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Hot compressive deformation behavior of a eutectic Al–Si alloy based composite reinforced with α-Si3N4 whisker
Materials Chemistry and Physics 82 (2003) 618–621
Hot compressive deformation behavior of a eutectic Al–Si alloy based composite reinforced with ␣-Si3N4 whisker A.H. Feng, L. Geng∗ , J. Zhang, C.K. Yao School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China Received 15 May 2003; accepted 6 June 2003
Abstract Elevated temperature compressive deformation behavior of a 4032 aluminum alloy matrix composite reinforced with 20 vol.% ␣-Si3 N4 whisker was investigated at the strain rate from 0.016 to 1.0 s−1 . The deformation temperatures were below and above the solidus temperature of the composite, which was determined by differential scanning calorimeter (DSC). It was found that the flow stress of the composite decreased with increasing compressive temperature. The microstructure of the composite was observed and analyzed by using optical microscope (OM) and TEM. The morphology of eutectic Al–Si was found to plays an important role in the compressive deformation behavior of the composite. In addition, there are interfacial reactions between the matrix alloy and the Si3 N4 whiskers due to segregation of the alloy elements near the matrix/reinforcement interfaces. © 2003 Elsevier B.V. All rights reserved. Keywords: Deformation; DSC; TEM; Composite materials
1. Introduction
2. Experimental materials and procedures
Al–Si alloys have been widely used as aluminum casting alloys because of their attractive physical and mechanical properties, especially the Si microstructure as a function of growth conditions [1,2]. Extensive researches [3–8] have been carried out on the microstructures of the Al–Si alloys as a function of nucleation and growth conditions during the solidification process, but relatively little work has focused on the compressive deformation of the Si3 N4 w/Al–Si composites. Compressive deformation is a valuable way to study the plastic deformation of metal matrix composites. Based on the Al–Si phase diagram, the basic microstructure is primary aluminum solution and Al–Si eutectic phase for 4032 Al alloy. The morphology of eutectic Al–Si and primary aluminum solution play an important role in determining the mechanical properties of these alloys. The focus of this study is mainly on the compressive characteristics and the effect of eutectic Al–Si on the elevated temperature compressive deformation behavior of the ␣-Si3 N4 w/4032 Al composite.
The ␣-Si3 N4 w/4032 Al composite with 20% volume fraction of the reinforcement was fabricated by squeeze casting. The composition of the 4032 alloy is as follows: 11.5 wt.% Si, 0.8–1.3 wt.% Mg, 0.5–1.3 wt.% Cu, 0.5–1.3 wt.% Ni and balance Al. The reinforcement material is ␣-Si3 N4 whisker with an average length of 20 m. In the present investigation, the compressive deformation was carried out over a wide temperature range of 773–873 K, including the temperatures below and above the solidus temperature of the composite. The solidus temperature of the composite was determined by using differential scanning calorimeter (DSC). Compressive deformation behavior of the composite at elevated temperatures was studied on Gleeble1500 Thermal Simulator. The microstructure of the composite was observed and analyzed by using optical microscope (OM) and TEM.
∗ Corresponding author. E-mail address: [email protected] (L. Geng).
0254-0584/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0254-0584(03)00323-7
3. Results and discussion Fig. 1 shows the DSC analysis results indicating the melting points. The solidus temperature of the Si3 N4 w/4032 Al composite is 810 K and that of the 4032 Al alloy is 805 K. As seen in Fig. 1, two endothermic peaks were observed in each curve, corresponding to eutectic Al–Si peak and
A.H. Feng et al. / Materials Chemistry and Physics 82 (2003) 618–621
0.0
0
-0.5
-1
-1.0 -2 DSC/mW/mg
DSC/mW/mg
619
-3 -4
-2.0 -2.5
-5 -6 300
-1.5
-3.0 400
500
600
700
Temperature
-3.5 300
400
500
600
700
Temperature
Fig. 1. The DSC analysis results of the (a) 4032 Al alloy and (b) Si3 N4 w/4032 composites at 30 K min−1 heating rate.
