Microstructure and phase constituents in the interface zone of Mg/Al diffusion bonding
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INTRODUCTION
MAGNESIUM and aluminum are used in a wide variety of aerospace structural applications due to some unique performances such as low density, high specific strength, and good plasticity. For example, they are considered as advanced materials applied to parts in the automotive and aerospace industries, where lightweight metals are needed to minimize weight or to reduce the stress at high accelerations.[1,2,3] The refractory oxide film of Mg and Al forms inclusions in the heat-affected zone. Since the Mg has obvious thermal brittleness, the fusion welding of dissimilar materials such as Mg/Al is difficult. The test indicates that distortion and cracks in the heat-affected zone of Mg can be produced.[4,5] Vacuum diffusion bonding has increasingly made progress with the development of the computer and vacuum techniques, and it is used in joining brittle and dissimilar materials. The cracks, distortions, and segregation produced using fusion welding can be avoided. The dissimilar materials of Ti/Al and Al/18-8 stainless steel were bonded successfully by means of vacuum diffusion bonding, and the microstructure of the bonded joint was analyzed.[6,7] At present, the diffusion bonding of Mg/Al active metal has not been reported, so it is necessary to study the diffusion bonding and microstructure of Mg/Al dissimilar materials. In this article, the vacuum diffusion-bonded joint of Mg/Al dissimilar materials is analyzed. The microstructure, fracture morphology, and phase constituent near the interface of Mg/Al diffusion bonding are analyzed by scanning electron microscope (SEM), microhardness test, electron probe microanalyzer (EPMA), and X-ray diffraction (XRD). The relationship between technological parameters, microstructure, and joint performance was obtained by observing the microstructure and analyzing the new phase PENG LIU, Graduate Student, YAJIANG LI, Professor, JUAN WANG, Instructor, HAIJUN MA, Graduate Student, and GUOLIN GUO, Graduate Student, are with the School of Materials Science and Engineering, Shandong University, Jinan 250061, People’s Republic of China. Contact e-mail: [email protected] HAORAN GENG, Professor, is with the School of Materials Science and Engineering, Jinan University, Jinan 250022, People’s Republic of China. Manuscript submitted September 21, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS B
constituent. This is important for enlarging the application of the clad structure of Mg/Al dissimilar materials.
II.
EXPERIMENTAL
A. Equipment The vacuum diffusion bonding equipment, type WorkhorseII, was used in the test. The main parameters of the equipment are size of vacuum chamber 305 3 305 3 457 mm, heating power 45 KVA, highest temperature 1350 °C, maximum pressure 30 tons applied through hydraulic pressure, and vacuum degree 6.5 3 10ÿ4 Pa. The vacuum system is composed of the mechanical pump and the diffusion pump. B. Materials The materials in the test were magnesium (Mg 1) and aluminum (1070A). The diameter of the test bar was 60 mm, and the thickness was 6 mm. The s
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