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Abstrak :
Komponen flens motor sungai hasil pengecoran cetakan pasir memperlihatkan kecenderungan mengalami kegagalan keausan. Selain itu kualitas maupun surface finish yang dihasilkan kurang baik. Metode pengecoran squeeze atau liquid metal forging dapat mengurangi porositas oleh karena pemberian tekanan selama proses pembekuan logam berlangsung. Menurut penelitian sebelumnya squeeze casting juga dapat memperbaiki sifat mekanik dari paduan aluminium. Penelitian ini mencoba merancang proses pengecoran squeeze paduan aluminium daur ulang yang ada dengan cara memvariasikan parameter tekanan squeeze, dan temperatur punch & die. Langkah proses squeeze casting meliputi pemanasan logam dan die dalam dua dapur induksi berbeda, dilanjutkan dengan penuangan logam cairan ke dalam die dan diteruskan dengan pemberian tekanan selama waktu tertentu. Setelah melakukan beberapa pengujian terhadap spesimen, hasil yang diperoleh menunjukkan bahwa nilai kekerasan spesimen hasil squeeze casting meningkat, surface finish menjadi lebih baik dan persentase porositas yang dihasilkan menurun secara signifikan dibandingkan dengan proses pengecoran cetakan pasir yang ada.

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It was found that the flanges component of the river boats which undergo sliding contact to the spindle and produced by sand casting process is subject to wear failure. In addition to the cast quality and surface finish of the product is not good, Squeeze casting, which is also known as liquid metal forging, could reduce the porosity by the pressure applied during solidification. Previous research shows that the process could improve the mechanical properties of the aluminum alloys casting. This research is to produce specimens by squeeze casting process using the existing recycled material by combining the process parameter such as squeeze pressure and punch & die temperature. The process consists of melting the alloys and heating the die in two difference resistance furnaces, ladling the melt into pre-heated die cavity and finally applying pressure by hydraulic power until the melt is fully solidified. After examining the specimens, the results shows the improvement in hardness, the improvement in surface finish and the significant decreasing in the quantity of the porosity as compared to traditional sand casting.

Abstrak :
Squeeze casting sering juga disebut dengan liquid metal forging, dimana logam cair dibekukan dibawah tekanan eksternal yang relatif tinggi. Terjadinya kontak antara logam cair dengan punch dan die pada saat penekanan memungkinkan terjadinya perpindahan panas yang cukup cepat. Ini akan menghasilkan struktur mikro yang lebih homogen serta perbaikan sifat mekanik, karena itu proses ini sangat baik digunakan untuk memproduksi komponen engineering yang membutuhkan kualitas tinggi. Material yang digunakan untuk pengujian ini diambil dari produk piston komersial lokal dengan komposisi bal. 12.62 wt% Si, 2.83 wt% Cu, 1.58 wt% Ni, 0.89 wt% Mg, 0.38 wt% Fe, 0.15 wt% Mn, 0.078 wt% Zn, 0.016 wt% Pb, 0,009 wt% Sn, 0.006 wL% Ca dan selebihnya Al, kemudian dilebur pada temperatur 4 00°C. Kemudiar, dibuat benda uji menggunakan teknik direct squeeze casting dengan jalan memvariasikan tekanan dan temperatur. Selanjutnya benda uji dikarakterisasi berupa kekerasan, porosity, struktur mikro dan kekasaran permukaan. Pada pengujian yang dilakukan, laju pendinginan material akibat pengaruh tekanan dan temperatur die sangat signifikan pengaruhnya terhadap perbaikan properties benda uji. Dari hasil pengamatan, proses ini mampu menurunkan porositas sampai 85.15 % dan memperbaiki kekerasan sebesar 5.29 % setelah dilakukan perlakukan panas T6. Tekanan serta temperatur die optimal didapatkan pada 70 - 100 MPa dan 400 - 450 °C. Squeeze casting which often known as liquid metal forging where molten metal is solidified under relatively high external pressure. Contact between molten metal and punch and die enable to increase the rate of heat tranfer. The microstructure of the casting will be more homogenous and the mechanical properties will be improved. Thus the process is very useful to produce high quality engineering components. The material used this investigation is taken from comercial piston product with the following composition bal.: 12.62 wt% Si, 2.83 wt% Cu, 1.58 wt% Ni, 0.89 wt% Mg, 0.38 wt% Fe, 0.15 wt% Mn, 0.078 wt% Zn, 0.016 wt% Pb, 0.009 wt% Sn, 0.006 wt% Ca and Al. The material was melted up to 700 °C, the specimens were made using direct squeeze casting by combining pressure and temperature. Finally the specimens were examined through hardness, porosity, microstructuere and surface roughness test as well. The results show the solidification rate significantly improves the properties of the specimen. The process decrease quantity of the porosity up to 85.15% and increase the Brinell hardness 5.29% after heat treated (T6). The optimum pressure and temperature is 70 - 100 MPa and 400 - 450 °C.