primary aluminum solution peak, respectively. The first endothermic peak at lower temperature corresponds to the fusion of the eutectic Al–Si and the second endothermic peak at higher temperature refers to the fusion of the primary aluminum solution. The endothermic peak of the Si3 N4 w/4032 Al composite may be completed earlier than the 4032 Al
matrix. The possible reason is the more interfaces in the Si3 N4 w/4032 Al composite and the morphology of primary aluminum solution changed from dendrite-like to equiaxed due to the addition of Si3 N4 whisker. Microstructure of the Si3 N4 w/4032 Al composite and the 4032 Al matrix is shown in Fig. 2. The microstructure of
Fig. 2. The microstructure of the 4032 Al matrix composite and Si3 N4 w/4032 Al composite (a) the 4032 Al alloy before being compressed; (b) the 4032 Al alloy after being compressed (T =833 K, ε˙ = 0.37 s−1 ); (c) the Si3 N4 w/4032 composite before being compressed and (d) the Si3 N4 w/4032 composite after being compressed (T =773 K, ε˙ = 0.37 s−1 ).
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Si3N4w/4032Al 4032Al
80
Si3N4w/4032Al 4032Al
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60
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50 40 30 20
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Fig. 3. The true stress–true strain curves of the Si3 N4 w/4032 Al composite and the 4032 Al alloy compressed with a strain rate of 0.37 s−1 at different temperatures (a) T =773 K; (b) T =813 K; (c) T =833 K and (d) T =853 K.
4032 Al alloy consist of primary aluminum solution dendrites and eutectic Al–Si. The eutectic Al–Si distribution along the Al grain boundaries, shows the salient microstructure features. It is clear that the addition of Si3 N4 whiskers leads to a refinement of eutectic Al–Si and primary aluminum solution dendrites. The addition of Si3 N4 whisker changes not only the morphology of primary aluminum solution from dendrite-like to equiaxed, but also the morphology of the eutectic Al–Si from netlike to particulate. From Fig. 2(b), when the 4032 Al alloy is compressed at temperature 833 K, partial melting was found to start at the grain boundaries, followed by an apparent decrease in the proportion of eutectic Al–Si phase. Meanwhile, the primary aluminum solution dendrite arms coarsened during hot compressed. Fig. 3 shows the true stress–true strain curves of the Si3 N4 w/4032Al composite and the 4032 Al alloy compressed with a strain rate of 0.37 s−1 at different temperatures. It can be seen that the flow stresses of the Si3 N4 w/4032 Al composite are much higher than that of the 4032 Al alloy at lower temperatures (773 and 813 K), but
the difference becomes quite small at higher temperatures (833 and 853 K). The strength of the composites decreased with increasing compressive temperature. When the composite is compressed at 833 K and above, the liquid phase, resulting from the melting of ternary Al–Si–Mg eutectic at 833 K, appears preferentially at reinforcement/matrix interface or the grain boundaries, resulting in a sharp decrease of load transfer ability of the interface and in turn an obvious decrease of the flow stress of the composite as shown in Fig. 3. When the composite is compressed at 833 K, a larger amount of liquid phase appears, resulting from the melting of binary Al–Si eutectic at 850 K, which does not contribute to large flow stress. This suggests that mechanism of deformation is strongly affected by the volume and distribution of a liquid phase. Microstructure of the compressed Si3 N4 w/4032 Al composites is also characterized by the interfacial reaction. The Si3 N4 whisker is very stable and the interfacial reactions are carried out by the interaction between an amorphous surface layer of the whisker and the segregated Mg atoms in the matrix, resulting in the formation of MgO, MgAl2 O4
A.H. Feng et al. / Materials Chemistry and Physics 82 (2003) 618–621
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Fig. 4. The interfaces of Si3 N4 w/4032 Al composite compressed at different parameters (a) ε˙ = 0.016 s−1 , 793 K; (b) ε˙ = 0.016 s−1 , 813 K and (c) ε˙ = 0.094 s−1 , 853 K.
particles at the interfaces [9]. The interfacial reaction becomes strong with increasing temperature due to segregation of solute atoms near the matrix/reinforcement interfaces as shown in Fig. 4.
