Karakterisasi Hydrogen Induced Cracking pada Blahan AA5083 H116 di Las Metal Inert Gas dengan Kedalaman Takik 0.5 mm Selama 5 Minggu di Lingkungan 3.5% wt NaCl

DWI ERLIANTO, Ir. Mudjijana, M.Eng.

2017 | Skripsi | S1 TEKNIK MESIN

Hydrogen induced cracking merupakan suatu peristiwa retaknya material akibat dari masuknya atom hidrogen dan memenuhi batas butir material dalam jumlah yang besar. Peristiwa seperti ini biasanya disebut juga dengan istilah penggetasan hidrogen. Tujuan dari penelitian ini adalah untuk mengkarakterisasi hydrogen induced cracking pada bahan AA 5083 H116 di lingkungan 3,5 % wt NaCl. Penelitian ini menggunakan alat uji bending sesuai dengan skema Brown dan Beachem serta ASTM E 1681. Spesimen yang digunakan pada pengujian ini dibuat sesuai dengan benda uji yang diberi takik dengan electro discharge machining (EDM) pada weld metal dan heat affected zone (HAZ) sampel IZOD ( ASTM E 23 ). Untuk mencapai tujuan dalam penelitian ini dilakukan pembebanan statis pada 4 spesimen dengan beban sebesar 40 N selama 5 minggu. Untuk mempercepat proses penggetasan spesimen direndam dalam cairan 3,5 % wt NaCl pada daerah takikan. Selama waktu pembebanan, defleksi pada spesimen uji terus diamati dan pada akhir pengujian permukaan hasil patahan dilihat dengan menggunakan SEM, EDS dan Mapping. Kedalaman retak diukur dengan mikroskop optik. Pada pengujian SEM didapat bahwa mekanisme retakan yang terjadi adalah secara intergranular dan transgranular fracture. Pengujian hasil mapping menunjukan terdapat presipitasi magnesium hidrida (MgH2) pada patahan. Hasil pengujian mengetahui hubungan antara stress intensity factor, perambatan retak, kedalaman retak dan defleksi. Hubungan tersebut dapat diamati melalui grafik, yaitu semakin tinggi perambatan retak dan kedalaman retak, semakin tinggi pula stress intensity factor yang terjadi.

Hydrogen induced cracking is an event of material cracking due hydogen atoms entered the grain boundaries of a material in a large of amount. The hydrogen atoms would fill the grain boundaries of the material and eventually resulted in cracking. Events like this are usually called by hydrogen embrittlement. The purpose of this study was to characterize the hydrogen induced cracking in AA 5083 H116 material inside a 3,5% wt NaCl environment. This study is started with making the bending test tool with the scheme of Brown and Beachem and ASTM E 1681. The specimens used in this test was made in accordance with the specimen notched with electrical discharge machining (EDM) on its weld and heat affected zone (HAZ) from IZOD sample (ASTM E 23). To achieve the objectives in this study, the 4 specimens is testing by placing a 40 N constant loading for 5 weeks. To accelerate the process of hatching, during the loading, the specimens were soaked in a 3.5 % wt NaCl at the notched area. During load time, deflections in test specimens are continuously observed and the fracture surface of the specimens was examined with SEM, EDS, and Mapping. Crack depth were measured with an optical microscope. Observations on the SEM results shows the crack mechanism that occured is intergranular and transgranural fracture. The Mapping test results also showed that there are precipitated magnesium hybride (MgH2) on the fracture surface. There is also a relationship between the stress instensity factor, crack propagation rate, depth of the crack, and deflections. The relationship can be observed from the graph, it shows that the higher the crack propagation rate and crack depth, the higher stress intensity factor that occured.

Kata Kunci : Hydrogen induced cracking, stress intensity factor, AA 5083 H116, Penggetasan hidrogen.