New Semisolid Casting of an Al-25Wt.% Mg₂Si Composite Using Vibrating Cooling Slope

Abstract:

Al-Mg₂Si composites have gained considerable attention because of their attractive properties such as low density, improved wear resistance and good castability. However, when in-situ routes are used for processing of these composites, the formation of coarse Mg₂Si particles with sharp cornersis inevitable and is detrimental for the composite properties. This problem is intensified when a hypereutectic composition such as Al-25wt.% Mg₂Si alloy is processed. In the present study, an innovative semisolid technique termed as the Vibrating Cooling Slope (VCS) has been applied to produce a sample of in-situ Al-25wt.% Mg₂Si composite.This technique combines the conventional cooling slope and vibration casting methods into an integrated one for producing fine and globular structures in the as-cast condition. An inclined plate was prepared from a 10mm thickness copper plate and was coated by boron nitride. This platecould vibrate mechanically in the vertical direction at a predetermined frequency by the aid of four springs and an electric motor. The molten Al-16.5wt.%Mg-9.4%Sialloy with 100^o C superheat was poured on the surface of this cooling slope (set at 45° inclined angle)while it was vibrating at the frequency of 40 Hzandamplitude of 400 μm.The semisolid alloy travelled the length of 40 cm on the slope before being poured into a steel mold (60 mm internal diameter and 35 mm in height). Also for the purpose of comparison, gravity casting (GC) and conventionally still cooling slope casting (CS)were carried outboth using the same mold and with the same superheat.The samples were sectioned, polished and subjected to metallographicstudies,porosity and hardness measurements. It was concluded that CS and VCS techniques resulted in a decrease in the size of Mg₂Si particles by about 50%and 70% respectively when compared with the gravity casting. However, the increased shape factor of Mg₂Si particles in the VCS and CS processed samples was insignificant as compared with GC. Although in comparison with GC, the VCS processed sample showed a higher porosity level, it exhibited a higher hardness value. These results were attributed to the finer and modified microstructure obtained via this newly developed technique.

• Periodical: Solid State Phenomena (Volumes 217-218)
• Pages: 389-396
• DOI: https://doi.org/10.4028/www.scientific.net/SSP.217-218.389
• Online since: September 2014
• Authors: Shaya Saffari*, Farshad Akhlaghi
• Keywords: Al-Mg₂Si, Composite, Hardness, In Situ, Microstructure, Modification, Semi-Solid, Vibrating Cooling Slope

References

[1] C. Li, Y.Y. Wu, H. Li, X.F. Liu, Morphological evolution and growth mechanism of primary Mg2Si phase in Al–Mg2Si alloys, Acta Mater. 59 (2011) 1058–1067.

DOI: 10.1016/j.actamat.2010.10.036

[2] J. Zhang, Z. Fan, Y. Wang, B. Zhou, Hypereutectic aluminum alloy tubes with graded distribution of Mg2Si particles prepared by centrifugal casting, Mater. and Des. 21 (2000) 149-153.

DOI: 10.1016/s0261-3069(99)00100-4

[3] H.V. Atkinson, Modeling the semisolid processing of metallic alloys, Prog. Mater. Sci. 50 (2005) 341.

[4] Q.D. Qin, Y.G. Zhao, P.J. Cong, W. Zhou, B. Xu, Semisolid microstructure of Mg2Si/Al composite by cooling slope cast and its evolution during partial remelting process, Mater. Sci. Eng. A 444 (2007) 99–103.

DOI: 10.1016/j.msea.2006.08.074

[5] Q.D. Qin, Y.G. Zhao, K. Xiu, W. Zhou, Y.H. Liang, Microstructure evolution of in situ Mg2Si/Al–Si–Cu composite in semisolid remelting processing, Mater. Sci. Eng. A 407 (2005) 196–200.

