- Email: [email protected]
Effect of thermomagnetic treatment on tensile properties of Al18B4O33 whisker-reinforced aluminum composite containing Fe3O4 particles
Materials Letters 57 (2003) 3217 – 3221 www.elsevier.com/locate/matlet
Effect of thermomagnetic treatment on tensile properties of Al18B4O33 whisker-reinforced aluminum composite containing Fe3O4 particles G. Li, Y. Sun, W.D. Fei * School of Materials Science and Engineering, Harbin Institute of Technology, P.O. Box 433, Harbin 150001, PR China Received 18 November 2002; accepted 8 January 2003
Abstract A new aluminum borate whisker-reinforced aluminum composite containing Fe3O4 particles was fabricated using squeezecasting method. The microstructure and tensile properties of the composite were investigated. The results show that the thermomagnetic treatment with a pulse field is an effective technique to enhance the ultimate tensile strength and plasticity of the composite. On the basis of the analysis of broadening effect of X-ray diffraction peak, the mechanism of the effect of pulsedfield thermomagnetic treatment on the tensile properties of the composite was discussed. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Aluminum; Composite materials; Fe3O4 particle; Thermomagnetic treatment; Mechanical properties
1. Introduction Aluminum borate whisker (Al18B4O33w, denoted by ABOw)-reinforced aluminum composite has been extensively investigated on account of good mechanical properties and fairly low cost [1,2]. As with other aluminum matrix composites reinforced by ceramics, higher thermal mismatch stress (TMS) may be generated by the great difference of coefficients of thermal expansion (CTE) between the matrix and the reinforcement [3]. TMS has some disadvantageous effects on the properties of composite, such as yield strength, fatigue life, dimension stability, etc. [4– 6],
* Corresponding author. Fax: +86-451-6413922. E-mail address: [email protected] (W.D. Fei).
which limit the application of the composite in some precision structure parts. Therefore, it is very important to develop an effective method to reduce the TMS in the composite. For the parts of iron and steel, it was indicated that the magnetic treatment could reduce effectively the residual stress in them [7]. In the present study, Fe3O4 particle with magnetostrictive property was added into the ABOw/Al composite, and the dimension of Fe3O4 particle will change with the frequency of the external pulse magnetic field. In this case, it is expected that the TMS in the composite can be reduced and the tensile strength of the composite can be enhanced when the composite is treated under a pulse magnetic treatment. The obvious effect of thermomagnetic treatment on the tensile properties of ABOw/Al composite contain-
0167-577X/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(03)00038-7
3218
G. Li et al. / Materials Letters 57 (2003) 3217–3221
ing Fe3O4 particles was observed and reported in the present paper.
2. Experimental The materials used are pure aluminum, Fe3O4 particle with a diameter of 40– 60 Am and aluminum borate whisker with a diameter of 0.5 – 1 Am and length of 10– 30 Am. The composite was fabricated by squeeze-casting technique. The total volume fraction of Fe3O4 particle and aluminum borate whisker is 24%, and the volume ratio between Fe3O4 particle and aluminum borate whisker is about 1:4. To prevent the interaction between Fe3O4 particle and aluminum, the Fe3O4 particles were coated with Al2O3 using a chemical method. The pressure of squeeze casting was 200 MPa. The casting temperature of pure aluminum was 800 jC and the die temperature was about 520 jC. Tensile specimens with the dimension shown in Fig. 1 were cut from the composite ingot. The specimens were theromagnetically treated at 100 jC for 1 h with a pulsed magnetic field of about 400 kA/m perpendicular to the section plane of tensile specimen. The microstructure and fractograph were examined using optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The specimens for TEM observation were thinned by means of ion milling. The XRD test in the step scanning model with the step size of 0.02j was carried out on a Philips X’pert X-ray diffractometer. The radiation used was Cu Ka with the operation voltage of 40 kV and the current of
Fig. 1. Dimension of a tensile specimen (mm).
Fig. 2. OM micrograph of (Fe3O4 + ABOw)/Al composite.
40 mA. The double lines of Ka1 and Ka2 were automatically separated by computer.
