The effects of stable surface oxides on the interface morphologies and strengths of aluminium diffusion bonds are reviewed. Previous approaches, proposed to overcome problems with surface oxides when joining aluminium alloys and composites, are described and compared for both solid-state diffusion bonding and conventional transient liquid-phase diffusion bonding. Non-conventional joining methods, particularly the new method of temperature-gradient transient liquid-phase diffusion bonding and its capability of producing high-strength bonds reliably, also are considered. Copyright © 2001 John Wiley & Sons, Ltd.

Interface evolution and bond strength when diffusion bonding materials with stable oxide films

The work is entirely my own and includes nothing which is the outcome of work done in collaboration, except where reference is explicitly made to the work of others. The work has not been submitted, either in whole or in part, for any degree or qualification at any other university and does not exceed 60,000 words. Acknowledgement I am wholeheartedly grateful to my supervisor, Dr Rob Wallach, for his guidance, encouragement and invaluable friendship during my research period in Cambridge. It is a pleasure for me to acknowledge Dr Sue Jackson for her advice and ever friendly support. Also, I would like to thank Dr Ian Bucklow for the useful discussions I had with him on my work. I sincerely thank Dr Hamid Assadi for his advice and help throughout my research, and also Fataneh who provided an enjoyable atmosphere for Hamid and me to carry on with our discussions. I am also grateful to Mohammed Balamdi for " tidying " my room frequently and Kaveh Chamandar who kept correcting my English accent so patiently. Thanks are also due to my friends at King's College: Clea for her kind friendship and food-wise logistic; Liz, Ken, Kai and Paul for improving my knowledge to the single currency issue during our outings. laboratory facilities, and I express my gratitude to my research colleagues, academic and technical staff in the Department who helped me so sincerely in the course of my research. Finally, thanks to the staff in my college for their help and many others who made my time in Cambridge so enjoyable. Abstract Development of a suitable joining technique for advanced aluminium alloys and composites will enable them to be more widely used. The aim of this Ph.D. research was to develop new joining methods for these materials for which conventional welding methods have been unsuccessful. The research led to six new bonding methods and also to an analytical model which may be applicable to all transient liquid phase (TLP) bonding processes. In the early stage of the research, two new methods for TLP diffusion bonding of aluminium-based composites (aluminium alloys with silicon carbide particles as reinforcement) were developed. The methods were based on applying isostatic pressure (rather than conventional uniaxial compression), and bonds were fabricated with shear strengths as high as 242 MPa which is 92% of the shear strength of the parent material. This value is far greater than …

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Diffusion bonding aluminium alloys and composites : new approaches and modelling

Vibration liquid phase bonding for SiCp/A356 composites in air was investigated. Vibration can disrupt and extrude the oxide inclusion layer on the surface of the composites. The metallurgical bond between the filler metal and the matrix forms during vibration liquid phase bonding, and the tensile strength of the joints increase with the vibration time. During vibrating, the residual liquid filler metal layer in the joint is squeezed out, and mix with the base metal, the primary Zn–Al–Cu hyper-eutectic in the joints transforms into Al-rich Al-base solid solution (α-Al), a composite bond reinforced by original and broken-up SiC particle forms.

Interface structure changes during vibration liquid phase bonding of SiCp/A356 composites in air

The vibration liquid phase diffusion bonding of SiCp/A356 composite in air has been investigated. The surface of specimens to be bonded was treated with and without vibration under the bonding condition. It was found by atomic force microscopy analysis that some of the oxide film could be broken down when ridges on the surface of the matrix were ground down. Dissolution of the base metal by the filler metal occurred with removal of the oxide film during vibration liquid phase bonding, and SiC particles in the base metal entered the bond region. A removal process model for vibration bonding has been established with and without filler metal. Results show that shearing and impacting actions are the two main breaking mechanisms during vibration; the oxide film bulk is generally broken down by shear, and dissolution of the base metal by the filler metal promotes particle segregation from the matrix and their entry into the bond region.

Modelling behaviour of oxide film during vibration diffusion bonding of SiCp/A356 composite in air

Joining process: 'exploiting the diffusion of atoms present between the surfaces being bonded, involving base metals being brought into close contact and pressure being applied to a degree as far as possible avoiding plastic deformation under temperature conditions below the base metal melting point ' (from JIS Z 3001 'Welding terminology'). Diffusion bonding of aluminium has been well documented in papers presented at symposia and other conferences held by the Journal of Light Metal Welding and Construction. Figure I shows the process of increase in the bond area reflecting the degree to which diffusion bonding progresses.

T. Haseyama

Papers

Solid phase welding of alloy AA6061 and SiCp reinforced alloy AA6061 at intermediate temperature