Deni Ferdian

Study of the Effect of Cooling Rate on Eutectic Modification in A356 Aluminium Alloys

In this present work, an assessment of eutectic modification based on thermal analysis was performed on modified A356 alloy. The effect of various cooling rates which were achieved by means of casting samples with various moduli in sand and metallic moulds was investigated. Cooling curves recorded from thermocouples inserted in the centre of the samples showed characteristic undercooling and recalescence associated with (Al)-Si eutectic modification. The results showed that cooling rate has a role in observed modification level. Furthermore, differential thermal analysis was included to determine the eutectic melting temperature.

Microstructure analysis of synthesized iron substituted Ni44Fe6Mn32Al18 Heusler alloy

Chlorofluorocarbons (CFCs) which emitted to the atmosphere have been recognized to cause damage to the ozone layer. Alternative materials to replace the CFC’s role are those which have properties of the magneto caloric effect (MCE) like Heusler alloys. In this paper, we report results of synthesis studies of the magneto caloric materials based on Ni-Mn-Al which possesses the structure of Heusler alloy. Crystallographically, the alloy is a single phase system with a general formula of X2YZ which possesses the L21 (the Strukturberichte - SB) crystal structure. An iron substituted Ni44Fe6Mn32Al18 alloy was successfully casted by means of melting in a vacuum arc melting furnace. Series of microstructure as cast alloy which studied under SEM observation and EDAX analysis reveals that the cast sample consisted of at least 4 phases. These are the main phase of Ni-Mn-Al system with the additional minor phases of Al rich, Al-oxide and Al deficit main phases, respectively. Annealing process at 900 °C in oxygen free...

Method for detecting austenite grains in low-carbon steel after hot deformation

The structure of low-carbon steel after hot deformation at 1060 and 960°C with different degrees is studied. A procedure is developed for specimen etching in a reagent based on picric acid making it possible to detect clear austenite grain boundaries and sub-boundaries after hot deformation.

Synthesis of TiO2 Nanofluids by Wet Mechanochemical Process

Nanofluids have been developed in a search of new coolants with higher thermal conductivity compared to the conventional coolants, such as water or ethylene glycol. This research is conducted to observe the main characteristics, such as particle size, suspension stability, and thermal conductivity, of nanofluids produced from wet mechanochemical process with the addition of 0.02 vol% oleic acid. Milling process was conducted in conventional planetary ball mill for 15 hours. The results showed that nanoparticle was formed from micron size raw materials and dan dispersed simultaneously in water. Particle size distribution of particles which are less than 100 nm size were in the range of 51–100%. The ratio of thermal conductivity enhancement of the 1% vol TiO2 nanofluids compared with water without surfactant is 1.1. The ratio of thermal conductivity of TiO2 nanofluids increases in higher concentration of nanofluids. Oleic acid addition increases the particle stability of nanofluids and its ratio of thermal ...

Austenite to Ferrite Transformation after Hot Deformation of Low Carbon Steel

The aim of this work is to get the ferrite nucleation criteria from the recrystallized austenite grain after hot deformation in non isothermal condition. A series of rolling experiments have been performed with industrial C-Mn steel in two different temperatures of 1060 and 960 °C with sequence cooling cycle. The microstructure changes that taking place during hot rolling and after cooling has been examined by metallographic evaluation which allows the identification of ferrite transformation after austenite recrystallization. The recrystallization control was carried out using interrupted cooling method to obtain transformation from actual austenite grain. Using an approach of grain boundary interfacial area (Sv) calculation, which attempts to account the number of sites for potential nucleation of ferrite in thermomechanically processed austenite, an essential correlation of the correspond measured grains was developed. The influence of delay interval time after recrystallization to transformation is observed and the implication obtained is discussed. From those results, a hypothetical interaction between parameter and nucleation is described. It is concluded that, strain and holding time has a major role on the recrystallization process of austenite and bring an effect to ferrite grain refinement. The calculated Sv has indicated the potential sites of nucleation that are proliferated with increasing strain.

3D characterization by tomography of beta Al9Fe2Si2 phase precipitation in a Al6.5Si1Fe alloy

The microstructure evolution of beta phase during solidification of a synthetic Al6.5Si1Fe (wt.%) alloy has been investigated by in-situ synchrotron micro-tomography and post-mortem tomography. In-situ solidification was observed at a constant cooling rate of 10°C min-1, from above the alloys liquidus with the melt at 618°C down to 575°C which is just above the (Al)-Si-beta invariant eutectic reaction. Primary (Al) dendrites nucleated at 608°C, followed by the formation of beta-Al9Fe2Si2 phase starting at 593°C. After a rapid growth stage until 587°C as thin plates, beta phase continued to grow at a paced rate. Thickening of the plates was also evaluated and it was observed that the decrease in the lateral growth rate of the plates did not lead to an increase of their thickening rate. It was noted that the interconnectivity between beta precipitates increased as the solidification progressed. While nucleation of beta phase has previously been reported to occur on the alumina scale formed at the outer surface of the material, it is shown from post mortem tomography that bulk nucleation can occur as well.