3. Results and discussion 3.1. Microstructure and tensile properties The OM and SEM images of the microstructure of the composite are shown in Figs. 2 and 3, respectively. It can be found that the distribution of Fe3O4 particles
Fig. 3. SEM micrograph of (Fe3O4 + ABOw)/Al composite.
G. Li et al. / Materials Letters 57 (2003) 3217–3221
and aluminum borate whiskers in the composite is random and homogeneous. TEM photographs are shown in Fig. 4; the selected area electron diffraction pattern (SADP) given in Fig. 4b shows that the particles in Fig. 4a are Fe3O4, which suggests that no heavier interfacial reaction between the particles and aluminum matrix takes place during squeezecasting process. The comparison of ultimate tensile strengths (UTS) of as-cast, thermally treated and thermomagnetically treated (Fe3O4 + ABOw)/Al composite is given in Fig. 5. It can be seen that the UTS of ascast (Fe3O4 +ABOw)/Al composite is above 240 MPa that is much higher than 55 MPa of UTS of pure aluminum, that is to say, the quality of (Fe3O4 + ABOw)/Al composite fabricated in the present study is good. After thermomagnetic treatment, the UTS of
Fig. 4. TEM photos of (Fe3O4 + ABOw)/Al composite: (a) micrograph, (b) SADP.
3219
Fig. 5. Tensile strength of (Fe3O4 + ABOw)/Al composite.
the composite is enhanced to about 320 MPa, which is much higher than those of as-cast composite and the composite thermally treated without magnetic field. Therefore, the thermomagnetic treatment is a very effective technique to enhance the UTS of (Fe3O4 + ABOw)/Al composite. The stress –strain curves of the composites before and after thermomagnetic treatment are shown in Fig. 6. It is clear that the elongation or plasticity of the composite was increased obviously through the thermomagnetic treatment. Fig. 7 shows the tensile fractographs of the specimens. Many dimples can be found in the fratographs, which results from the toughening fracture of the matrix. Meanwhile, no crack can be found in the fractograph, which indicates that the interface bonding between whiskers and Al, particles and Al are better.
Fig. 6. Stress – strain curves of the (Fe3O4 + ABOw)/Al composite.
3220
G. Li et al. / Materials Letters 57 (2003) 3217–3221
3.2. Residual strain The TMS in aluminum matrix is tensile, which has been confirmed by many previous studies [8,9]. It is not easy to measure TMS directly for the complicated materials system. However, it may be possible that the XRD peak width of aluminum matrix can be employed to reveal indirectly the changing tendency of TMS in the composite. The broadening effect of diffraction peaks of the matrix may result from three aspects in the case of present study. Firstly, the fine grain brings a broadening effect for the diffraction peaks [10]. Secondly, the increased defect density in the matrix also leads to a broadening effect of diffraction peaks. Thirdly, the diffraction peaks can be broadened by residual strain in the matrix. The distribution of whiskers and particles is considered to be random in the composite fabricated by squeeze-casting technique and the longitudinal directions of the whiskers are random, too (as shown in Figs. 2 and 3). The whiskers in the volume irradiated by X-ray are also random since there are so many whiskers in it. Because the magnitude of residual strain along the longitudinal direction of whiskers is different from that along the direction perpendicular to the longitudinal direction of whiskers [8], the larger the TMS, the broader the diffraction peak.
Fig. 8. Integral breadth of 111-diffraction peak of Al matrix of (Fe3O4 + ABOw)/Al composite.
In the present study, the grain size and the defect density do not change or change little, which arise from lower temperature and shorter time of the heat treatment. Therefore, the width of diffraction peak of aluminum matrix can be employed to characterize the TMS in the composite. It is clear that the smaller the width of aluminum peak, the lower the TMS in the composite. Integral breadth of 111-diffraction peak of Al matrix in the composites before and after thermomagnetic treatments is shown in Fig. 8. After thermomagnetic treatment, the integral breadth of 111-peak of Al matrix is decreased obviously. Therefore, we think that the thermomagnetic treatment can reduce the TMS of Al matrix of (Fe3O4 + ABOw)/Al composite. Because of the magnetostrictive properties of Fe3O4 particles, the size of Fe3O4 particle may alter periodically with the change of external magnetic field, which may cause the TMS relaxation in Al matrix, in turn result in the increasing of the tensile strength and plasticity of composite.
