• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.209-216
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• 1995

In order to investigate the effect o green microstructure on the sintering behavior and properties of AlN ceramics, samples were prepared by slip casting and dry pressing. The slip cast samples had high green density, fine pore size and narrow pore size distribution. They showed much higher sinterability and more homogeneous sintered microstructure compared to the dry pressed samples. Both increased thermal conductivity and flexural strength for samples prepared by slip casting could be attributed to the improved microstructural homogeneity with isolated second phase(s).

• Transactions of Materials Processing
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• v.23 no.6
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• pp.386-391
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• 2014

In the current study, Al-Mn-Zn alloys are strip-cast and used as the base alloy for the core of aluminum clad sheets used in automotive condenser fins. Transition elements such as Cu and Cr are added to the base core alloy in order to improve the properties of the clad sheets. The AA4343/Al-Mn-Zn-X(X: Cu, Cr)/AA4343 clad sheets are fabricated by roll bonding and further cold-rolled to a thickness of 0.08 mm. Clad sheets were intermediately annealed during cold rolling at $450^{\circ}C$ in order to obtain 40% reduction at the final thickness. Tensile strength and sag resistance of the clad sheets are improved by Cu additions to the core alloy, while corrosion resistance is also increased. Cr-additions to the clad sheets enhance sag resistance and provide low enough corrosion, although tensile strength is not improved. The effect of Cu and Cr additions on the properties of the clad sheets is elucidated by microstructural analysis.

• Journal of Korea Foundry Society
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• v.34 no.3
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• pp.87-93
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• 2014

Thixo-extrusion of semi-solid 7075 aluminum alloy and the mechanical properties of its extrudates were investigated. The semisolid alloy was prepared by a cooling slope cast. In other to perform thixo-extrusion, semi-solid 7075 aluminum alloy billets were reheated at the reheating conditions reported in a previous study. The maximum extrusion pressure in thixo-extrusion was 615MPa. This was lower than that of conventional hot extrusion ($P_{max}=940MPa$) at the same extrusion conditions due to the increased fluidity of the alloy billet in the semi-solid state. The values of Rockwell hardness (scale B) at the extrusion direction of the as thixoextruded bar were 48~53HRB and the difference in Rockwell hardness between the transverse direction and the extrusion direction was 5HRB or less. The results show that thxio-extrusion of semi-solid 7075 Al alloy improves the workability and anisotropic with the extrusion direction compared with hot extrusion of the conventional alloy.

• Journal of Korea Foundry Society
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• v.39 no.4
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• pp.61-74
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• 2019

The effects of Sr and (Ti-B) additives on the impact and fatigue properties of recycled (35% scrap content) AC4A aluminum alloy are investigated here. The acicular morphology of the eutectic Si phase of as-cast specimens was converted to the fibrous one with Sr additives. The grain size of the α-solid solution decreased by the addition of (Ti-B) additives. The crack initiation energy (E_i) of the impact absorption energy decreased due to the incorporation of an oxide film and inclusions depending on the scrap used. The modification of the eutectic Si morphology by Sr additives is considered as the main factor of the increase of the average impact absorption energy (E_t). The addition of (Ti-B) additives contributed to an increase in the occurrence of crack deflections due to the refining of α-Al grains, resulting in improved fatigue properties.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.3
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• pp.172-176
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• 2005

Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is A6061, A7075 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of A6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.

• Journal of the Korean institute of surface engineering
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• v.42 no.1
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• pp.13-20
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• 2009

Friction stir welding(FSW) was developed as a new solid state welding technique by The Welding Institute (TWI). On the basis of FSW, a new processing technique, friction stir processing (FSP), has recently been developed. FSP has been applied to cast aluminum alloy to modify the microstructure to enhance mechanical characteristic. FSP is a new solid state processing technique for microstructural modification in metallic materials. FSP has been applied to aluminum alloy to modify the microstructure to enhance mechanical characteristic. In this study, we investigated optimum condition friction stir processing with the evaluation of mechanical characteristic for 5456-H116 Al alloy. The mechanical characteristics of base metal similar with in 15 mm/min, 250 RPM with full screw probe. This condition is concluded that optimum friction stir processing condition. The result of this investigation will be able to application for repair of welding part for aluminum ship.

