Research On TIG Welding-brazing Process And Mechanism Of Al/Cu Dissimilar Alloys

In recent years, in order to alleviate the shortage of copper resources, while reducing production costs, Al/Cu composite structural elements develop rapidly to substitute some pure copper elements. Recent studies have shown that good properties of Al/Cu dissimilar metal joints can be obtained by welding-brazing. Welding-brazing can take full advantage of the large difference between the melting point of aluminum and copper. Through controlling the welding heat input aluminum base metal which has lower melting point can be melted but the melt of copper base metal is avoid as far as possible, because copper has higher melting point and heat conductivity. Dissimilar metals welding of aluminum and copper is realized which featured fusion welding joint at the aluminum side while brazing joint at the copper side. Welding-brazing is expected to be used in the welding of Al/Cu dissimilar metals.In this paper TIG welding-brazing of5052aluminum alloy and H62brass pieces lap joint is studied. Zn-2%Al and Al-12%Si flux-cored wire are selected as filler material. Process parameters are determined by welding tests first. Then the effect of different welding heat inputs on the microstructure and mechanical properties of the weld is studied by changing the welding current based on the simple variable method. Moreover the formation mechanism of Al/Cu welding-brazing interface layer is presented in according to the structure and phase composition of weld interface.Filling Zn-2%Al flux-cored wire, blocks and strips of CuAl2IMC are formed in the transition zone near interface layer which increase the brittleness of joint. Interface layer is consist of three kinds of IMC phases. Firstly, CuAl IMC layer precipitates at the interface. Then as for the dissolution and diffusion, Cu9Al4IMC layer is formed between CuAl layer and the copper base material. Due to the decrease of the copper content in the base material CuZn layer is obtained between Cu9Al4layer and the copper base material in the end. The interface layer will be thickened with increasing heat input within limits as a result of more intensive dissolution and diffusion. But when the heat input reaches a certain level, the thickness of interface layer decreases with further increase of heat input within a suitable range. The reason is that element concentration gradient at the interface layer declines because of increased amount of molten copper parent metal that inhibits the dissolution and diffusion process. The decrease of the interface layer thickness can improve the mechanical properties of joint. Welding-brazing joint of Al/Cu with certain mechanical properties can be obtained by controlling the welding heat input which can limit the formation of IMC phases near the interface layer at copper side.Filling Al-12%Si flux-cored wire, larger size strips of CuAl2IMC are formed in the transition zone near interface layer because of the high Al content in the filler material and partial melting and dissolving of copper base metal. The formation of CuAl2IMC strips severely weaken the mechanical properties of joint. The interface layer at copper side is consisted of two kinds of IMC phase layers. From the weld to the copper base metal is distributed Cu9Al4and CuZn. Due to the high Al content, no significant CuAl layer is observed in the interface layer as when Zn-2%Al flux-cored wire is filled. High-quality welding-brazing joint is difficult to be obtained due to the bad surface wettability of molten weld metal on copper.