4. Summary
Fig. 7. Tensile fractograph of as-cast (Fe3O4 + ABOw)/Al composite.
In this work, we successfully developed an aluminum matrix composite reinforced by both Fe3O4 particle and aluminum borate whisker, and higher tensile strength was attained in the composite. It is found that the UTS and plasticity of the composite can be enhanced greatly by thermomagnetic treatment at 100 jC with a pulse magnetic field. Although the
G. Li et al. / Materials Letters 57 (2003) 3217–3221
detailed mechanism of the effect of thermomagnetic treatment on the mechanical properties of the composite is not clear, the decrease of TMS in the composite subjected to the thermomagnetic treatment may be a main reason for the improvement of tensile properties of (Fe3O4 + ABOw)/Al composite.
References [1] K. Suganuma, T. Fujita, N. Suzuki, K. Niihara, J. Mater. Sci. Lett. 9 (1990) 633. [2] J. Hu, W.D. Fei, C. Li, C.K. Yao, Mater. Sci. Technol. 1 (1993) 1 (in Chinese).
3221
[3] W.D. Fei, Q.Y. Liu, N.G. Liang, C.K. Yao, Mater. Sci. Technol. 17 (2001) 912. [4] H.Y. Zhang, P.M. Anderson, G.S. Daehn, Metall. Mater. Trans. 25A (1994) 415. [5] L.C. Davis, J.E. Alliwon, Metall. Mater. Trans. 24A (1993) 2487. [6] R.J. Arsenault, S.B. Wu, Mater. Sci. Eng. 96 (1987) 77. [7] F. Tang, A.L. Lu, J.F. Mei, H.Z. Fang, X.J. Luo, J. Mater. Process. Technol. 74 (1988) 255. [8] R.J. Arsenault, M. Taya, Acta Metall. 35 (1987) 651. [9] Z.M. Sun, J.B. Li, Z.G. Wang, Acta Metall. Mater. 40 (1992) 2961. [10] V. Ji, Y.G. Zhang, C.Q. Chen, Surf. Coat. Technol. 130 (2000) 95.
Effect of thermomagnetic treatment on tensile properties of Al18B4O33 whisker-reinforced aluminum composite containing Fe3O4 particles G. Li, Y. Sun, W.D. Fei * School of Materials Science and Engineering, Harbin Institute of Technology, P.O. Box 433, Harbin 150001, PR China Received 18 November 2002; accepted 8 January 2003
Abstract A new aluminum borate whisker-reinforced aluminum composite containing Fe3O4 particles was fabricated using squeezecasting method. The microstructure and tensile properties of the composite were investigated. The results show that the thermomagnetic treatment with a pulse field is an effective technique to enhance the ultimate tensile strength and plasticity of the composite. On the basis of the analysis of broadening effect of X-ray diffraction peak, the mechanism of the effect of pulsedfield thermomagnetic treatment on the tensile properties of the composite was discussed. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Aluminum; Composite materials; Fe3O4 particle; Thermomagnetic treatment; Mechanical properties
1. Introduction Aluminum borate whisker (Al18B4O33w, denoted by ABOw)-reinforced aluminum composite has been extensively investigated on account of good mechanical properties and fairly low cost [1,2]. As with other aluminum matrix composites reinforced by ceramics, higher thermal mismatch stress (TMS) may be generated by the great difference of coefficients of thermal expansion (CTE) between the matrix and the reinforcement [3]. TMS has some disadvantageous effects on the properties of composite, such as yield strength, fatigue life, dimension stability, etc. [4– 6],
* Corresponding author. Fax: +86-451-6413922. E-mail address: [email protected] (W.D. Fei).
which limit the application of the composite in some precision structure parts. Therefore, it is very important to develop an effective method to reduce the TMS in the composite. For the parts of iron and steel, it was indicated that the magnetic treatment could reduce effectively the residual stress in them [7]. In the present study, Fe3O4 particle with magnetostrictive property was added into the ABOw/Al composite, and the dimension of Fe3O4 particle will change with the frequency of the external pulse magnetic field. In this case, it is expected that the TMS in the composite can be reduced and the tensile strength of the composite can be enhanced when the composite is treated under a pulse magnetic treatment. The obvious effect of thermomagnetic treatment on the tensile properties of ABOw/Al composite contain-
0167-577X/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(03)00038-7
3218
G. Li et al. / Materials Letters 57 (2003) 3217–3221
ing Fe3O4 particles was observed and reported in the present paper.