Characterisation of rosette formation in an aluminium-silicon alloy

Differential thermal analysis has been used to investigate the effect of cooling rate on rosette formation during solidification of a synthetic Al–Fe–Si alloy. Rosettes can be characterised as a very fine multiphase structure within more or less convex areas dispersed in the matrix. Their formation during solidification is related with liquid entrapment and high solidification undercooling associated with the need of independent nucleation events of second phases. It is here shown that their density and internal coarseness depend on cooling rate. Further, metallographic observation of rosettes in contact with large precipitate of β-Al9Fe2Si2 phase allowed to conclude that this latter phase does not help silicon nucleation.

Effect of samarium in corrosion and microstructure of Al-5Zn-0.5Cu as low driving voltage sacrificial anode

Sacrificial Anode Low voltage is the latest generation of the sacrificial anode that can prevent the occurrence of Hydrogen Cracking (HIC) due to overprotection. The Al-5n-0.5Cu alloy showed the potential to be developed as the new sacrificial anode. However, the main problem is copper made Al2Cu intermetallic in grain boundary. Samarium is added to modify the shape of the intermetallic to make it finer and make the corrosion uniform. Several characterizations were conducted to analyze the effect of Samarium. Scanning electron microscope (SEM) and Energy dispersive spectroscopy was used to analyzed the microstructure of the alloy. Metallography preparation was prepared for SEM analysis. Corrosion behavior was characterized by cyclic polarization in 3.5% NaCl solution. The results show samarium can change the shape of intermetallic and refine the grains. In addition, samarium makes better pitting resistance and exhibits a tendency for uniform corrosion. It is indicated by the loop reduction (ΔEpit-prot). Current density increased as an effect of samarium addition from 6x10−5 Ampere (Al-5Zn-0.5Cu) to 2.5x10−4 Ampere (Al-5Zn-0.5Cu-0.5Sm). Steel potential protection increased after addition of samarium which is an indication the possibility of Al-Zn-Cu-Sm to be used as low voltage sacrificial anode.Sacrificial Anode Low voltage is the latest generation of the sacrificial anode that can prevent the occurrence of Hydrogen Cracking (HIC) due to overprotection. The Al-5n-0.5Cu alloy showed the potential to be developed as the new sacrificial anode. However, the main problem is copper made Al2Cu intermetallic in grain boundary. Samarium is added to modify the shape of the intermetallic to make it finer and make the corrosion uniform. Several characterizations were conducted to analyze the effect of Samarium. Scanning electron microscope (SEM) and Energy dispersive spectroscopy was used to analyzed the microstructure of the alloy. Metallography preparation was prepared for SEM analysis. Corrosion behavior was characterized by cyclic polarization in 3.5% NaCl solution. The results show samarium can change the shape of intermetallic and refine the grains. In addition, samarium makes better pitting resistance and exhibits a tendency for uniform corrosion. It is indicated by the loop reduction (ΔEpit-prot). C...

Coke and coal as reductants in manganese ore smelting: An experiment

Abstract The effect of coke and bituminous coal on the reduction of medium-grade manganese ore in ferromanganese production was investigated. Charges of 30 kg medium grade manganese ore, 12 kg limestone and varied amounts of coke and coal were smelted in a Submerged Electric Arc Furnace (SAF) at temperatures of 1300°C to 1500°C. The composition of the ferromanganese and the slag were determined by X-Ray Fluorescence. It was found that using coke as a single reductant resulted in a 96% yield of ferromanganese which was higher than by using coal either as a single reductant or in a mixture of coal and coke. It was also found that using coke as a single reductant resulted in the lowest specific energy consumption. Using coal as reductant produced ferromanganese containing high sulfur and phosphorus.

Effect of slag basicity in ferromanganese production using medium-grade manganese ore from East Java-Indonesia

ABSTRACT Ferromanganese is one of the most important alloying elements in steel industries. In this work, the production of ferromanganese was carried out using three-phase submerged mini electric arc furnace. The effect of slag basicity due to the addition of a various amount of limestone as fluxing agent on this smelting process was investigated. The chemical composition of ferromanganese and slag was analysed with X-ray fluorescence. From this experiment, the optimum slag basicity was 0.8 that produced 8.2 kg of ferromanganese with 78.1% Mn, 12.7% Fe, and 8.9% Si. It resulted from 30 kg of manganese ore, 7.5 kg of cokes, and 12 kg of limestone.