Abstrak :
ABSTRAK
Penutupan sumur secara permanen wajib dilakukan oleh seluruh Kontraktor Kontrak Kerja Sama KKKS pasca berhentinya produksi minyak dan gas bumi seiring dengan berakhirnya kontrak kerja wilayah dengan pemerintah. Penelitian ini berfokus pada pekerjaan squeeze cementing yang merupakan bagian dari operasi tahapan awal cement plug pertama 1 pada proyek plug and abandonment di PT XYZ. Metode yang digunakan dalam penelitian ini adalah dengan menghitung nilai factor injektivitas injectivity factor yang didapatkan dari studi lapangan sehingga menjadi factor kunci dalam menentukan tipe jenis semen yang akan digunakan pada pekerjaan squeeze cementing. Berdasarkan pengerjaan di lapangan terhadap 10 sumur pada PT XYZ, diperoleh hasil yang menunjukkan bahwa terdapat 8 sumur yang memiliki nilai factor injektivitas kurang dari 2000 2000 , sehingga jenis microfine cement digunakan untuk menutup zona formasi reservoir. Keberhasilan penggunaan microfine cement pada penelitian ini memberikan dampak terhadap berkurangnya pekerjaan ulang yang diakibatkan oleh kesalahan dalam pemilihan tipe material semen sebelum melakukan pekerjaan squeeze cementing. Hasil ini juga membantu pihak perusahaan untuk menghindari terjadinya penambahan biaya sebesar 9.3 yang diakibatkan karena kegagalan setiap kali pekerjaan penyemenan. Hasil akhir dari studi ini berupa decision tree yang dapat membantu para pengambil keputusan untuk menentukan tipe jenis semen untuk operasi squeeze cementing dalam pekerjaan plug and abandonment. Perbedaan alur kerja pada pohon keputusan yang baru dibandingkan dengan alur kerja sebelumnya adalah adanya tambahan proses pada tahap kalkulasi dan analisis nilai faktor injektivitas injectivity factor value untuk menentukan tipe jenis semen yang tepat sebelum dilakukan operasi squeeze cementing. Hasil studi ini diharapkan bisa dijadikan acuan oleh KKKS di Indonesia sehingga alokasi biaya/anggaran proyek plug and abandonment menjadi optimal.

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ABSTRACT
A permanent well abandonment shall be done by all Production Sharing Contract PSC company following the cessation of oil and gas production and in line with the expiration of the regional contract with the government. This study focuses on the work of squeeze cementing which is part of the initial stages operation of the first cement plug 1 on the plug and abandonment project in PT XYZ. The method used in this research is by calculating the value of the injectivity factor obtained from field study as a key factor in determining the type of cement that will be used in squeeze cementing operation. Based on on field execution on 10 wells at PT XYZ, the results show that there were 8 wells with injectivity factor values less than 2000 2000 injectivity values, so the type of microfine cement is used to close the reservoir formation zone. The successful use of microfine cement utilization in this study had an impact on reducing remedial job due to improper method in the selection of cement type materials prior to performing the squeeze cementing operation. These results also help the company to avoid the incremental cost of 9.3 for each failure of cementating job. The final result of this study is a decision tree that can assist decision makers to determine the type of cement for squeeze cementing operations in plug and abandonment operation. The differences between new developed decision tree compare to the previous workflow is the addition of processes at the calculation stage and the analysis of the injectivity factor value in order to determine type of cement prior to do squeeze cementing. The results of this study are expected to be used as a reference by KKKS in Indonesia so that the allocation of cost budget of the project plug and abandonment can be optimized.

Abstrak :
Baja sering digunakan sebagai material penyusun pada badan pelindung kendaraan taktis karena ketahanan balistiknya yang baik. Dengan densitasnya yang tinggi, memicu pengembangan material pengganti dengan densitas yang lebih rendah namun tetap dapat menahan penetrasi peluru. Salah satunya adalah komposit aluminium dengan penguat SiC. Pada penelitian sebelumnya, pelat komposit Al-6Mg-xZn dengan variasi 6, 9 wt.% Zn berpenguat 10 dan 20 vol.% SiC telah berhasil menahan peluru tipe III, namun masih mengalami retak dibagian belakang. Oleh karena itu, perlu adanya modifikasi matriks agar menghasilkan komposit yang lebih tangguh seperti penambahan Cr. Pada penelitian ini dipelajari komposit Al-11Zn-7Mg berpenguat 10 vol.% SiC dengan variasi kadar Cr sebesar 0, 0.043, 0.051, 0.083 wt.