Acknowledgements The authors are grateful for the finance support of the National Nature Science Foundation of People’s Republic of China under grant No. 50071018.
4. Conclusion References The microstructure of 4032 Al alloy consist of primary aluminum solution dendrites and Al–Si eutectic. The eutectic Al–Si distributed along the Al grain boundaries, showing the salient microstructure features. It is clear that the addition of Si3 N4 whiskers leads to a refinement of eutectic Al–Si and primary aluminum solution dendrites. The flow stress of the composites decreased with increasing compressive temperature. The morphology of eutectic Al–Si and primary aluminum solution play an important role in determining the compressive properties of these alloys. In addition, there was interfacial reaction between the matrix and Si3 N4 whiskers due to segregation of solute atoms near the matrix/reinforcement interfaces.
[1] [2] [3] [4] [5] [6] [7] [8] [9]
H. Akbulut, M. Durman, F. Yilmaz, Wear 215 (1998) 170. C.R. Ho, B. Cantor, Acta Metal. Mater. 43 (1994) 3231. J. Braszczynski, A. Zyska, Mater. Sci. Eng. A 278 (2000) 195. S. Nagarajan, B. Dutta, M.K. Surappa, Compos. Sci. Technol. 59 (1999) 897. R.-Y. Wang, W.-H. Lu, L.M. Hogan, J. Cryst. Growth 207 (1999) 43. M.O. Pekguleryuz, N. Pedneau, Scripta Mater. 38 (1998) 1533. M. Gupta, S. Ling, J. Alloys Compd. 287 (1999) 284. W.R. Loue, M. Suery, Mater. Sci. Eng. A 203 (1995) 1. M. Mabuchi, H. Iwasaki, K. Higashi, Acta Mater. 46 (1998) 5335.
Hot compressive deformation behavior of a eutectic Al–Si alloy based composite reinforced with ␣-Si3N4 whisker A.H. Feng, L. Geng∗ , J. Zhang, C.K. Yao School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China Received 15 May 2003; accepted 6 June 2003
Abstract Elevated temperature compressive deformation behavior of a 4032 aluminum alloy matrix composite reinforced with 20 vol.% ␣-Si3 N4 whisker was investigated at the strain rate from 0.016 to 1.0 s−1 . The deformation temperatures were below and above the solidus temperature of the composite, which was determined by differential scanning calorimeter (DSC). It was found that the flow stress of the composite decreased with increasing compressive temperature. The microstructure of the composite was observed and analyzed by using optical microscope (OM) and TEM. The morphology of eutectic Al–Si was found to plays an important role in the compressive deformation behavior of the composite. In addition, there are interfacial reactions between the matrix alloy and the Si3 N4 whiskers due to segregation of the alloy elements near the matrix/reinforcement interfaces. © 2003 Elsevier B.V. All rights reserved. Keywords: Deformation; DSC; TEM; Composite materials
1. Introduction
2. Experimental materials and procedures
Al–Si alloys have been widely used as aluminum casting alloys because of their attractive physical and mechanical properties, especially the Si microstructure as a function of growth conditions [1,2]. Extensive researches [3–8] have been carried out on the microstructures of the Al–Si alloys as a function of nucleation and growth conditions during the solidification process, but relatively little work has focused on the compressive deformation of the Si3 N4 w/Al–Si composites. Compressive deformation is a valuable way to study the plastic deformation of metal matrix composites. Based on the Al–Si phase diagram, the basic microstructure is primary aluminum solution and Al–Si eutectic phase for 4032 Al alloy. The morphology of eutectic Al–Si and primary aluminum solution play an important role in determining the mechanical properties of these alloys. The focus of this study is mainly on the compressive characteristics and the effect of eutectic Al–Si on the elevated temperature compressive deformation behavior of the ␣-Si3 N4 w/4032 Al composite.
