Effect Of Sc Elements On The Properties Of Al-Si-Cu Filler Metal

The brazing of 6000 series heat-treated aluminum alloy has been the focus of research at home and abroad, the softening of parent material after brazing has not been properly solved, due to the lack of low melting point solders with good overall performance. Referencing binary and ternary phase diagrams of Aluminum and Aluminum alloy, the right amount of rare earth elements Sc was added in Al-8.5Si-20Cu-10Ge fill metal as the object of study. The filler metals’melting point, spreading behavior and their shear strength of the brazed joints have been tested and measured. The microstructure and phase composition of filler metals were analyzed with SEM, EDS. The results show that:The microstructure analysis of the solder showed that all the grains were effectively refined with the improvement of Sc addition to the Al-8.5Si-20Cu-10Ge alloy. The Al3Sc particles effectively functioned as the heterogeneous nucleation sites, and hence refined the as-casted grain sizes signifincantly. In addition, the Al3Sc particles strongly pinned up the dislocations and sub-grain boundaries, resulting in a stable sub-structure and gighly inhibiting the recrystallization of the alloy.With the addition of Sc, the mechanical property is improved significantly, compared with the joints without the Sc element, the joint strength could be up to 71.78MPa which is increased by 28.64% when the content of Sc is 0.1%.Within the range of this subject, the spreading area of the filler metals decline after rise with the addition of Sc. When the Sc content is up to 0.3%, the filler metal shows the best spread ability (844.25mm2). The spreading area will be reduced to 721.96mm2 with the Sc content to be 0.5%.Considering the liquidus temperature of solders, spread ability and mechanical properties, the sample of Al-8.5Si-20Cu-10Ge-0.1Sc in this experiment is best, with higher spread ability, grain refinement and the best characteristic of joint, which can be applied to vacuum brazing of 6063 aluminum alloy, and be promoted in the industrial field.