% yang difabrikasi melalui metode squeeze casting. Untuk meningkatkan sifat mekanis, pelat komposit kemudian diberikan laku pelarutan pada temperatur 450 oC selama 1 jam yang dilanjutkan dengan laku penuaan pada temperatur 130 oC selama 102 jam. Karakterisasi yang dilakukan pada pelat komposit yaitu pengujian komposisi kimia menggunakan Optical Emission Spectrometry (OES), analisis struktur mikro dengan mikroskop optik (OM), Scanning Electron Microscopy (SEM) dan Energy Dispersive X-Rays (EDX), perhitungan persentase porositas dan pengukuran Secondary Dendrite Arm Spacing (SDAS) menggunakan perangkat lunak Image Pro Plus, pengujian kekerasan Rockwell B, serta pengujian impak metode charpy. ......Steel has been used as the constituent material for body of tactical vehicle due to its high ballistic resistance. But, steel has high density that triggered developments of lighter materials with high hardness and high impact energy such as SiC strengthened aluminium composites. Previous research has shown that 10 and 20 vol.% SiC strengthened Al-6Mg-xZn with variation 6 and 9 wt.% Zn could withstand type III bullets, but cracks remained at the back of the plate. Therefore, matrix modification is needed in order to produce thougher aluminium composite such as addition of Cr. This research used Al-11Zn-7Mg as matrix and 10 vol.% SiC as reinforcement with variation of 0, 0.043, 0.051 and 0.083 wt.% Cr which are fabricated by squeeze casting method. To improve the mechanical properties, the composite plates were solution treated at 450°C for 1 hour then aged at 130 oC for 102 hours. The characterization consisted of chemical composition testing by using Optical Emission Spectrometry (OES), microstructure analysis by using Optical Microscope (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Rays (EDX), porosity calculation and Secondary Dendrite Arm Spacing (SDAS) measurement by using Image Pro Plus software, hardness testing by using Rockwell B and impact testing by using charpy method. The results showed that addition of Cr from 0 to 0.083 wt.% increased the hardness of composite from 58.8 to 61.8 HRB and decreased the impact values from 11290.4 to 10131.8 J/m2. The increase in hardness was due to solid solution strengthening of Cr in Al-Zn-Mg matrix as well as reduction of SDAS from 21.6 to 17.1 μm respectively from the addition 0.043 to 0.083 wt.% Cr. Ageing at 130°C significantly increased the hardness of the composites from 83.1 to 90.7 HRB, however, Cr did not give impact on the precipitation processes. Along with the increasing hardness, the impact properties decreased which indicated reduction of toughness.

Abstrak :
Proteksi armor merupakan faktor penting dalam militer dengan membantu menahan penetrasi dari peluru dan mencegah cedera atau bahkan kematian. Di era ini, mobilitas tank terbatas. Sebuah tank umumnya terbuat dari baja berkekuatan tinggi dengan berat 7,86 g/cm3. Itu membuat tank memiliki berat umumnya 35-80 ton. Berat yang besar tersebut membuat mobilitas tank menjadi terbatas. Oleh karena itu, RHA (rolled homogenous armour) perlu diganti dengan bahan antipeluru ringan lainnya. Material yang memenuhi kriteria tersebut adalah komposit matriks logam, khususnya matriks aluminium, karena memiliki densitas yang rendah, sifat mekanik yang tinggi dan ketahanan korosi yang baik. AA7075 adalah bahan yang cocok untuk digunakan dalam kendaraan tempur. AA7075 adalah salah satu paduan aluminium terkuat. Paduan ini akan diperkuat dengan tambahan TiC dengan variasi bobot 0,1%, 0,2%, dan 0,3%. Pada penelitian ini proses fabrikasi komposit dilakukan dengan metode squeeze casting. Pelat dibagi oleh proses perlakuan panas dan proses perlakuan non-panas. Hasilnya menunjukkan bahwa semua sampel dapat menahan penetrasi peluru dari uji balistik tipe II tetapi tidak untuk Tipe III. Sampel 0,2% TiC dengan tambahan perlakuan panas memiliki kinerja balistik yang lebih baik, kinerja balistik meningkat seiringnya penambahan penguat, sementara nilai penurunan hadir dari 0,2% menjadi 0,3%. perlakuan panas yang diberikan pada sampel meningkatkan kekerasan, ketangguhan impak, dan ketangguhan balistik. ......Armour Protection is a crucial factor in the military by helping holding penetration from bullets to prevent injury or even death. In this era, a tank's mobility is limited. Tanks are generally made of high strength steel with 7.86 g/cm3 .it made standard tanks weigh 35-80 tons. That made the tank's mobility limited. Thus RHA is needed to be replaced by other lightweight bulletproof materials for the tanks. The materials that meet these criteria are metal matrix composite, especially aluminium matrix, because of the low density, high mechanical properties and good corrosion resistance. AA7075 is a suitable material for use in a combat vehicle. AA7075 is one of the strongest aluminium alloys. This alloy will be reinforced with TiC with weight variations of 0.1%, 0.2%, and 0.3%. In this research, the composite fabrication process is by squeeze casting. The plates are divided by Heat treatment process and non-heat treatment process. The results show that all the samples could withstand bullet penetration from the type II ballistic test but not Type III. With 0.2% TiC HT has better ballistic performance, the ballistic performance is increased with more reinforcement added. While a decreased value is present from 0.2% to 0.3%. Heat treatment given to the sample increases the hardness, impact toughness, and ballistic toughness.