The ␣-Si3 N4 w/4032 Al composite with 20% volume fraction of the reinforcement was fabricated by squeeze casting. The composition of the 4032 alloy is as follows: 11.5 wt.% Si, 0.8–1.3 wt.% Mg, 0.5–1.3 wt.% Cu, 0.5–1.3 wt.% Ni and balance Al. The reinforcement material is ␣-Si3 N4 whisker with an average length of 20 m. In the present investigation, the compressive deformation was carried out over a wide temperature range of 773–873 K, including the temperatures below and above the solidus temperature of the composite. The solidus temperature of the composite was determined by using differential scanning calorimeter (DSC). Compressive deformation behavior of the composite at elevated temperatures was studied on Gleeble1500 Thermal Simulator. The microstructure of the composite was observed and analyzed by using optical microscope (OM) and TEM.
∗ Corresponding author. E-mail address: [email protected] (L. Geng).
0254-0584/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0254-0584(03)00323-7
3. Results and discussion Fig. 1 shows the DSC analysis results indicating the melting points. The solidus temperature of the Si3 N4 w/4032 Al composite is 810 K and that of the 4032 Al alloy is 805 K. As seen in Fig. 1, two endothermic peaks were observed in each curve, corresponding to eutectic Al–Si peak and
A.H. Feng et al. / Materials Chemistry and Physics 82 (2003) 618–621
0.0
0
-0.5
-1
-1.0 -2 DSC/mW/mg
DSC/mW/mg
619
-3 -4
-2.0 -2.5
-5 -6 300
-1.5
-3.0 400
500
600
700
Temperature
-3.5 300
400
500
600
700
Temperature
Fig. 1. The DSC analysis results of the (a) 4032 Al alloy and (b) Si3 N4 w/4032 composites at 30 K min−1 heating rate.
primary aluminum solution peak, respectively. The first endothermic peak at lower temperature corresponds to the fusion of the eutectic Al–Si and the second endothermic peak at higher temperature refers to the fusion of the primary aluminum solution. The endothermic peak of the Si3 N4 w/4032 Al composite may be completed earlier than the 4032 Al
matrix. The possible reason is the more interfaces in the Si3 N4 w/4032 Al composite and the morphology of primary aluminum solution changed from dendrite-like to equiaxed due to the addition of Si3 N4 whisker. Microstructure of the Si3 N4 w/4032 Al composite and the 4032 Al matrix is shown in Fig. 2. The microstructure of
Fig. 2. The microstructure of the 4032 Al matrix composite and Si3 N4 w/4032 Al composite (a) the 4032 Al alloy before being compressed; (b) the 4032 Al alloy after being compressed (T =833 K, ε˙ = 0.37 s−1 ); (c) the Si3 N4 w/4032 composite before being compressed and (d) the Si3 N4 w/4032 composite after being compressed (T =773 K, ε˙ = 0.37 s−1 ).
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A.H. Feng et al. / Materials Chemistry and Physics 82 (2003) 618–621 90
Si3N4w/4032Al 4032Al
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Si3N4w/4032Al 4032Al
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50 40 30 20
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Fig. 3. The true stress–true strain curves of the Si3 N4 w/4032 Al composite and the 4032 Al alloy compressed with a strain rate of 0.37 s−1 at different temperatures (a) T =773 K; (b) T =813 K; (c) T =833 K and (d) T =853 K.
