Bondan Tiara Sofyan

Effects of microalloying with Cd and Ag on the precipitation process of Al–4Cu–0.3Mg (wt%) alloy at 200°C

Abstract The present work investigates the effects of individual and combined additions of Cd and Ag on precipitation processes in an Al–4Cu–0.3Mg (wt%) alloy. Analytical scanning transmission electron microscopy revealed that microalloying with Cd stimulates nucleation of θ′ phase on {001} α planes and that Cd-rich particles form on the rim and broad facets of the θ′ platelets. We interpret these observations to suggest that Cd nucleates heterogeneously at the θ′–α interface and that θ′ can also nucleate heterogeneously at the Cd–α interface. In the quinary alloy, it was observed that Ag and Cd additions seem to work independently resulting in a fine and uniform dispersion of both Ω and θ′. Furthermore, the hardening effect of the {111} α Ω phase appears to be more potent than other precipitates formed in this system since the hardness of the quinary alloy was intermediate between the Al–Cu–Mg–Ag and the Al–Cu–Cd alloys.

Development of Steel Wire Rope – Reinforced Aluminium Composite for Armour Material Using the Squeeze Casting Process

Steel wire rope – reinforced aluminium composite - has been developed to improve the ballistic properties and mobility of armour material. Critical to obtaining ballistic resistance is that the materials must be sufficiently hard and strong, especially at the surface where a projectile will first make impact. To obtain this resistance, aluminium alloys can be strengthened by adding Cu and Mg. This research studied the ballistic properties of aluminium composites with varied Cu and Mg content. The matrix used in this study was an Al-7Si master alloy with 0.08-1.03 wt. % Mg and 0.05-3.75 wt. % Cu, both independently and in combination. A high carbon steel wire rope was used as strengthening material. The samples were produced through the squeeze casting process with a pressure of 1 MPa at semi-solid melting temperatures of 590-610 °C. The slab was then rolled for 10 % reduction to increase the hardness. Ballistic testing was performed in accordance with ASTM F1233 by using a 9 mm calibre projectile and 900 direction. Micro structural observation was conducted in the as-cast and ballistic samples, performed with optical microscope and scanning electron microscope (SEM). The results showed that squeeze casting may improve interfacial wettability and reduce void. The increase in Mg resulted in the decline of interfacial voids, but Cu addition tended to increase them. The aluminium armour was able to withstand a 9 mm calibre projectile, although some cracks were visible. The wire rope was not effective in stopping the penetration of a 7.62 mm calibre projectile.

Effects of Deformation and Annealing Temperature on the Microstructures and Hardness of Cu-29Zn-0.6Bi Brass

The use of lead-free brass is growing due to the restriction of the lead content in many components. Bismuth replaces lead in the brass alloys and contributes to the machinability and pressure tightness characteristics. However, Bi is immiscible in copper and fills the inter-dendritic spaces during solidication that yields negative impacts on the mechanical properties. This research studied the effects of addition of 0.6 wt. % Bi on the characteristics of Cu-29Zn alloy during cold rolling and subsequent annealing process. The Cu-29Zn-0.6wt.%Bi alloy was produced by gravity casting in a metal mold with the dimension of 110x110x6 mm3. The as-cast plate was homogenized at 800 °C for 2 hours and then cold rolled with the level of deformation of 20, 40 and 70 % in multiple passes. The samples with 70% deformation was annealed at 350, 400 and 450 °C for 15 minutes. Characterization of materials included Vickers hardness measurement and microstructural observation by using optical microscope and SEM. The results showed that addition of Bi reduced the grain size, formed discrete globules in the interdendritic areas and increased the hardness. The globules as dispersoid bismuth deformed and filled intergranular spaces during rolling and promoted the formation of cross slip mechanism at the 20% deformation. At the 40% deformation, the globules led to more closely spaced twin lamellae and increased the twinning density. The phenomena created an inhomogeneous deformation and promoted the formation of shear band. Annealing process dispersed the Bi globules into tight structures along the grain boundaries.The presence of dispersed bismuth increased the rate of recrystallization during annealing due to the increased in potential site for nucleation. In contrast, the dispersed bismuth acted as the pinning agent that inhibited the grain growth and developed smaller grain size which resulted in higher hardness.