Abstrak :
ABSTRAK
Latar Belakang : Strategi terapi Artritis Reumatoid (AR) menggunakan strategi terapi untuk mencapai target sehingga membutuhkan suatu intrumen yang valid dan akurat dalam menilai aktivitas penyakit AR. Instrumen yang paling banyak digunakan adalah DAS28, yang dikembangkan dari DAS namun tidak melibatkan pemeriksaan pada persenidan kaki dan pergelangan kaki. Telah terdapat banyak kritikan mengenai akurasi DAS28 dalam mengklasifikasikan kondisi aktivitas penyakit AR, terutama bila suatu kondisi aktivitas penyakit aktif diklasifikasikan sebagai tidak aktif (negatif palsu) karena hal ini dapat menyebabkan terapi yang tidak optimal dan pada akhirnya menyebabkan terjadinya disabilitas. Perbedaan utama antara DAS28 dan DAS terletak pada eksklusi persendian kaki dan pergelangan kaki, karena itu suatu instrumen baru DAS28-squeeze telah diajukan. Instrumen ini memeriksa 28 sendi yang ada pada DAS28 ditambah dengan tes penekanan pada sendi metatarsofalangeal. Namun instrumen baru ini belum pernah divalidasi secara radiologis. Tujuan : Menilai nilai diagnostic DAS28 dan DAS28-squeeze. Metode : Studi potong menggunakan USG Power Doppler sebagai acuan untuk mengevaluasi nilai diagnostik DAS28 dan DAS28-squeeze. Studi ini menggunakan kriteria USG paling ketat untuk mendefinisikan kondisi aktivitas penyakit aktif, yaitu sinyal Doppler positif disertai dengan hipertrofi synovium sedang pada B-mode. Hasil : Lima puluh enam subyek dilakukan pemeriksaan DAS28, DAS28-squeeze dan USG Power Doppler. Terdapat 4 kasus negatif palsu pada DAS28 dan 1 kasus pada DAS28-squeeze. Sensitivitas DAS28 dan DAS28-squeeze untuk mendeteksi kondisi aktivitas penyakit aktif masing-masing sebesar 73.3% dan 93.3%. Spesifisitas masing-masing sebesar 36.6% dan 34.1%, dan likelihood ratio negatif sebesar 0.73 dan 0.19. Simpulan : Studi ini adalah studi pertama yang memvalidasi DAS28-squeeze secara radiologis. Nilai negatif palsu DAS28-squeeze lebih rendah daripada DAS28 dan memiliki sensitivitas dan likelihood ratio negatif yang lebih baik daripada DAS28 untuk menentukan kondisi aktivitas penyakit AR.

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ABSTRACT
Background : Rheumatoid Arthritis (RA) treatment is based on ?treat to target? strategy which requires a valid and accurate tool in assessing disease activity. The most widely used tool is DAS28, which was developed from DAS with the omission of ankle and foot joints. Misclassification of disease state in DAS28, most importantly when an active disease state misclassified as unactive could lead to undertreatment and subsequently to disability. The main difference between DAS28 and DAS is the exclusion of ankle and foot joints, thus DAS28- squeeze has been proposed. It comprises the same 28 joints in DAS28 added with squeeze test on both metatarsophalangeal joints. Objective : To assess the diagnostic values of DAS28 and DAS28-squeeze. Methods : This is a cross-sectional diagnostic study using Power Doppler sonography as a reference standard in evaluating the diagnostic value of DAS28 and DAS28-squeeze. Results : Over the study period, 56 subjects underwent diagnostic tests using DAS28, DAS28- squeeze and Power Doppler sonography. There were 4 false negative in DAS28 and 1 in DAS28-squeeze. The sensitivities of DAS28 and DAS28-squeeze to identify active disease using Power Doppler sonography as reference standard were 73.3% and 93.3% respectively. While the specificities were 36.6% and 34.1% respectively. Furthermore the negative likelihood ratio were 0.73 and 0.19 respectively. Conclusion : This study is the first to validate DAS28-squeeze using imaging techniques. DAS28-squeeze false negative rate is much lower than DAS28. DAS28-squeeze has better sensitivity and negative likelihood ratio than DAS28 in identifying RA active disease state.

Abstrak :
[Baja digunakan sebagai material penyusun pada badan pelindung kendaran taktis karena ketahanan balistiknya yang baik. Tetapi, densitasnya yang tinggi memicu dilakukannya penelitian material pengganti, salah satu alternatifnya adalah komposit aluminium dengan penguat ZrO2. Pada penelitian penulis sebelumnya, tiga lapis pelat komposit Al-13,1Zn-6,1Mg-6,7Si-1,4Cu – 7.5 vol.% ZrO2 dengan tebal masing-masing pelat 10 mm terbukti mampu untuk menahan penetrasi peluru pada pengujian balistik tipe III. Pada penelitian ini, dibuat komposit pelat tebal dengan ketebalan 25 mm dengan matriks Al-9Zn-6Mg-3Si berpenguat 5 vol.% ZrO2 dan variasi penambahan paduan mikro berupa 0,001 wt.% Sr, 0,1 wt.% Ti, dan 2 wt.% Cr yang difabrikasi melalui metode squeeze casting. Untuk meningkatkan sifat mekanis, dilakukan laku pelarutan pada temperatur 450 oC selama 1 jam yang dilanjutkan dengan laku penuaan pada temperatur 200 oC selama 1 jam. Beberapa karakterisasi yang dilakukan adalah pengujian komposisi kimia menggunakan Optical Emission Spectrometer (OES), analisis struktur mikro dengan mikroskop optik (OM), Scanning Elecron Microscopy (SEM), dan Energy Dispersive X-Rays (EDX), perhitungan persentase porositas menggunakan perangkat lunak ImageJ, pengujian kekerasan Rockwell B, serta pengujian impak metode charpy. Pengujian balistik tipe III dilakukan pada pelat komposit setelah diberi perlakuan permukaan berupa thermal spray High Velocity Oxygen-Fuel (HVOF) menggunakan material pelapis 88WC-12Co dengan ketebalan ±200 μm. Hasil penelitian menunjukkan bahwa nilai kekerasan yang paling tinggi dimiliki oleh