4032 Al alloy consist of primary aluminum solution dendrites and eutectic Al–Si. The eutectic Al–Si distribution along the Al grain boundaries, shows the salient microstructure features. It is clear that the addition of Si3 N4 whiskers leads to a refinement of eutectic Al–Si and primary aluminum solution dendrites. The addition of Si3 N4 whisker changes not only the morphology of primary aluminum solution from dendrite-like to equiaxed, but also the morphology of the eutectic Al–Si from netlike to particulate. From Fig. 2(b), when the 4032 Al alloy is compressed at temperature 833 K, partial melting was found to start at the grain boundaries, followed by an apparent decrease in the proportion of eutectic Al–Si phase. Meanwhile, the primary aluminum solution dendrite arms coarsened during hot compressed. Fig. 3 shows the true stress–true strain curves of the Si3 N4 w/4032Al composite and the 4032 Al alloy compressed with a strain rate of 0.37 s−1 at different temperatures. It can be seen that the flow stresses of the Si3 N4 w/4032 Al composite are much higher than that of the 4032 Al alloy at lower temperatures (773 and 813 K), but
the difference becomes quite small at higher temperatures (833 and 853 K). The strength of the composites decreased with increasing compressive temperature. When the composite is compressed at 833 K and above, the liquid phase, resulting from the melting of ternary Al–Si–Mg eutectic at 833 K, appears preferentially at reinforcement/matrix interface or the grain boundaries, resulting in a sharp decrease of load transfer ability of the interface and in turn an obvious decrease of the flow stress of the composite as shown in Fig. 3. When the composite is compressed at 833 K, a larger amount of liquid phase appears, resulting from the melting of binary Al–Si eutectic at 850 K, which does not contribute to large flow stress. This suggests that mechanism of deformation is strongly affected by the volume and distribution of a liquid phase. Microstructure of the compressed Si3 N4 w/4032 Al composites is also characterized by the interfacial reaction. The Si3 N4 whisker is very stable and the interfacial reactions are carried out by the interaction between an amorphous surface layer of the whisker and the segregated Mg atoms in the matrix, resulting in the formation of MgO, MgAl2 O4
A.H. Feng et al. / Materials Chemistry and Physics 82 (2003) 618–621
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Fig. 4. The interfaces of Si3 N4 w/4032 Al composite compressed at different parameters (a) ε˙ = 0.016 s−1 , 793 K; (b) ε˙ = 0.016 s−1 , 813 K and (c) ε˙ = 0.094 s−1 , 853 K.
particles at the interfaces [9]. The interfacial reaction becomes strong with increasing temperature due to segregation of solute atoms near the matrix/reinforcement interfaces as shown in Fig. 4.
Acknowledgements The authors are grateful for the finance support of the National Nature Science Foundation of People’s Republic of China under grant No. 50071018.
4. Conclusion References The microstructure of 4032 Al alloy consist of primary aluminum solution dendrites and Al–Si eutectic. The eutectic Al–Si distributed along the Al grain boundaries, showing the salient microstructure features. It is clear that the addition of Si3 N4 whiskers leads to a refinement of eutectic Al–Si and primary aluminum solution dendrites. The flow stress of the composites decreased with increasing compressive temperature. The morphology of eutectic Al–Si and primary aluminum solution play an important role in determining the compressive properties of these alloys. In addition, there was interfacial reaction between the matrix and Si3 N4 whiskers due to segregation of solute atoms near the matrix/reinforcement interfaces.
[1] [2] [3] [4] [5] [6] [7] [8] [9]
H. Akbulut, M. Durman, F. Yilmaz, Wear 215 (1998) 170. C.R. Ho, B. Cantor, Acta Metal. Mater. 43 (1994) 3231. J. Braszczynski, A. Zyska, Mater. Sci. Eng. A 278 (2000) 195. S. Nagarajan, B. Dutta, M.K. Surappa, Compos. Sci. Technol. 59 (1999) 897. R.-Y. Wang, W.-H. Lu, L.M. Hogan, J. Cryst. Growth 207 (1999) 43. M.O. Pekguleryuz, N. Pedneau, Scripta Mater. 38 (1998) 1533. M. Gupta, S. Ling, J. Alloys Compd. 287 (1999) 284. W.R. Loue, M. Suery, Mater. Sci. Eng. A 203 (1995) 1. M. Mabuchi, H. Iwasaki, K. Higashi, Acta Mater. 46 (1998) 5335.