You Chul Kim

Factors dominating joint characteristics in Ti± Al friction welds

Abstract The dominant factors determining the joint characteristics (strength, ductility etc.) in friction welds between Ti and Al were investigated from both mechanical and metallurgical points of view. The principal factors determining the joint characteristics were not mechanical, as the residual stress and plastic strain generated by the friction welding were not especially high. Instead, it was found that the joint characteristics were dominated mainly by a metallurgical factor, that is, the thickness of the intermetallic compound layer produced at the interface. The critical thickness of the intermetallic compound layer was about 5 νm. When this type of joint is used in a high temperature environment, the working temperature and time should be carefully monitored. For long working times, the joint characteristics were greatly deteriorated as the thickness of the intermetallic compound layer increased.

Characterisation and generation mechanism of residual stress and plastic strain in Ti/AISI304L stainless steel friction welds

Summary This paper describes detailed FEM modelling performed to clarify the characteristics of residual stress and plastic strain generated during dissimilar metal friction welding operations. The results obtained may be summarised as follows: When bonding problems of dissimilar materials are being numerically analysed by an FEM thermal elastic‐plastic analysis, comparisons undertaken in the radial direction of both the distribution and magnitude of the z axis stress σz generated in both base metals adjacent to the bondline, as determined from the uniform cooling model from 800 °C to room temperature, provide a sound basis for a decision as to the suitability of the FEM mesh used. A comparison of the yield stress σY and temperature relationships in both base metals shows that the Ti base metal has the lower zero‐σY temperature (mechanical fusion temperature). Thermal diffusion in Ti/AISI304L stainless steel friction welds mainly occurs within a narrow region of around 20 mm from the bondline, and this st...

Mechanical properties and fatigue strength of high-manganese non-magnetic steel/carbon steel welded joints

Summary This paper describes performance tests of dissimilar material welded joints produced from carbon steel and a new type of high-manganese non-magnetic steel with improved machinability. The basic mechanical properties of these joints are first described. Fatigue tests are then conducted for purposes of fatigue strength design of the joints within the context of an evaluation of their suitability for application to welded structures, such as the steel bridges of magnetic levitation railways (linear motors). Dissimilar material welded joints with good penetration and integrity arc obtained. The results of the surface colour check and X-ray transmission tests of the welds suggest that they are free from any welding defects, such as hot cracking or blowholes. The tensile strength of the dissimilar material welded joints is, at 498 MPa, 10% higher than that of the carbon steel base metal (441 MPa). In the bending tests, the dissimilar material welded joints show good ductility without cracking under face...