SIFAT FISIK DAN MEKANIK KOMPOSIT ALUMINIUM DIPERKUAT DENGAN KERAMIK ZIRCONIA YANG DIBUAT DENGAN METODE HOT EXTRUSION

MUHAMMAD BUDI NUR RAHMAN, Ir. M. Waziz Wildan, M.Sc, Ph.D; Dr. Ir. Subarmono, MT

2016 | Tesis | S2 Teknik Mesin

Aluminium banyak digunakan dalam dunia industri karena ringan, tangguh, tahan korosi, daya hantar listrik dan panas yang tinggi serta mudah dibentuk. Namun, aluminium memiliki kekurangan yaitu nilai kekerasan yang relatif rendah sehingga daya tahan ausnya juga rendah. Peningkatan kekuatan aluminium dapat dilakukan dengan Aluminum Matrix Composites (AMC) selain dengan paduan unsur yang lain. Pengaruh penambahan partikel zirconia (ZrO2) sebagai material penguat sifat fisik dan mekanik aluminium dalam pembuatan AMC yang dilakukan dengan metode hot extrusion perlu diteliti. Serbuk ZrO2 merupakan bahan keramik yang keras dan tahan suhu tinggi. Penambahan partikel ZrO2 sebanyak 0; 2,5; 5; 7,5, 10, 12,5 dan 15% fraksi berat dicampur dengan serbuk alumunium menggunakan turbula mixer selama 2 jam selanjutnya dikompaksi secara uniaksial dengan tekanan 300 MPa. Proses hot extrusion pada suhu 575, 600 dan 625°C dengan holding time 30 menit. Pengujian yang dilakukan adalah densitas relatif, kekerasan makro dan mikro Vickers, laju keausan, bending dan impak dilengkapi dengan pengamatan struktur mikro menggunakan scanning electron microscope (SEM) dan pengamatan struktur makro specimen menggunakan kamera SL300. Hasil pengujian menunjukkan bahwa peningkatan suhu ekstrusi dan penambahan fraksi berat ZrO2 meningkatkan densitas relatif dan nilai kekerasan komposit. Pada suhu ekstrusi 625°C densitas relatif berada pada interval 91-95 %, sedangkan nilai kekerasan pada interval 66-74 kg/mm2. Penambahan ZrO2 menurunkan laju keausan dan kekuatan bending sampai fraksi berat 5% dan selanjutnya relatif konstan. Nilai laju keausan dan kekuatan bending pada kondisi tersebut sebesar 0,029 mg/MPa.m dan 42,83 MPa sedangkan pada 0% ZrO2 sebesar 0,91 mg/MPa.m dan 48,57 MPa. Penambahan fraksi berat ZrO2 meningkatkan kekuatan impak sampai 7,5% sebesar 0,15 J/mm2 selanjutnya cenderung turun kembali. Hasil pengamatan SEM menunjukkan penambahan fraksi berat ZrO2 dapat mengurangi ukuran porous.

Due to its low density, high toughness, high corrosion resistance, high electrical and thermal conductivities, and ease of forming, aluminum has been being widely used in various industries. However, aluminum possesses considerably low hardness leading to low wear resistance is among its limitation. In addition to being alloyed with other elements, the strength of aluminum can be improved by producing aluminum matrix composites (AMC). The effect of zirconia (ZrO2) addition as reinforcing material on the physical and mechanical properties of aluminum by producing AMC using hot extrusion method has been investigated. ZrO2 particle possessing high hardness and high temperature resistance belongs to ceramic material. Various amounts of 0, 2.5, 5, 7.5, 10, 12.5 and 15% of weight of ZrO2 particle was mixed with aluminum particle in a tubular mixer for two hours, followed by uni-axial compaction at 300 MPa. Hot extrusion was conducted at various temperatures of 575, 600 and 625°C for 30 minute holding time. The properties being investigated include relative density, Vickers hardness, wear rate, flexural strength and impact toughness, as well as micro structure using SEM and macro structure of the specimens. It was revealed that relative density and hardness of the AMC increase with the increase of the temperature extrusion and the ZrO2 content. The relative density and the hardness of the AMC produced at 625°C temperature ranges from 91% to 95%, and from 66 kg/mm2 to 74 kg/mm2, respectively. The increase of ZrO2 content up to 5 wt% resulted in lowering wear rate and flexural strength, and further increase of the content did not show any considerable change in both wear rate and flexural strength. Whilst wear rate and flexural strength at 5 wt% of ZrO2 content were found being 0.029 mg/MPa.m and 42.83 MPa, respectively, those at 0 wt% of ZrO2 content were 0.91 mg/MPa.m and 49.57 MPa, respectively. The increase of ZrO2 content up to 7.5 wt% leads to an increase of impact toughness up to 0.15 J/mm2, while a decrease in impact toughness was observed for further increase of ZrO2 content. SEM images show that the higher the ZrO2 content, the smaller the size of the pores.

Kata Kunci : AMC, fraksi berat zirconia, hot extrusion