pelat komposit dengan paduan mikro Cr, yaitu mencapai 77,75 HRB. Pelat komposit dengan paduan mikro Ti memiliki harga impak yang paling tinggi yaitu mencapai 15,77 x 10-3 J/mm2. Seluruh pelat komposit memiliki nilai kekerasan yang relatif rendah bila dibandingkan dengan kekerasan teoritisnya, yang terjadi akibat proses fabrikasi yang tidak sempurna. Partikel ZrO2 yang ditambahkan pada lelehan paduan aluminium bereaksi sehingga membentuk Al3Zr yang ditemukan dalam jumlah yang banyak di dalam mikrostruktur komposit. Pada hasil pengujian balistik, pelat komposit Sr memiliki karakteristik balistik yang paling baik, yang terlihat dari jejak peluru pada bagian depan pelat dan diameter terperforasi pada bagian belakang pelat yang relatif kecil. Karakteristik balistik yang relatif baik ini didapatkan dari kombinasi nilai kekerasan dan harga impaknya yang relatif tinggi, yaitu 62,6 HRB dan 14,65 x 10-3 J/mm2 secara berurutan.;Steel has been used as the constituent material of tactical vehicle’s body due to its high ballistic resistance. But, steel has high density that triggered research for material substitution. One alternative is aluminium composite that reinforced by ZrO2. Previous research has shown that three plies of Al-13.1Zn-6.1Mg-6.7Si-1.4Cu – 7.5 vol.% ZrO2 composite, each with the thickness of 10 mm, could withstand bullet penetration on type III ballistic testing. In this research, Al-9Zn-6Mg-3Si composite thick plates of 25 mm reinforced by 5 vol.% ZrO2 with the variation of 0.001 wt.% Sr, 0.1 wt.% Ti, and 2 wt.% Cr microalloying are fabricated by squeeze casting method. To improve the mechanical properties, the composite plates were solution treated at 450 oC for 1 hour then aged at 200 oC for 1 hour. The characterizations are consisted of chemical composition testing by using Optical Emission Spectrometer (OES), microtructure analysis by using Optical Microscope (OM), Scanning Elecron Microscopy (SEM), and Energy Dispersive X-Rays (EDX), porosity calculation by using ImageJ software, hardness testing by using Rockwell B, and impact testing by using charpy method. Type III ballistic testing was conducted on the composite plates after High Velocity Oxygen-Fuel (HVOF) thermal spray with 88WC-12Co of ±200 μm thickness. The results showed that the highest hardness was owned by the Cr-added composite plate with the value of 77.75 HRB. The Ti-added composite plate had the highest impact value of 15.77 x 10-3 J/mm2. The hardness of all composite plates was relatively low compared to the theoritical hardness, which was due to imperfect fabrication process. The ZrO2 particles added to the molten aluminium alloy reacted to form Al3Zr, which was found in a considerable amount in the microstructure. From the ballistic testing, Sr composite plate was found to have the best ballistic characteristic compared to the other three, which was shown by small trace of bullet on the front part of the plate, and also small perforated diameter on the back part of the plate. This relatively good ballistic characteristic was believed to be due to combination of high hardness and impact values, with the value of 62.6 HRB and 14.65 x 10-3 J/mm2, respectively., Steel has been used as the constituent material of tactical vehicle’s body due to its high ballistic resistance. But, steel has high density that triggered research for material substitution. One alternative is aluminium composite that reinforced by ZrO2. Previous research has shown that three plies of Al-13.1Zn-6.1Mg-6.7Si-1.4Cu – 7.5 vol.% ZrO2 composite, each with the thickness of 10 mm, could withstand bullet penetration on type III ballistic testing. In this research, Al-9Zn-6Mg-3Si composite thick plates of 25 mm reinforced by 5 vol.% ZrO2 with the variation of 0.001 wt.% Sr, 0.1 wt.% Ti, and 2 wt.% Cr microalloying are fabricated by squeeze casting method. To improve the mechanical properties, the composite plates were solution treated at 450 oC for 1 hour then aged at 200 oC for 1 hour. The characterizations are consisted of chemical composition testing by using Optical Emission Spectrometer (OES), microtructure analysis by using Optical Microscope (OM), Scanning Elecron Microscopy (SEM), and Energy Dispersive X-Rays (EDX), porosity calculation by using ImageJ software, hardness testing by using Rockwell B, and impact testing by using charpy method. Type III ballistic testing was conducted on the composite plates after High Velocity Oxygen-Fuel (HVOF) thermal spray with 88WC-12Co of ±200 μm thickness. The results showed that the highest hardness was owned by the Cr-added composite plate with the value of 77.75 HRB. The Ti-added composite plate had the highest impact value of 15.77 x 10-3 J/mm2. The hardness of all composite plates was relatively low compared to the theoritical hardness, which was due to imperfect fabrication process. The ZrO2 particles added to the molten aluminium alloy reacted to form Al3Zr, which was found in a considerable amount in the microstructure. From the ballistic testing, Sr composite plate was found to have the best ballistic characteristic compared to the other three, which was shown by small trace of bullet on the front part of the plate, and also small perforated diameter on the back part of the plate. This relatively good ballistic characteristic was believed to be due to combination of high hardness and impact values, with the value of 62.6 HRB and 14.65 x 10-3 J/mm2, respectively.]