DOI: 10.1016/j.msea.2005.07.021

[6] M. Azarbarmas, M. Emamy, M. karamouz, M. Alipour, J. Rassizadehghani, The effects of boron additions on the microstructure, hardness and tensile properties of in situ Al–15%Mg2Si composite, Mater. and Des. 32 (2011) 5049–5054.

DOI: 10.1016/j.matdes.2011.05.036

[7] Y.G. Zhao, Q.D. Qin, W. Zhou, Y.H. Liang, Microstructure of the Ce-modified in situ Mg2Si/Al–Si–Cu composite, J. of All. and Comp. 389 (2005) L1–L4.

DOI: 10.1016/j.jallcom.2004.08.003

[8] M.R. Ghorbani, M. Emamy, R. Khorshidi, J. Rasizadehghani, A.R. Emami, Effect of Mn addition on the microstructure and tensile properties of Al–15%Mg2Si composite, Mater. Sci. and Eng. A 550 (2012) 191-198.

DOI: 10.1016/j.msea.2012.04.056

[9] A. Malekan , M. Emamy, J. Rassizadehghani, A.R. Emami, The effect of solution temperature on the microstructure and tensile properties of Al–15%Mg2Si composite, Mater. and Des. 32 (2011) 2701–2709.

DOI: 10.1016/j.matdes.2011.01.020

[10] Z. Min, W. Hui-yuan, L. Bo, Z. Bing, L. Min-li, L. Dong, J. Qi-chuan, Influence of melt superheating on microstructures of Mg-3. 5Si-1Al alloys, Trans. Nonferrous Met. Soc. China 18 (2008) s107-s112.

DOI: 10.1016/s1003-6326(10)60184-7

[11] M. Mabuchi, K. Higashi, Strengthening mechanisms of Mg2Si alloys, Acta Mater. 44 (1996) 4611.

[12] G. Frommeyer, S. Beer, K. Von Oldenburg, Microstructure and mechanical properties of mechanically alloyed intermetallic Mg2Si-Al alloys, Z. Metall. 85 (1994) 372.

DOI: 10.1002/chin.199438008

[13] Y. Tsunekawa, H. Suzuki and Y. Genma, Application of ultrasonic vibration to in situ MMC process by electromagnetic melt stirring, Mater. and Des. 22 (2001) 467- 472.

DOI: 10.1016/s0261-3069(00)00079-0

[14] R.M. Pillai, K.S. Biju Kumar and B.C. Pai, A simple inexpensive technique for enhancing density and mechanical properties of Al-Si alloys, J. Mater. Proc. Technol. 146 (2004) 338–348.

DOI: 10.1016/j.jmatprotec.2003.11.022

[15] R.G. Guan, F.R. Cao, L.Q. Chen, J.P. Li, C. Wang, Dynamical solidification behaviors and microstructural evolution during vibrating wavelike sloping plate process, J. of Mater. Proc. Technol. 209 (2009) 2592–2601.

DOI: 10.1016/j.jmatprotec.2008.06.007

[16] S. Gencalp, N. Saklakoglu, Semisolid microstructure evolution during cooling slope casting under vibration of A380 aluminum alloy, Mater. and Man. Proc. 25 (2010) 943–947.

DOI: 10.1080/10426911003636944

[17] F. Akhlaghi, A. Taghani, Development of vibrating cooling slope (VCS) method for enhancing a globular structure in aluminum A356 alloy, Proc. of 12th Internat. Conf. on Aluminum Alloys, September 5-9, 2010, Yokohama, Japan The Japan Inst. of Light Met. (2010).

[18] H. Khosravi, F. Akhlaghi, A comparative study on the distribution of SiC particles within the matrix of Al-A356/SiCp composites processed via compocasting and vibrating cooling slope routes, Iranian Cast. Jour. 98 (2011) 2-8.

DOI: 10.1016/s1003-6326(15)63867-5

[19] Z. Fan, Y. Q. Wang, B. L. Zhou, Effect of cooling rate on the microstructure of hypereutectic Al-Mg2Si alloys, J. Mater. Sci. Lett. 19 (2000) 1825 –1828.