• Journal of Korea Foundry Society
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• v.24 no.2
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• pp.94-100
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• 2004

Gas porosity which is a common defect in aluminum alloy casting, is also thought to be severer in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process variables such as the melt treatment, the cooling rate and pouring temperature on the density and mechanical properties in A356.2 castings with simple bar shape. The density of grain refined specimen was slightly lower than that of degassed one, but was higher than that of no treated one and that of shot ball packed specimen was higher than the other specimens. The tensile strength and elongation were in the ranges of $200{\sim}230MPa$ and $0.5{\sim}1.5%$ respectively. The density and hardness of lost foam cast specimens decreased with increase in pouring temperature.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.165-173
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• 2003

As the cycling time of new products have become more and more short in recent years, the demand for lowering the cost and reducing the production time becomes stronger. In order for the demand, the rapid prototyping and rapid tooling technology have been used. It has been widely known that RP technology has advantages with fabricating 3-D object having a complicated geometric shape. RP products, however, have a limitation with applying to the real die and mold because soft materials such as resin, paper and wax has been mostly used in RP technology. So in this paper, the RP products have been copied to semi-metallic soft tools using the mixture of metal fillers and epoxy resin. In order to evaluate the effect of the fillers on the characteristics of semi-metallic soft tools, three fillers are used including commercial aluminum powder, cast iron powder recycled by machining chips, and aluminum short fiber made by self-excited vibration technique. Besides, in the case of aluminum powder, the change of characteristics of semi-metallic soft tools is also tested according to the volume fraction of the powder.

• Proceedings of the KWS Conference
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• 1996.10a
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• pp.3-15
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• 1996

The formation of a thicker hard alloyed layer have been investigated on the surface of aluminum cast alloy (AC2B) by PTA overlaying process with Cr, Cu and Ni motel powders under the condition of overlaying current 125-200A. overlaying speed 150 mm/min and different powder feeding rate 5-20 g/min. In addition the characteristics of hardening and wear resistance of alloyed layer here been examined in relation to the microstructure of alloyed layer. Main results obtained were summarized as follows: 1) There was an optimum overlaying condition to get a good alloyed layer with smooth surface. This good layer became easy to be formed as increasing overlaying current and decreasing powder feeding rate under a constant overlaying speed. 2) Cu powder was the most superior one in metal powders used due to a wide optimum overlaying condition range, uniform hardness distribution of Hv250-350, good oar resistance and freedom from cracking in alloyed layer with fine hyper-eutectic structure. 3) On the contrary, irregular hardness distribution was usually obtained in Cr ar Ni alloyed layers of which hardness was increased as Cr or Ni contents and reached to maximum hardness of about Hv400-850 at about 60wt%cr or 40wt%Ni in alloyed layer. 4) Cracking occurred in Cr or Ni alloyed layers with higher hardness than Hv250-300 at mere than 20-25wt% of Cr or Ni contents in alloyed layer. Porosity was observed in all alloyed layers but decreased by usage of spherical powder with smooth surface.

• Korean Journal of Materials Research
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• v.31 no.12
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• pp.672-676
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• 2021

In this paper, the effect of Ni (0, 0.5 and 1.0 wt%) additions on the microstructure, mechanical properties and electrical conductivity of cast and extruded Al-MM-Sb alloy is studied using field emission scanning electron microscopy, and a universal tensile testing machine. Molten aluminum alloy is maintained at 750 ℃ and then poured into a mold at 200 ℃. Aluminum alloys are hot-extruded into a rod that is 12 mm in diameter with a reduction ratio of 39:1 at 550 ℃. The addition of Ni results in the formation of Al₁₁RE₃, AlSb and Al3Ni intermetallic compounds; the area fraction of these intermetallic compounds increases with increasing Ni contents. As the amount of Ni increases, the average grain sizes of the extruded Al alloy decrease to 1359, 536, and 153 ㎛, and the high-angle grain boundary fractions increase to 8, 20, and 34 %. As the Ni content increases from 0 to 1.0 wt%, the electrical conductivity is not significantly different, with values from 57.4 to 57.1 % IACS.