Characterization of Al-7Si-Mg-Cu Turbine Impeller Produced by Investment Casting

Application of a light-weight material, such as an aluminum alloy, on a turbine impeller can enhance the efficiency of an Organic Rankine Cycle power plant that operates at temperatures below 150 °C. The density of an aluminum alloy only one-third that of steel. However, increased strength of aluminum alloys is needed for turbine impeller qualification. Investment casting was chosen to produce radial inflow turbine impeller due to their complex geometry and precision. It can replace machining process, which is time-consuming and less efficient because of material removal. This study describes the investment casting process used to produce a radial inflow impeller turbine. The study also identifies defects, microstructures and properties of radial inflow turbine impeller. The turbine impeller were produced from Al-7Si-4Mg alloy with 0.38, 3.82, and 6.0 wt. % Cu. Visual examination showed that the turbine impeller was free of macro defects and misruns. Microstructures were characterized by Optical Microscopy and SEM. The structures consisted of α-Al, Si eutectic, AlMgSi, AlMgFeSi (Chinese script) and CuAl2. The higher hardness value of 54HRB was affected by Cu content due to the good mechanical properties of fasa CuAl2.

Effects of Manganese on the Microstructures, Mechanical Properties and Deformation Characteristics of Cu-29Zn Alloy

Deformation characteristics of brass alloy are still under discussion, particularly concerning the critical level of when the change of deformation mechanism occurs. Previous research showed that the addition of Mn on brass alloys resulted in grain refinement and mechanical properties alteration. However, the effects of Mn on the deformation characteristic of brass alloys have not been investigated. In this research, Cu-Zn-xMn alloys were manufactured by gravity casting process using pure Cu and Zn ingots, as well as Mn chips as the feeding materials. Mn addition was varied to 1.26, 3.48, and 5.83wt.%. As-cast samples were homogenized at 800 °C for 2 h in a muffle furnace. The samples were then cold-rolled with the level of deformation of 20, 40, and 70 %. Samples characterization includes chemical composition analysis, microstructure observation, tensile and hardness testing. The results showed that addition of Mn for 5.83 wt.% and above created β’ phase, which is richer in Mn compare to that in the matrix. This phase segregated in the grain and along the grain boundary with irregular forms. Significant increase in hardness, yield and tensile strengths was observed with addition of Mn. The maximum elongation was achieved by addition of 3.48 wt.% Mn, while further addition tended to decrease it. At 20% deformation, slip dominated and its density reduced with addition of Mn. When the deformation level increased to 40%, twinning replaced slip as the predominant mechanism. Twinning density is slightly increase with the presence of Mn. Further deformation at 70% produced shear bands and flattened the β’ phase. Greater Mn content led to formation of more shear band.

Influence of Compaction Pressure on Density, Bending Strength, and Microstructures of Al2O3-SiC-ZrO2 Ceramic Matrix Composites with Nb2O5 Additives

Ceramic matrix composites (CMCs) are known to have high hardness, temperature and corrosion resistance, while being comparatively lightweight. One of many external factors that influence the mechanical properties of CMC is the compaction pressure given during fabrication process. Generally, greater amount of applied compaction pressure will result in improved final product density and bending strength. In this research, a type of CMCs was fabricated using Al2O3, SiC, and ZrO2 powder mixed with Nb2O5 additive of 81Al2O3-10SiC-5ZrO2-4Nb2O5 wt. % composition. Fabrication was done through mixing, compacting, and sintering process. Compaction was performed at 257, 308, and 359 MPa and finished with sintering process at 1400 °C for 4 h. Final samples were characterized by density measurement, 3-point bending strength testing, XRD for phase investigation, and microstructure observation using SEM-EDS. Results showing that samples with 308 MPa compaction pressure possessed the highest density and bending strength of 3.29 gr/cm3 and 14.91 MPa, respectively. These numbers however, declined on samples with higher compaction pressure of 359 MPa due to the formation of porosities caused by entrapped gas that failed to exit the sample of which compaction pressure was considered to be overwhelmingly high.

