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

Diserahkan: 15 Januari 2013/Diterima: 3 September 2013

ABSTRAK

Pembentukan-tikso merupakan teknologi baharu untuk menghasilkan produk hampir siap yang dijalankan 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 dari 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 aluminium 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 weight percentage 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

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*Pengarang untuk surat-menyurat; email: shukor@utem.edu.my