Abstrak :
[ABSTRAK
Pengelasan merupakan metode yang sering digunakan pada proses manufaktur dari kendaraan taktis. Pengelasan dengan menggunakan metode gas metal arc welding(GMAW) umum dilakukan pada paduan aluminium, dikarenakan minimnya kontaminasi dari udara dan memiliki kecepatan pengelasan yang tinggi karena elektroda terumpan secara kontinyu. Pada penelitian ini dilakukan pengelasan dengan metode GMAW pada pelat komposit Al-10Zn-6Mg-3Si yang diperkuat oleh 10 %Vol. SiC dengan menggunakan metode squeeze casting. Parameter yang digunakan adalah arus, yaitu sebesar 180, 210, dan 240 A, dengan variabel tetap tegangan sebesar 22 V, dan kecepatan pengelasan sebesar 180 mm/menit. Didapatkan variasi heat input sebesar 1.32, 1.54, dan 1.76 kJ/mm. Pengujian yang dilakukan antara lain uji tekuk, uji keras, SEM, dan metalografi. Hasil yang didapatkan adalah dengan penambahan heat input pada proses pengelasan, kekerasan yang didapatkan semakin menurun karena dengan penambahan heat input akan memperlambat pendinginan sehingga memperbesar butir.Ditemukan fasa Al4C3 pada pengujian SEM, yang mengakibatkan penurunan kekuatan dari produk pengelasan. Fasa tersebut didapatkan dari reaksi Al dengan SiC pada temperatur diatas 700oC, sedangkan temperatur pengelasan mencapai 2000o C.

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ABSTRACT
Welding is one of the most common method used in joining ballistic vehicle body structure. Welding with gas metal arc welding (GMAW) is widely used for joining aluminium alloy because of its low atmosphere contamination and continously feeding electrode that results in high welding velocity This research studied GMAW of Al-10Zn-6Mg-3Sicomposite reinforced by 10 %vol. SiC, produced by squeeze casting method. In GMAW, the current is varied to 180, 210, and 240 A, with constant voltage and velocity of 22 V and 180mm/min, respectively. Therefore heat input used in this research is varied to 1.32, 1.54, 1.76 kJ/mm. The characterization included bending test, microhardness test, dan metallography observation. The result shows that the higher heat input will decrease the hardness because it slowed down the cooling rate so that increased the grain size. Al4C3 was found on SEM observation, which decreased the strength of the weld products. Al4C3 was produced by the reaction of Al with SiC at 700 oC, which was lower than the welding temperature that exceed 2000 oC.;Welding is one of the most common method used in joining ballistic vehicle body structure. Welding with gas metal arc welding (GMAW) is widely used for joining aluminium alloy because of its low atmosphere contamination and continously feeding electrode that results in high welding velocity This research studied GMAW of Al-10Zn-6Mg-3Sicomposite reinforced by 10 %vol. SiC, produced by squeeze casting method. In GMAW, the current is varied to 180, 210, and 240 A, with constant voltage and velocity of 22 V and 180mm/min, respectively. Therefore heat input used in this research is varied to 1.32, 1.54, 1.76 kJ/mm. The characterization included bending test, microhardness test, dan metallography observation. The result shows that the higher heat input will decrease the hardness because it slowed down the cooling rate so that increased the grain size. Al4C3 was found on SEM observation, which decreased the strength of the weld products. Al4C3 was produced by the reaction of Al with SiC at 700 oC, which was lower than the welding temperature that exceed 2000 oC., Welding is one of the most common method used in joining ballistic vehicle body structure. Welding with gas metal arc welding (GMAW) is widely used for joining aluminium alloy because of its low atmosphere contamination and continously feeding electrode that results in high welding velocity This research studied GMAW of Al-10Zn-6Mg-3Sicomposite reinforced by 10 %vol. SiC, produced by squeeze casting method. In GMAW, the current is varied to 180, 210, and 240 A, with constant voltage and velocity of 22 V and 180mm/min, respectively. Therefore heat input used in this research is varied to 1.32, 1.54, 1.76 kJ/mm. The characterization included bending test, microhardness test, dan metallography observation. The result shows that the higher heat input will decrease the hardness because it slowed down the cooling rate so that increased the grain size. Al4C3 was found on SEM observation, which decreased the strength of the weld products. Al4C3 was produced by the reaction of Al with SiC at 700 oC, which was lower than the welding temperature that exceed 2000 oC.]

