Yongbum Choi et al. towards the center of the porous nickel from the outer surface and fine Al 3 Ni are dispersed into the matrix. In light of the densities of the Ni, Al 3 Ni 2 and Al3Ni, i.e., 8.9, 4.8 and 4.0kg/m 3, the porous nickel is thought to undergo an expansion reaction with the molten Al alloy [Hibino, 1993] Effect of the Specific Surface Area of Porous Nickel Figure 4 shows microstructure of Al 3 Ni/A366 composites with specific surface area of porous: 1250m 2 /m 3 (a), 2800m 2 /m 3 (b) and 5800m 2 /m 3 (c) fabricated at 973K and 0.1MPa. Molten Al alloy was infiltrated to the porous nickel at applied pressure of 0.1 MPa. As a result of observing the microstructure of the composites manufactured using three different kinds of porous nickel, on the whole, the intermetallic compound was distributed inside matrix by the reaction of a porous nickel and aluminum. However, As a result of observing an microstructure when specific surface area is low (in Fig. 4(a) 1250m 2 /m 3 ), almost all porous nickel were changed to intermetallic compound, but the portion which remains as porous body without delamination from the porous surface was also observed. Most of the fine Al 3 Ni intermetallic compounds were homogeneously dispersed. But shape of the needle-like Al 3 Ni and numerous pores were observed in the composites. As a result of observing an microstructure when specific surface area is high (in Fig. 4(c) 5800m 2 /m 3 ), Al3Ni 3 Ni Un Un-reacted Ninickel Area fraction (%) Specific surface area,s/m 2 /m 3 Fig. 5. Area fraction of Al 3 Ni intermetallic compounds.

7 Optimal Production Process of Particulate Intermetallic Compound 509 Table 1. Area fraction of intermetallic compounds by three different specific surface area. Specific surface area (m 2 /m 3 ) Area fraction (%) Al 3 Ni Un-reacted nickel Many fined intermetallic compounds were distributed as compared with other materials in Fig. 4(a) and (b). Fine intermetallic compounds increased with increasing specific surface area of porous nickel. In addition, based on the Fig. 4(c) and Fig. 5, it showed that the area fraction (%) of intermetallic compound Al 3 Ni was 27%, which is almost twice of Fig. 5(a). Furthermore, the area fraction of un-reacted Ni reached a minimum value of 0.21 vol. % when the specific surface was 5800m 2 /m 3. The results of each area fraction of intermetallic compound by three different specific surface area is shown in Table 1. Besides, the results indicate that higher the specific surface is, larger the contact surface of porous nickel with molten Al alloy is, and it provided further reaction of Ni with Al Spatial Distribution of Al 3 Ni Intermetallic Compound Figure 6 shows plots of LN2Dvar of Al 3 Ni/A366 composites with three different kinds of porous nickel versus area fraction of particles. The theoretical value derived from Eq. (2) is also plotted at area fraction of 0.0, where LN2Dvar were 7. The line of uniform spatial distribution was obtained from computer calculations 10 8 Uniform random 1250 Specific surface area:1250m 2 /m Specific surface area:2800m 2 /m Specific surface area:5800m 2 /m 3 LN2D var 6 4 Clustering distribution 2 Ordering distribution Area fraction Fig. 6. Evaluation of Al 3 Ni particle spatial distributions.

8 510 Yongbum Choi et al. Specific surface area (m 2 /m 3 ) Table 2. Evaluation of Al 3 Ni particle spatial distribution. (a) Values by Exp. LN2D var (b) Values by Cal. of uniform random (a) (b) [Sugio et al., 2007]. With increasing area fraction, LN2Dvar decrease monotonically. It indicates that LN2Dvar is sensitive to spatial distribution, and LN2Dvar can be used as a simple descriptor for the spatial distribution. Clustering distribution area is above this line, and ordering distribution area is below this line. All Al 3 Ni/A366 composites with specific surface area of porous: 1250m 2 /m 3, 2800m 2 /m 3 and 5800m 2 /m 3 exhibit clustering tendency. Table 2 shows the differences between values of each composites LN2Dvar and ones of uniform random distribution for each area fractions of composites. It becomes smaller with increasing specific surface area of porous nickel. This means that spatial distribution of Al 3 Ni particle approaches uniform random and ordering distribution with increasing specific surface area of porous nickel. Cell size of porous nickel used in this experiment decreases with Porosity(%) Multi-applied pressure Specific surface area,s/m 2 /m 3 Constant applied pressure (a) (b) (a) Constant applied pressure Pore 500 m (b) Multi-applied pressure Pore 500 m Fig. 7. Porosity in composite, constant applied pressure of 0.1 MPa and multi-applied pressure of 0.2MPa.

9 Optimal Production Process of Particulate Intermetallic Compound 511 increasing specific surface area. It suggests that Al 3 Ni which were produced at interface between Ni porous and molten Al are dispersed into the matrix easily with increasing specific surface area Porosity of Composites by Multi-Applied Pressure As shown in Fig. 8, the porosity in Al 3 Ni/A366 alloy composite varies according to the variation of the specific surface area of porous nickel both in porous nickel and matrix. Figure 7(a) and (b) shows the place where each pores exists. Figure 7(a) is pore in porous nickel. Figure 7(b) is pore in matrix. The general porosity trend in both porous nickel and matrix is reducing with the increasing of the specific surface area, and the minimum porosity is about 0.2% in the matrix and 0.4% in the porous nickel of 5800m 2 /m 3 since with the reduction of the porous thickness accelerated the reaction between Ni and Al and delamination caused by the difference of thermal expiation coefficient with nickel, which is a great reduction of defect in the composites as well. 4. Conclusions Microstructure observation of the intermetallic compound reinforced Al alloy composites fabricated using three kinds of porous nickel is performed, and distribution of an intermetallic compound is quantified. In order to decrease the pores inside composite, applied pressure was controlled. The results are listed below. 1) The porous nickel does not instantly react and change to Al 3 Ni. The reaction between the molten Al alloy and porous nickel gradually proceeds, working towards the center of the porous nickel from the outer surface and fine Al 3 Ni are dispersed into the matrix. In light of the densities of the Ni, Al 3 Ni 2 and Al 3 Ni, i.e., 8.9, 4.8 and 4.0 kg/m 3, the porous nickel is considered to undergo an expansion reaction with the molten Al alloy. 2) The microstructures of the composites manufactured using three kinds of porous nickel were investigated. The intermetallic compound was distributed into the matrix by the reaction of porous nickel and aluminum. When specific surface area is high, almost all porous nickel were changed into intermetallic compound and the size of intermetallic compound is smaller compared with low specific surface area of porous nickel. 3) The composites manufactured using three kinds of porous nickel exhibit clustering tendency. Spatial distribution of Al 3 Ni particle approaches uniform random and ordering distribution with increasing specific surface area of porous nickel. 4) The Pores inside composites decreased with increasing specific surface area. Also, the pores inside the composite fabricated for multi-applied pressure was additionally reduced to 0.2% porosity.

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