Sains Malaysiana 43(5)(2014): 791–798

Permodelan Termodinamik Aloi Al-Si-Cu untuk Pemprosesan Logam Separa Pepejal

(Thermodynamic Modelling of Al-Si-Cu Alloys for Semisolid Metal Processsing)

M.S. SALLEH*^{1 2}, M.Z. OMAR¹, J. SYARIF¹& M.N. MOHAMMED¹

¹Jabatan Kejuruteraan Mekanik dan Bahan, Fakulti Kejuruteraan dan Alam Bina

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

²Jabatan Kejuruteraan Proses Pembuatan, Fakulti Kejuruteraan Pembuatan

Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka

Malaysia

Received: 15 January 2013/Accepted: 3 September 2013

ABSTRAK

Pembentukan-tikso merupakan teknologi baharu untuk menghasilkan produk hampir siap dalam keadaan separa pepejal. Proses ini dapat mengurangkan makropengasingan, keliangan serta memerlukan daya pembentukan yang rendah. Sehingga kini, terdapat beberapa aloi aluminium seperti gred A319, A356 dan A357 digunakan untuk pemprosesan logam separa pepejal. Oleh itu, terdapat permintaan untuk mempelbagaikan aloi aluminium daripada gred yang lain untuk pemprosesan logam separa pepejal. Kajian ini membincangkan tentang permodelan termodinamik untuk meramal perubahan sifat aloi aluminium gred A319 apabila kandungan elemen pengaloian seperti tembaga, mangan dan ferum dipelbagaikan agar memenuhi kriteria pemprosesan logam separa pepejal. Kesemua pengiraan dalam kerja permodelan ini menggunakan perisian komersial 'Java-based Material Properties' (JMatPro). Pengiraan termodinamik berdasarkan persamaan 'Scheil' digunakan untuk menentukan julat suhu pemejalan (ΔT), kepekaan pecahan cecair (dfL/dT) dan suhu tingkap pemprosesan (ΔT30/50). Daripada pengiraan termodinamik, didapati suhu pemejalan aloi yang telah ditingkatkan %bt kandungan tembaga, mangan dan ferum menurun daripada 130 kepada 113°C manakala suhu eutektik meningkat daripada 510 kepada 515°C. Kepekaan pecahan cecair pula berkurangan daripada 0.017 kepada 0.007°C-1 manakala suhu tingkap pemprosesan menurun daripada 26 kepada 24°C. Tindak balas perduaan eutektik pula berlaku antara 30 dan 50% pecahan cecair untuk kesemua kumpulan aloi. Gambarajah fasa digunakan untuk mengetahui fasa sebatian antara logam seperti β-Al5FeSi dan Al2Cu yang terbentuk dalam aloi tersebut. Hasil daripada permodelan termodinamik ini menunjukkan kesesuaian aloi yang dipelbagaikan % bt elemen tembaga, mangan dan ferum digunakan untuk pemprosesan logam separa pepejal.

Kata kunci: Julat suhu pemejalan; kepekaan pecahan cecair; pembentukan-tikso; pengiraan termodinamik; suhu tingkap pemprosesan

ABSTRACT

Thixoforming is a new technology in producing near net-shape products in semisolid state. This process can reduce macrosegregation, porosity and involve low forming forces. Currently, there are a few grades of aluminum alloys such as A319, A356 and A357 commonly used in semi-solid metal processing. Therefore, there is a demand to widen the range of aluminum alloys specially tailored for semisolid metal processing. This study discusses the thermodynamic modelling to predict changes in the properties of aluminum alloy A319 expecially when the content of alloying elements such as copper, manganese and iron are varied in order to fulfill the criteria of semisolid metal processing. All the calculations in the present work were performed using Java-based Material Properties (JMatPro) commercial software. Thermodynamic calculation based on Scheil's equation is used to determine solidification temperature range (ΔT), liquid fraction sensitivity (dfL/dT) and processing window temperature (ΔT30/50). The thermodynamic calculation shows that the solidification temperatures have decreased from 130 to 113°C while the eutectic temperatures have increased from 510 to 515°C when the wt.% of copper, manganese and ferum were increased. The liquid fraction sensitivity is reduced from 0.017 to 0.007°C-1 and the processing window temperature is reduced from 26 to 24°C. Eutectics binary reactions occurred between 30 and 50% liquid fraction for all alloy groups. Phase diagram is used to identify the formation of intermetallic phase compound such as β-Al5FeSi and Al2Cu in the alloys. The results indicate the suitability of these modified alloys as potential materials for semisolid processing.

Keywords: Liquid fraction sensitivity; processing window temperature; solidification temperature range; thermodynamic calculation; thixoforming

REFERENCES

Birol, Y. 2007. A357 thixoforming feedstock produced by cooling slope casting. Journal of Materials Processing Technology 186: 94-101.

Chang, K., Liu, S., Zhao, D., Du, Y., Zhou, L. & Chen, L. 2011. Thermodynamic description of the Al-Cu-Mg-Mn-Si quinary system and its application to solidification simulation. Thermochimica Acta 512: 258-267.

Camacho, A.M., Atkinson, H.V., Kapranos, P. & Argent, B.B. 2003. Thermodynamic predictions of wrought alloy compositions amenable to semi-solid processing. Acta Materialia 51: 2319-2330.

Fredriksson, H. & Akerlind, U. 2012. Solidification and Crystallization Processing in Metals and Alloys. New York: John Wiley & Sons Ltd.

Han, Q. & Viswanathan, S. 2004. The use of thermodynamic simulation for the selection of hypoeutectic aluminium-silicon alloys for semisolid metal processing. Materials Science and Engineering A 364: 48-54.

Liu, D., Atkinson, H.V. & Jones, H. 2005. Thermodynamic prediction of thixoformability in alloys based on the Al-Si-Cu and Al-Si-Cu-Mg systems. Acta Materialia 53: 3807-3819.

Modigell, M. & Koke, J. 2001. Rheological modelling on semi-solid alloys and simulation of thixocasting processes. Journal of Materials Processing Technology 111: 53-58.

Omar, M.Z., Atkinson, P. & Kapranos, P. 2011. Thixotropy in semisolid steel slurries under rapid compression. Metallurgical and Material Transaction A 42: 2807-2819.

Patel, J.B., Liu Y.Q., Shao, G. & Fan, Z. 2008. Rheo-processing of an alloy specifically designed for semisolid metal processing based on the Al-Mg-Si system. Material Science Engineering A 476: 341-349.

Salleh, M.S., Omar, M.Z., Syarif, J. & Mohammed, M.N. 2013. Thermodynamic simulation on thixoformability of aluminium alloys for semi-solid processing. International Journal of Mathematics and Computers in Simulation 7: 286-293.

Tzimas, E. & Zavaliangos, A. 1999. Materials selection for semisolid processing. Materials and Manufacturing Processes 14(2): 217-230.

Yuan-dong, L., Apelian, D., Bo, X., Ying, M. & Yuan, H. 2010. Commercial AM60 alloy for semisolid processing: Alloy optimization and thermodynamic analysis. Transactions of Nonferrous Metals Society of China 20: 1572-1578.

*Corresponding author; email: shukor@utem.edu.my