Jongsup Lee

Effect of bonding interface on delamination behavior of drawn Cu/Al bar clad material

Cu/Al bar clad material was fabricated by a drawing process and a subsequent heat treatment. During these processes, intermetallic compounds have been formed at the interface of Cu/Al and have affected its bonding property. Microstructures of Cu/Al interfaces were observed by OM, SEM and EDX Analyser in order to investigate the bonding properties of the material. According to the microstructure a series of diffusion layers were observed at the interface and the thicknesses of diffusion layers have increased with aging time as a result of the diffusion bonding. The interfaces were composed of 3-ply diffusion layers and their compositions were changed with aging time at 400 °C. These compositional compounds were revealed to be η2, (θ+η2), (α+θ) intermetallic phases. It is evident from V-notch impact tests that the growth of the brittle diffusion layers with the increasing aging time directly influenced delamination distance between the Cu sleeve and the Al core. It is suggested that the proper holding time at 400 °C for aging as post heat treatment of a drawn Cu/Al bar clad material would be within 1 h.

Evaluation of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials

The aim of the present study is to identify the properties of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials by transmission electron microscopy and nano-indentation analyses. Cu/Al clad materials were fabricated by hot pressing under 200 MPa at 250 °C for 1 h and then heat treated at 400 °C for 1 h. Nano-indentation measurement was conducted to evaluate the nanohardness and modulus of the intermediate phases formed between the Cu/Al interfaces. A 3-tier diffusion layer was observed at the Cu/Al interfaces. Knoop microhardness values at the bonding interface were 7 to 11 times that of the Cu and Al matrix metals. The intermediate phases formed at the bonding interface were Al4Cu9, AlCu, and Al2Cu. A mapping analysis confirmed that the Al and Cu particles moved via mutual diffusion toward the intermediate phases formed at the bonding interface. The nanohardness values of η2-AlCu and γ1-Al4Cu9 were 4 to 7 times that of the Cu and Al matrix metals. Nanohardness and Knoop microhardness measurement curves exhibited similar tendencies. The rigidity values of the respective intermediate phases can be arranged in descending order as follows: γ1-Al4Cu9 > η2-AlCu > θ-Al2Cu.

Effect of hydro co-extrusion on microstructure of duo-cast Al 3003/Al 4004 clad materials

The effects of hydro co-extrusion on the microstructure changes of aluminum hybrid duo-cast Al 3003/Al 4004 clad materials were studied. The specimen of duo-cast Al 3003/Al 4004 clad materials was in circle shape, and was composed of Al 3003(outside) and Al 4004(inside) materials. The specimen was extruded by the hydro co-extrusion equipment. The manufacturing conditions of the specimen were 423 K in temperature and 5 in extrusion ratio. The dimensions of the specimen were 80 mm in diameter of the Al 4004 material and 35 mm in thickness of the Al 3003 material before the hydro co-extrusion process, and 30 mm in diameter and about 5 mm in thickness after the extrusion process, respectively. The microstructure and the hardness for two specimens were investigated. The hardness value of cross section in the duo-cast Al 3003/Al 4004 clad materials before the extrusion process was increased in form of the parabola toward the center. However, after the extrusion process, it was almost constant in the portion of Al 4004 material. Lots of big voids above 1 mm in diameter in the specimen existed in the interfacing region of Al 3003 and Al 4004 materials before the extrusion process. These big voids disappeared after the process of hydro co-extrusion.

Numerical studies on the swaging process of tubes with variable wall thickness for monobloc driving shafts

Abstract This study analyzed thickening trends of the variable cross-section tube in relation to swaging process variables to present an effective design for the tube manufacturing process. The extent of thickening was evaluated through a finite element analysis of the swaging process with varying process variables such as die shape and initial tube thickness. As a result, the amount of thickening was found to improve with decreasing diameter reduction, taper angle, and initial tube thickness.

Deformation characteristics at the Cu-Al contact surface during hydrostatic extrusion of a biaxial Cu-Al bar

This work is concerned with the deformation behaviours at the Cu-Al contact surface during hydrostatic extrusion of a concentric Cu and Al bar. In general, the unavoidable oxidisation at the Cu-Al contact surface prevents the bonding at the Cu-Al contact. A ‘local extrusion’, defined as a material flow through a fractured and expanded oxidised layer, is necessary for the successful bonding at the Cu-Al contact in a post process. Experiments consisting of extrusion and sintering with a biaxial Cu-Al bar are performed and it is confirmed that a ‘local extrusion’ does occur. In finite element studies, focuses are given to the behaviours of the first principal strain and the stress component normal to the Cu-Al contact profile since they are essential parameters for the success of a ‘local extrusion’. In this work, half die angle and extrusion ratio are considered as the most important process parameters. Effects of such process parameters on the deformation characteristics at the Cu-Al contact surfaces during hydrostatic extrusion are carefully examined.