2. Experimental The materials used are pure aluminum, Fe3O4 particle with a diameter of 40– 60 Am and aluminum borate whisker with a diameter of 0.5 – 1 Am and length of 10– 30 Am. The composite was fabricated by squeeze-casting technique. The total volume fraction of Fe3O4 particle and aluminum borate whisker is 24%, and the volume ratio between Fe3O4 particle and aluminum borate whisker is about 1:4. To prevent the interaction between Fe3O4 particle and aluminum, the Fe3O4 particles were coated with Al2O3 using a chemical method. The pressure of squeeze casting was 200 MPa. The casting temperature of pure aluminum was 800 jC and the die temperature was about 520 jC. Tensile specimens with the dimension shown in Fig. 1 were cut from the composite ingot. The specimens were theromagnetically treated at 100 jC for 1 h with a pulsed magnetic field of about 400 kA/m perpendicular to the section plane of tensile specimen. The microstructure and fractograph were examined using optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The specimens for TEM observation were thinned by means of ion milling. The XRD test in the step scanning model with the step size of 0.02j was carried out on a Philips X’pert X-ray diffractometer. The radiation used was Cu Ka with the operation voltage of 40 kV and the current of
Fig. 1. Dimension of a tensile specimen (mm).
Fig. 2. OM micrograph of (Fe3O4 + ABOw)/Al composite.
40 mA. The double lines of Ka1 and Ka2 were automatically separated by computer.
3. Results and discussion 3.1. Microstructure and tensile properties The OM and SEM images of the microstructure of the composite are shown in Figs. 2 and 3, respectively. It can be found that the distribution of Fe3O4 particles
Fig. 3. SEM micrograph of (Fe3O4 + ABOw)/Al composite.
G. Li et al. / Materials Letters 57 (2003) 3217–3221
and aluminum borate whiskers in the composite is random and homogeneous. TEM photographs are shown in Fig. 4; the selected area electron diffraction pattern (SADP) given in Fig. 4b shows that the particles in Fig. 4a are Fe3O4, which suggests that no heavier interfacial reaction between the particles and aluminum matrix takes place during squeezecasting process. The comparison of ultimate tensile strengths (UTS) of as-cast, thermally treated and thermomagnetically treated (Fe3O4 + ABOw)/Al composite is given in Fig. 5. It can be seen that the UTS of ascast (Fe3O4 +ABOw)/Al composite is above 240 MPa that is much higher than 55 MPa of UTS of pure aluminum, that is to say, the quality of (Fe3O4 + ABOw)/Al composite fabricated in the present study is good. After thermomagnetic treatment, the UTS of
Fig. 4. TEM photos of (Fe3O4 + ABOw)/Al composite: (a) micrograph, (b) SADP.
3219
Fig. 5. Tensile strength of (Fe3O4 + ABOw)/Al composite.
the composite is enhanced to about 320 MPa, which is much higher than those of as-cast composite and the composite thermally treated without magnetic field. Therefore, the thermomagnetic treatment is a very effective technique to enhance the UTS of (Fe3O4 + ABOw)/Al composite. The stress –strain curves of the composites before and after thermomagnetic treatment are shown in Fig. 6. It is clear that the elongation or plasticity of the composite was increased obviously through the thermomagnetic treatment. Fig. 7 shows the tensile fractographs of the specimens. Many dimples can be found in the fratographs, which results from the toughening fracture of the matrix. Meanwhile, no crack can be found in the fractograph, which indicates that the interface bonding between whiskers and Al, particles and Al are better.
Fig. 6. Stress – strain curves of the (Fe3O4 + ABOw)/Al composite.
