Sung Chul Lim

Fabrication of Copper Clad Aluminum Wire (CCAW) by Indirect Extrusion and Drawing

The optimized extrusion conditions from the present research were the extrusion temperature of 573~623K and the extrusion ratio(A0/A) of 21.39. Above the extrusion temperature of 623K, the fracture of sheath material was observed. It is due to the difference of flow stress between the sheath material and the core material during extrusion process. The bonding strength increased with increasing the extrusion temperature and the extrusion ratio. The bonding strength increased with increasing the annealing temperature. However, over 573K, it decreased abruptly since the thick and brittle intermetallic compounds of larger than 3µm were formed. The electricalconductivity of copper clad aluminum wire was about 70%IACS without annealing.

Effects of Core Material on Extrudability of Cu/Pure Al, Cu/Al3003 Clad Composites by Indirect Extrusion

We investigated about the effects of core material(Pure Al, Al3003) on extrudability such as the maximum extrusion ratio and the bonding strength of Copper Clad Aluminum(CCA) by indirect extrusion. As a results of this experiment, the maximum extrusion ratio of Cu/Al3003 was 38, which was larger than 21.39 of Cu/Al(Cu/pure Al). It was because that the difference of flow stress between copper as the sheath material and Al3003 as the core material was smaller than that of between copper and pure aluminum under the same extrusion temperature of 623K. The bonding strength gradually increased when the extrusion ratio increased, on the other hand, the bonding strength of Cu/Al3003 was higher than that of Cu/Al under same extrusion conditions. The diffusion layer thickness that affected bonding strength was not affected by the kind of core material, but it gradually increased when the extrusion ratio increased. It was thought that Cu/Al3003 had a more intimate diffusion layer than Cu/Al had because the extrusion pressure of Cu/Al3003 was higher than that of Cu/Al under the same extrusion conditions.

The Effect of Electromagnetic Stirring on the Semi-Solid Microstructure of High-Melting Alloys

Most of the work reported at this conference concerned the semi-solid processing of low melting point alloys, and in particular light alloys of aluminum and magnesium. It also can be true for the higher melting point alloys, such as Cu alloys. The purpose of this paper is to develop a semi-solid microstructure of Cu alloys using electromagnetic stirring applicable for squirrel cage rotor of induction motor. The size of primary solid particle and the degree of sphericity as a function of the variation in cooling rate, stirring speed, and holding time were observed. By applying electromagnetic stirring, primary solid particles became finer and rounder relative to as-cast sample. As the input Hz increased from 30Hz to 40Hz, particle size decreased. The size of primary solid particle was found to be decreased with increasing cooling rate. Also, it decreased with stirring up to 3 minutes but increased above that point. The degree of sphericity became closer to be 1 with hold time. Semi-solid microstructure of Cu alloys, one of the high melting point alloys, could be controlled by electromagnetic stirring.

Fabrication and Properties of TiB2 Reinforced Cu Composites by Electromagnetic Stirring

Cu-Ti and Cu-B alloys were separately cast in vacuum arc melting furnace for alloying. These alloys were added to the copper melt of 1500K in the induction furnace and performed electromagnetic stirring at 1000rpm. The cast ingot(dia : 70mm, length : 100mm) was hot extruded with the extrusion ratio of 13:1 after heating at 1073K for 1 hour. The TiB 2 precipitates were observed in the extruded materials and the mean size of TiB 2 precipitates was found to be about 1.5µm. The volume fraction of TiB 2 varies due to the density difference between the TiB2 and the copper melt. With the increasing of TiB2 contents from 3 to 8 vol.%, the hardness and the tensile strength increased from 951 to 140Hv and from 248 to 278MPa, respectively, and the electrical conductivity decreased from 82 to 70%IACS. However, the mean size of TiB 2 particle was not increased despite increasing an annealing temperature.

The Effects of Heat Treatment on the Bonding Strength of Surface-Activated Bonding (SAB)-Treated Copper-Nickel Fine Clad Metals

Surface activated bonding (SAB) is a novel method for the precise joining of dissimilar materials. It is based on the concept that two atomically clean solid surfaces can develop a strong adhesive force between them when they are brought into contact at high vacuum condition without high deformation at a 40~90%. With this SAB process, the effects of heat treatment on the bonding strength of surface-activated bonding (SAB)-treated copper-nickel fine clad metals were investigated. An increase in the SAB rolling load of the copper-nickel fine clad metals increased the peel strength after heat treatment, indicating that increases in the SAB rolling load decreased the interface voids formed by initial micro-range surface roughness between the clad materials in the SAB cladding process. Unlike conventional cold rolling, outstanding interface diffusion between the clad materials was not observed after heat treatment. In addition, the peel strength increase of the clad metals compare with initial peel strength increased with SAB rolling load (<1% reduction ratio at a roll load of 5000 kgf ) up to 3.99 N/mm after heat treatment.