Abstrak :
[Stainless steel merupakan material yang paling banyak digunakan dalam pembuatan turbin pembangkit tenaga listrik Organic Rankine Cycle (ORC), karena densitasnya yang tinggi, membuat kinerja turbin menjadi kurang efisien. Salah satu alternatif penggantinya adalah paduan aluminium seri 7xx.x (Al-Zn-Mg) yang memiliki sifat mekanik terbaik dibandingkan dengan seri yang lainnya. Sifat mekanik paduan tersebut dapat ditingkatkan dengan penambahan Cr serta perlakuan pengerasan penuaan. Pada penelitian ini dipelajari pengaruh penambahan Cr sebesar 0, 0.03, 0.1 dan 0.46 wt. % pada paduan Al-10Zn-6Mg. Paduan dibuat dengan proses squeeze casting dengan tekanan sebesar 76 MPa. Pelat selanjutnya dihomogenisasi pada temperatur 400 oC selama 4 jam dan dilakukan proses pengerasan penuaan dengan melakukan solution treatment pada temperatur 440 oC selama 2 jam, pendinginan cepat, dan penuaan pada temperatur 130 oC. Karakterisasi yang dilakukan diantaranya adalah pengujian kekerasan Rockwell B, pengujian impak, pengamatan struktur mikro dengan mikroskop optik dan Scanning Electron Microscope (SEM) dilengkapi dengan Energy Dispersive X-Rays (EDX), dan Simultaneous Thermal Analysis (STA). Hasil penelitian menunjukkan bahwa penambahan Cr sebesar 0.03, 0.1 dan 0.46 wt. % meningkatkan kekerasan paduan Al-10Zn-6Mg menjadi 50.9, 52.8, 53.2 HRB yang diakibatkan oleh pengecilan ukuran SDAS, pembentukan larutan padar Cr di dalam matriks serta pembentukan fasa kedua (CrFe)Al7 dan CrAl7 pada penambahan 0.46 wt. % Cr. Penambahan Cr belum memberikan pengaruh yang signifikan terhadap proses pemanasan. ......Stainless steel is most widely used in manufacturing of turbine impeller of Organic Rankine Cycle (ORC). However, due to its high density, the performance of turbine becomes less efficient. One alternative to substitute stainless steel is 7xx.x series aluminum alloys (Al-Zn-Mg) which have good mechanical properties compared to other series. Their mechanical properties can be improved by the addition of Cr as well as precipitation hardening process. This research studied the effect of addition of Cr with variation of 0, 0.03, 0.1 and 0.46 wt. % in Al-10Zn-6Mg alloys. The samples were made by squeeze casting process with pressure of 76 MPa. The plate was then homogenized at 400 ° C for 4 hours, followed by precipitation hardening process which consisted of solution treatment at 440 ° C for 2 hours, water quenching and ageing 130 ° C. Characterization was done by Rockwell B hardness testing, impact testing, microstructure observation by using optical microscope and Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-rays (EDX) and Simultaneous Thermal Analysis (STA). The results showed that addition of Cr 0.03, 0.1 and 0.46 wt. % increase the hardness of Al-10Zn-6Mg aloys to 50.9, 52.8, 53.2 HRB respectively, which were due to reduction of SDAS, solid solution strengthening of Cr in the matrix and the formation of (CrFe)Al7 and CrAl7 second phases when 0.46 wt. % Cr was added. During ageing process also increased hardness alloys, but Cr were not have a significant impact on the transformation phase. The addition of Cr not have a significant influence on the heating process. ;Stainless steel is most widely used in manufacturing of turbine impeller of Organic Rankine Cycle (ORC). However, due to its high density, the performance of turbine becomes less efficient. One alternative to substitute stainless steel is 7xx.x series aluminum alloys (Al-Zn-Mg) which have good mechanical properties compared to other series. Their mechanical properties can be improved by the addition of Cr as well as precipitation hardening process. This research studied the effect of addition of Cr with variation of 0, 0.03, 0.1 and 0.46 wt. % in Al-10Zn-6Mg alloys. The samples were made by squeeze casting process with pressure of 76 MPa. The plate was then homogenized at 400 ° C for 4 hours, followed by precipitation hardening process which consisted of solution treatment at 440 ° C for 2 hours, water quenching and ageing 130 ° C. Characterization was done by Rockwell B hardness testing, impact testing, microstructure observation by using optical microscope and Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-rays (EDX) and Simultaneous Thermal Analysis (STA). The results showed that addition of Cr 0.03, 0.1 and 0.46 wt. % increase the hardness of Al-10Zn-6Mg aloys to 50.9, 52.8, 53.2 HRB respectively, which were due to reduction of SDAS, solid solution strengthening of Cr in the matrix and the formation of (CrFe)Al7 and CrAl7 second phases when 0.46 wt. % Cr was added. During ageing process also increased hardness alloys, but Cr were not have a significant impact on the transformation phase. The addition of Cr not have a significant influence on the heating process. , Stainless steel is most widely used in manufacturing of turbine impeller of Organic Rankine Cycle (ORC). However, due to its high density, the performance of turbine becomes less efficient. One alternative to substitute stainless steel is 7xx.x series aluminum alloys (Al-Zn-Mg) which have good mechanical properties compared to other series. Their