Research On Mechanism Of Alumina Ceramic Reactive Metallization And Its Diffusion Brazing With 5a05 Alloy

The components of alumina ceramic and Al alloy are promising in electronic device, atomic energy industry, aerospace industry, and so on. However, the weldability of alumina ceramic and Al alloy are not good. Joining of alumina ceramic and Al alloy has to solve the poor wettability of ceramic and large residual stress in the joint which are the common problems in all ceramic and metal joining. Especially active brazing which is the main technique of joining ceramic and metal can't be used for the low melting point of Al alloy. To meet the requirement of joining alumina ceramic and Al alloy with high airtight performance, the new technique of alumina ceramic reactive metallization and its diffusion brazing with 5A05 alloy was put forward in this dissertation. The microstructure and forming mechanism of the joint were investigated and the whole processing was controlled to obtain alumina ceramic and 5A05 alloy components with good performance.Reactive metallization of ceramic was metallizing alumina ceramic with metal having active elements which can react with alumina ceramic and elements which can eutectic react with Al. After reactive metallization, the innerlayer on alumina ceramic interface was a continuous layer which provided good airtight performance. Using the outer layer which was metal solid solution having eutectic react with Al as the interlayer, the reactive metallized alumina ceramic was diffusion brazed with 5A05.Reactive metallization of alumina ceramic was the first step of joining alumina ceramic and 5A05 alloy. To get reactive metallized alumina ceramic with good performance, the reactive metal was designed and the effect of processing parameters was studied. The reactive metal was chosen as TiH₂ +AgCu eutectic+B mixture powder. The appropriate content of B was 0.9².3wt.% and the corresponding content of Ti was 5.8¹2wt.% for the joining of alumina ceramic and 5A05 alloy. The metallization temperature between 880℃and 900℃, the holding time between 5min and 20min were the optimized processing parameters resulting in the alumina ceramic/Ti₃Cu₃O/Ag(s.s)+Cu(s.s)+TiB+TiCu reactive metallization microstructure.The thickness of reaction layer on alumina ceramic interface had direct influence on the performance of alumina ceramic and 5A05 alloy joint. If the reaction layer was too thin, the joint airtightness couldn't be promised. And if the reaction layer was too thick, the defects such as crack would happen on the reaction layer itself. Based on analysis of the physical course of alumina ceramic reactive metallization, the relationship between factors which can be controlled in processing (such as the composition of reactive metal, metallization temperature, holding time and so on) and the thickness of reaction layer and AgCu solid solution was found.In the diffusion brazing of reactive metallized alumina ceramic and 5A05 alloy, the solution thickness of 5A05 alloy must be controlled. If the solution was too little, the oxide film couldn't be removed completely. And if the solution was too much, the erosion of the joint would happen. The 5A05/AgCu/5A05 system was investigated to illuminate the physical process of 5A05 alloy diffusion brazing and to establish the mathematical model aiming at providing theory guide for diffusion brazing of reactive metallized alumina ceramic and 5A05 alloy.Around the eutectic temperature Al-Cu-Ag ternary system was treated as Al-AgCu fake binary system and the concentration of Al was obtained. According to diffusion law and continuity equation, the motion of 5A05/AlCuAg liquid and AlCuAg liquid/AgCu alloy interface were analyzed. And the relationship of solution thickness of 5A05 alloy and diffusion brazing temperature, holding time, interlayer thickness was found.Based on the results of alumina ceramic reactive metallization and 5A05 alloy diffusion brazing, using the relation between reactive metallization outlayer and diffusion brazing interlayer thickness as the bridge, the controlling equations set of joining of alumina ceramic and 5A05 alloy was obtained. Considering the performance requirement and structure of alumina ceramic and 5A05 alloy components and aiming at controlling the thickness of reaction layer on alumina ceramic and 5A05 solution, the parameters such as content and amount of reactive metal, reactive metallization temperature, reactive metallization holding time, diffusion brazing temperature and diffusion brazing time were chosen to join alumina ceramic and 5A05 alloy. The mechanical and airtightness performance of the joint satisfied the application requirement.