A Control of Microstructure of A356 Alloy by Sequential Semi-Solid Process

The study on rheocasting has been conducted based on examination for destruction, growth, ripening of solid state in accordance with various changes in cooling. And flow characteristics of slurry for high liquid range rather than practical use has gotten attention. However, the characteristics of existing rheocasting and thixocasting are better mechanical property than competing process die casting but it’s competitiveness as automotive or electric electronic parts which cost of product is important. And productivity also has been decreased. Because die-casting techniques has been advanced such as vacuum, mold auto temperature control etc. Most of the work reported at this conference concerned the semi-solid processing of low melting point alloys, and in particular light alloys of aluminum and magnesium. Therefore, the aim of this study is to devise the original strength of semi-solid process by sequential semi-solid process. The size of primary solid particle and the degree of sphericity as a function of the variation in cooling rate, stirring speed, and holding time were observed. By applying electromagnetic stirring, primary solid particles became finer and rounder relative to as-cast sample. With this background, this research conducted electromagnetic stirring through slurry deliverance of sequential process through A356 alloy electromagnetic stirring pump (30Hz, 130A) with Sequential Semi-Solid Process device to assess the microstructures, primary particle size, degree of sphericity change in A356 alloy in accordance of solid-fraction, stirring speed, and stirring maintenance time.

Fabrication of Rod type Cu54Ni6Zr22Ti18 Bulk Amorphous Alloy by Warm Extrusion Process

In this study, rod type Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm extrusion of amorphous powders was investigated. To get bulk type amorphous alloy, the Cu54Ni6Zr22Ti18 amorphous powders which has a particle size below 63( and wide supercooled liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were filled in a Cu can with an inner dimension 20×2×50mm in air, evacuated, sealed and then precompacted in the press. Before extrusion, the billet was heated with heating rate of 50K/min and the holding time was about 5min. The extrusion temperature was 723K and the extrusion ratio was increased from 2 to 5. By warm extrusion of amorphous powders, a fully amorphous Cu54Ni6Zr22Ti18 bulk type alloys were successfully synthesized. The conditions for extrusion were decided based on the time-temperature-transformation curve and DSC analysis. Phase analysis was performed by XRD. The result of the phase analysis indicated that Cu54Ni6Zr22Ti18 bulk rod type samples having fully amorphous phase could be obtained until extrusion ratio of 4 at extrusion temperature of 723K, but partial crystalline phase would be observed in the bulk rod type alloy fabricated at extrusion ratio of 5.

Extrudability and Bonding Strength of Copper Clad Aluminum Alloy Composites Produced by Indirect Extrusion Process

This paper described extrudability and bonding strength of copper (TPC) clad aluminum alloy (pure Al, Al3003, Al5005, and Al7072) composites produced by indirect extrusion at 350°C with extrusion ratio of 21.39. Conical typed die with semi angle of 30°. Carbon oil was used to reduce the friction between billet/sleeve and billet/die. Maximum extrusion pressure was estimated to 491MPa for the Cu/Al, 714MPa for the Cu/Al3003, 820MPa for the Cu/Al5005, and 743MPa for the Cu/Al7072 alloy composites. No surface fracture was observed. From SEM observation, diffusion layer between the sheath material and the core material of extruded composites is observed and its thickness was measured to about 1.5㎛. The bonding strength was estimated to 65MPa for the Cu/Al, 89.3MPa for the Cu/Al3003, 70MPa for the Cu/Al5005, and 75MPa for the Cu/Al7072 alloy composites.

Thermophysical Behavior of Micro Void in μ-Via of Microelectronic Substrate during Reliability Test

The μ-via in microelectronic substrate should have multiple purposes, one of them is to allow to the path of signal or current from electronic devices. The micro void can be easily formed in μ-via because μ-vias are filled with a screen printing process and the size of via is small. The residual void has been known as crack initiation of copper layer during a reliability test. The solder resist filling process and the behavior of a residual void in μ-vias were investigated. The void extraction process was very effective comparing with the conventional process to remove a residual void. As extracted with 1.5 atm for more than 30 sec, the residual void in μ-BVH was perfectly eliminated.

Surface Roughness of Cu-Be Alloy (C17200) Rod Alloy Produced by Horizontal Type Continuous Casting Process

Cu-Be alloy (C17200) rod having diameter of 23.5mm was produced by a vacuum continuous casting method at furnace temperature range of from 1240°C to 1260°C with casting speed range of from 35mm/min to 103mm/min. When the furnace temperature was 1240°C and 1250°C, Cu-Be alloy rod without fracture could successfully produced at high casting speed of 103mm/min. However, when the furnace temperature was 1260°C, the breakout occurred at casting speed faster than 78mm/min. Surface roughness (Ra) increased with increasing not only a furnace temperature but also a casting speed.