mechanical properties can be improved by the addition of Cr as well as precipitation hardening process. This research studied the effect of addition of Cr with variation of 0, 0.03, 0.1 and 0.46 wt. % in Al-10Zn-6Mg alloys. The samples were made by squeeze casting process with pressure of 76 MPa. The plate was then homogenized at 400 ° C for 4 hours, followed by precipitation hardening process which consisted of solution treatment at 440 ° C for 2 hours, water quenching and ageing 130 ° C. Characterization was done by Rockwell B hardness testing, impact testing, microstructure observation by using optical microscope and Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-rays (EDX) and Simultaneous Thermal Analysis (STA). The results showed that addition of Cr 0.03, 0.1 and 0.46 wt. % increase the hardness of Al-10Zn-6Mg aloys to 50.9, 52.8, 53.2 HRB respectively, which were due to reduction of SDAS, solid solution strengthening of Cr in the matrix and the formation of (CrFe)Al7 and CrAl7 second phases when 0.46 wt. % Cr was added. During ageing process also increased hardness alloys, but Cr were not have a significant impact on the transformation phase. The addition of Cr not have a significant influence on the heating process. ]

Abstrak :
Aluminium dan paduannya tengah dikembangkan sebagai badan pesawat terbang karena sifatnya yang lebih ringan daripada baja dan mudah dibentuk. Paduan aluminium 7XXX yang mengandung Zn dan Mg dapat ditingkatkan sifat mekanisnya melalui proses deformasi. Persentase deformasi yang diberikan akan meningkatkan kekerasan paduan melalui mekanisme penguatan regang. Proses anil yang dilakukan setelah deformasi akan mengembalikan keuletan paduan melalui mekanisme stress relieve, rekristalisasi dan pertumbuhan butir. Penelitian ini bertujuan untuk mengetahui pengaruh persen deformasi dan temperatur anil terhadap rekristalisasi dan sifat mekanik paduan Al-4.7Zn-1.8Mg berat. Pembuatan paduan dilakukan dengan proses squeeze casting. Proses homogenisasi dilakukan pada temperatur 400 oC selama 4 jam. Paduan hasil homogenisasi kemudian diberikan canai dingin dengan persen deformasi 5, 10 dan 20 . Selanjutnya paduan dengan deformasi 20 diberi perlakuan panas anil dengan temperatur 300, 400 dan 500 oC selama 2 jam. Karakterisasi meliputi pengujian kekerasan untuk melihat pengaruh canai dingin dan temperatur anil terhadap sifat mekanik paduan, pengamatan struktur mikro dengan mikroskop optik dan Scanning Electron Microscope SEM yang dilengkapi dengan Energy Dispersive Spectroscopy EDS. Hasil penelitian menunjukkan bahwa peningkatan persen deformasi sebesar menyebabkan terjadinya pemipihan butir. Deformasi 5, 10 dan 20 menghasilkan rasio deformasi butir sebesar 2.19, 3.19 and 4.59 dan meningkatkan kerasan paduan dari 69.5 HV menjadi sebesar 95.3, 100.1 dan 105.4 HV. Perlakuan panas anil pada temperatur 300 oC menyebabkan terjadinya recovery sedangkan rekristalisasi terjadi pada temperatur 400 oC dgrain 290 ?m. Grain growth terjadi pada temperatur 500 oC dgrain 434 ?m yang menyebabkan penurunan kekerasand dari 105.4 HV menjadi 71.5, 96.8 and 95.3 HV berturut turut. Rekristalisasi sempurna diprediksi pada temperature anil 375 ndash; 425 oC selama 2 jam.

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Aluminium alloys are developed as airplane body due to its lighter weight compared to steel and good formability. Aluminium 7XXX series with Zn and Mg alloying elements are commonly used because of its mechanical properties can be improved through deformation process. Deformation such as cold rolling may increase the hardness of an alloy through strain hardening. Annealing process after deformation process will recover ductility through stress relieve, recrystallization and grain growth mechanisms. This research aimed to find out the effect of cold rolling and annealing temperatur on the recrystallization and mechanical properties of Al 4.7Zn 1.8Mg wt. alloy. The alloy was produced by squeeze casting process. Homogenization was conducted at 400 oC for 4 hours followed by cold rolling with degree of deformation of 5, 10 and 20 . The samples with 20 of deformation were then annealed at 300, 400 and 500 oC for 2 h. Vickers hardness test was performed on the cold rolled and annealed samples to reveal strain hardening effect and subsequent recrystallization process. Microstructure was observed by using optical microscope and Scanning Electron Microscope SEM with Energy Dispersive Spectroscopy EDS. The results showed that the higher the deformation, the more elongated the grains. Deformation of 5, 10 and 20 led to grain shape ratios of 2.19, 3.19 and 4.59, respectively and increase in the hardness of the alloy from 69.5 HV to 95.3, 100.1 and 105.4 HV, respectively. Annealing at 300 oC resulted in recovery, while at 400 oC, recrystallization occured dgrain 290 m. Grain growth was observed after annealing at 500 oC for 2 h dgrain 434 m. The annealing temperature of 300, 400 and 500 oC decrease the hardness of the alloy from 105.4 HV to 71.5, 96.8 and 95.3 HV, respectively. Full recrystallization was predicted to happen at 375 ndash 425 oC for 2 hours.