Development Of A Al-Si Based Brazing Filler By Rapid Solidification Technology

Aluminum alloy has extensive application in engineering, but some welding problems needed to be solved still, such as poor welding properties, lower welding strength and high friability of welding seam. In this case, this paper has developed a kind of brazing filler based Al-Si alloy by rapid solidification technology. In order to improve the welding properties and welding strength of the brazing filler based Al-Si alloy, Cu, Zn and RE elements has been added and supersonic gas atomization technology has been used to prepare brazing filler powder. The major research work is as following.A series chemical composition of brazing filler based Al-Si alloy has been designed. The brazing filler powder has been prepared by supersonic gas atomization technology; the parameter of supersonic gas atomization technology has been studied by test. The microstructure characteristics of the brazing filler powder have been analyzed. The welding properties of the brazing filler have been studied by test. A kind of optimized chemical composition of brazing filler has been identified.The results show that the brazing filler powder has globular or near globular shape, concentrated grain size, the average grain diameter is about 0.12mm; The microstructure of the brazing filler powder is finer and the quantity of secondary phases is reduced compared with cast alloy. Zn and RE elements can reduce the melting point and the more the quantity of Zn element is, the more melting point reduced. When the quantity of Zn element reaches 20%, the brazing filler melting point is reduced to 518.9℃, which is a very good welding property. Cu element can raise the melting point of the brazing filler, therefore, its quantity should be limited in the brazing filler. The wetting property of the brazing filler is affected by adding of Zn and RE elements. The raising of Zn element can improve the wetting property of the brazing filler and RE element will increase the wetting property by removing oxidized film on the melted brazing filler. The analysis of brazing seam microstructure shows that the characteristics of rapid solidified microstructure are retained in still. RE element has the action to reduce microstructure size by changing eutectic Si phase shape from needle to granular. Therefore, RE element has the action of modification on eutectic Si phase. The strength of the brazing seam is affected by Zn and RE elements added, the more quantity of Zn element is, the higher strength of the brazing seam has. RE element can also increase the strength of the brazing seam. By synthesizing the properties of five kinds of brazing filler, an optimized chemical composition has been selected, that is Al-10Si-5Cu-20Zn+0.3RE.