Effects of Magnesium Content on Ballistic Performance of Al-8Zn-SiC Composite after Heat Treatment Process

SiC – reinforced aluminium composite - has been developed to improve the ballistic performance and mobility of the armour material. Critical to obtaining ballistic resistance is that the materials must be sufficiently hard and strong, especially at the surface where a projectile will first make impact. To achieve this resistance, aluminium alloys can be strengthened by adding Zn and Mg, and reinforced with silicon carbide. This research studied the ballistic properties of aluminium composites with varied Mg. The matrix used in this study was an Al-8Zn alloy with 3-5 wt. % Mg. Silicon carbide particulate of 15 % volume fraction was used as strengthening material, which was added to the liquid matrix by stirring at 5000 rpm. The liquid composite was then squeeze cast at a pressure of 72 MPa. Then the composites were heat-treated and coated to improve the ballistic performance. Ballistic testing was performed in accordance with ASTM F1233 by using 7.62 calibre projectiles. Microstructural observation was conducted in samples, performed with optical microscope. The results showed that the as-cast hardness of the composite increased with addition of Mg content of 3, 4 and 5 wt. %. The peak hardness after ageing at 200 °C also increased with Mg addition. However, the composites were not able to withstand the 7.62 mm calibre projectile.

Effect of Treatment Process on Hardness of Al7Si-Mg-Zn Matrix Composite Reinforced with Silicon Carbide Particulate

Aluminium matrix composite with silicon carbide reinforcement has been developed to increase the hardness of the composite. The determining factors in the development of this material are alloy element content, rolling process and heat treatment. In this research, Al-7Si alloy with Zn and Mg element content variation was made as the matrix to strengthen the aluminium. The reinforcement is silicon carbide (SiC) in the form of particle with volume fraction of 520%. Rolling process and heat treatment were conducted to further increase the hardness. Material characterisation is conducted with chemical composition testing, microstructure observation, and hardness testing. Research showed that after rolling process with 10% reduction, the hardness of composite is increased. The improvement of hardness on precipitation heat treated composite after rolling process tend to decline compare to non-rolled composite.

Effects of Combination of 0.02 wt % Sr and Ti on the Characteristics of AC4B Alloys Produced by Low Pressure Die Casting

Aluminium AC4B alloy is widely used in automotive industries for various components. However, when this alloy is used to produce motorcycle cylinder head by Low Pressure Die Casting (LPDC) process, high reject rate was often found due to shrinkage, porosity and misrun. Addition of grain refiner and modifier is an alternative for this problem, through the control of solidification process that results in grain refining and microstructure modification. This study was aimed to investigate the effect of combination of 0.02 wt. % Sr modifier with variation of Ti grain refiner on the characteristics of AC4B alloy and the reject rate of cylinder head components. The Ti grain refiner was varied 0.063, 0.083 and 0.108 wt. % Ti and added at the holding furnace prior to LPDC process. A series of test was conducted including hardness test from the thin and thick regions of the part, tensile test, fluidity test, vacuum test as well as observation of microstructure by using optical microscope and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray Analysis (EDAX). The results showed that the higher the Ti content, the higher the hardness for both thin and thick areas, the lower the fluidity of the molten metal. At the maximum level of Ti of 0.108 wt. % and 0.02 wt. % Sr, the reject rate was significantly reduced from 3.59 % to 1.38 %.

Development of Phase Field Simulation for the Growth of Dendrite Structure of Al-Si Cast Alloy

Micro to nano scale study of dendrite structure is important in order to have better properties control of casting product. The present study concerns on the morphological study of dendrite structure by phase-field simulation, in order to obtain the morphological growth of this structure that close its real morphology. Focus was given on the morphological growth of dendrite structure of Al-Si cast alloys, therefore thermodynamic data were taken for this type of materials. Anisotropy noise, strength of anisotropy and different undercooled conditions were applied as the variable parameters in the present works. It was observed that by introducing higher anisotropy noise, higher degree fragmentation of dendrite structure was obtained. Similar condition was obtained by introducing higher strength of anisotropy value, that higher degree of fragmentation was obtained. Both of these phenomena was also supported by the heat flux rate features of these variations that higher heat flux rate to almost all direction was obtained with the higher value of anisotropy noise and strength of anisotropy. In addition it was also observed that higher degree fragmentation of dendrite only possible to occur if sufficient undercooled condition established.