Manufacturing technologies
Automobile structure, Gas turbine, Mold

Microstructural control of a joint by linear friction welding
and its application
Joining and Welding Research Institute
Professor Hidetoshi Fujii
https://researchmap.jp/read0051741?lang=en

Abstract
We established “Perfect welding technology” which enables
continuous welding of metal materials as if without joint part. Regarding solid phase welding of heating up on pressing of material
to be welded, we succeed in controlling of welding temperature bywelding pressure, due to the invention of unexpected welding principle i.e. “Application of high welding pressure causes descendof welding temperature”. In existing welding method, the joint part
became the singular element of structure. Therefore, the propertyof metal material structure could not be made full use of the metalmaterial. However, in “Pressure Control Linear Friction Welding”
joint parts can be regarded same as the base material. For example, as for titanium alloy and steel, reliability of the joint part can besecured by non-transformation welding, and as for aluminum alloy,
softening of heat affected zone can be suppressed completely.

Manufacturing technologies▍ Background & Results
Welding technology is indispensable for manufacturing metal
structure, therefore various kinds of welding methods have beendeveloped. However, in case of titanium alloy and steel, it is very
difficult to obtain the welded body which shows the property ofbase material in full scale, due to the embrittlement of the joint partcaused by phase transformation. In case of aluminum alloy, it isvery difficult to control softening of the joint part caused by temperature increase in welding. Even in solid phase welding such asFriction Stir Welding (FSW) without melting material, it is necessary
to decide structure design considering strength of the joint part.
To solve these problems, we studied how to decrease welding
temperature by focusing on Linear Friction Welding (LFW). It is revealed that welding temperature increases by applying lower pressure and high pressure led to low welding temperature. This is dueto the principle that welded interface is deformed at lower temperature by applying higher pressure. By utilizing this principle, welding
temperature can be controlled accurately. For example, aluminumalloy was welded at 200℃, and the joint part showed completely
same hardness as base material. Thus, the joint part is no longer
the singular element, we can consider the joint part same as thebase material. As a result, ideal welding structures utilizing andkeeping the original property of base materials can be realized.

adds requisite minimum material”. Additive manufacturing which
can build up metal material in any desired shape and size will berealized.

Fig. Hardness distribution of Al6061-T6 joints
Formation of softening region can be completely suppressed by new LFW method.

Fig. Schematic drawing of LFW
In linear friction welding, a softened flash is discharged from a welding interface
to form a new surface to accomplish the welding.

▍ Significance of the research and Future perspective
By utilizing this research result, considering of decrease instrength and reliability in joint parts become unnecessary. Superior welding structure that shows original property of titanium alloy,
steel and aluminum alloy which is strengthened by various method
can be obtained. Moreover, this welding method can be appliednot only for manufacturing of metal structure but also utilized as
partial reinforcement and repair technology. It would contributethe conversion from “conventional manufacturing method which
deletes material by cutting” to “new manufacturing method which

Fig. Cross sectional image of A6061/A6061 weld interface
Very thin weld interface is formed between two aluminum plates.

P a t e n t Japanese Patent No. 6819959, Japanese Patent No. 6819958, Japanese Patent No. 6796839, Japanese Patent Application No. 2022-138404
Jeong-Won, Choi; Aoki, Yasuhiro; Ushioda, Kohsaku et al. Linear friction welding of Ti-6Al-4V alloy fabricated below β-phase transformation temperature.
Tr e a t i s e
Scripta Materialia. Volume 191, p. 12-16, doi: 10.1016/j.scriptamat.2020.09.013
UR
L http://www.jwri.osaka-u.ac.jp/~jthub/K e y w o r d linear friction welding, microstructural control, welding temperature, hardness distribution