3220
G. Li et al. / Materials Letters 57 (2003) 3217–3221
3.2. Residual strain The TMS in aluminum matrix is tensile, which has been confirmed by many previous studies [8,9]. It is not easy to measure TMS directly for the complicated materials system. However, it may be possible that the XRD peak width of aluminum matrix can be employed to reveal indirectly the changing tendency of TMS in the composite. The broadening effect of diffraction peaks of the matrix may result from three aspects in the case of present study. Firstly, the fine grain brings a broadening effect for the diffraction peaks [10]. Secondly, the increased defect density in the matrix also leads to a broadening effect of diffraction peaks. Thirdly, the diffraction peaks can be broadened by residual strain in the matrix. The distribution of whiskers and particles is considered to be random in the composite fabricated by squeeze-casting technique and the longitudinal directions of the whiskers are random, too (as shown in Figs. 2 and 3). The whiskers in the volume irradiated by X-ray are also random since there are so many whiskers in it. Because the magnitude of residual strain along the longitudinal direction of whiskers is different from that along the direction perpendicular to the longitudinal direction of whiskers [8], the larger the TMS, the broader the diffraction peak.
Fig. 8. Integral breadth of 111-diffraction peak of Al matrix of (Fe3O4 + ABOw)/Al composite.
In the present study, the grain size and the defect density do not change or change little, which arise from lower temperature and shorter time of the heat treatment. Therefore, the width of diffraction peak of aluminum matrix can be employed to characterize the TMS in the composite. It is clear that the smaller the width of aluminum peak, the lower the TMS in the composite. Integral breadth of 111-diffraction peak of Al matrix in the composites before and after thermomagnetic treatments is shown in Fig. 8. After thermomagnetic treatment, the integral breadth of 111-peak of Al matrix is decreased obviously. Therefore, we think that the thermomagnetic treatment can reduce the TMS of Al matrix of (Fe3O4 + ABOw)/Al composite. Because of the magnetostrictive properties of Fe3O4 particles, the size of Fe3O4 particle may alter periodically with the change of external magnetic field, which may cause the TMS relaxation in Al matrix, in turn result in the increasing of the tensile strength and plasticity of composite.
4. Summary
Fig. 7. Tensile fractograph of as-cast (Fe3O4 + ABOw)/Al composite.
In this work, we successfully developed an aluminum matrix composite reinforced by both Fe3O4 particle and aluminum borate whisker, and higher tensile strength was attained in the composite. It is found that the UTS and plasticity of the composite can be enhanced greatly by thermomagnetic treatment at 100 jC with a pulse magnetic field. Although the
G. Li et al. / Materials Letters 57 (2003) 3217–3221
detailed mechanism of the effect of thermomagnetic treatment on the mechanical properties of the composite is not clear, the decrease of TMS in the composite subjected to the thermomagnetic treatment may be a main reason for the improvement of tensile properties of (Fe3O4 + ABOw)/Al composite.
References [1] K. Suganuma, T. Fujita, N. Suzuki, K. Niihara, J. Mater. Sci. Lett. 9 (1990) 633. [2] J. Hu, W.D. Fei, C. Li, C.K. Yao, Mater. Sci. Technol. 1 (1993) 1 (in Chinese).
3221
[3] W.D. Fei, Q.Y. Liu, N.G. Liang, C.K. Yao, Mater. Sci. Technol. 17 (2001) 912. [4] H.Y. Zhang, P.M. Anderson, G.S. Daehn, Metall. Mater. Trans. 25A (1994) 415. [5] L.C. Davis, J.E. Alliwon, Metall. Mater. Trans. 24A (1993) 2487. [6] R.J. Arsenault, S.B. Wu, Mater. Sci. Eng. 96 (1987) 77. [7] F. Tang, A.L. Lu, J.F. Mei, H.Z. Fang, X.J. Luo, J. Mater. Process. Technol. 74 (1988) 255. [8] R.J. Arsenault, M. Taya, Acta Metall. 35 (1987) 651. [9] Z.M. Sun, J.B. Li, Z.G. Wang, Acta Metall. Mater. 40 (1992) 2961. [10] V. Ji, Y.G. Zhang, C.Q. Chen, Surf. Coat. Technol. 130 (2000) 95.