| The high strength aluminum alloy LY12 applicant in the structure of airplane,automobile and watercraft will reduce weight and synthetic properties. These advantages causes wide application. However, the current development and application of aluminum and aluminum alloys are restricted by its processing and low melting point. Applying proper welding technology, components with more complicated structure and larger size can be produced, thus expanding the application of high strength aluminum alloy. In this paper, low-melting filler metals for LY12 aluminum alloy were developed, which can be the foundation of aluminum alloy joining at a lower temperature.In this paper, Al-Si-Cu-Ge filler metals were prepared through crucible melting and flux protecting. Their melting characteristics, metallographic structure, spread abilities, wetting abilities, shear strength of the lap joints of the butt joints were measured through spreading and wetting capacity test, shear test as well as differential thermal analysis, optical microscopic structure inspection, SEM and energy spectrum analysis, X-ray diffraction analysis. The research results are as follows:1. Compared with Al-9.6Si-20Cu filler metal, the solidus and liquids temperatures of the filler metals added with the element Ge reduced a lot. The melting temperatures of the filler metals ranged from 407℃to 486℃, and the brazing temperatures were comparatively low, the highest of which was 510℃. The low temperature was conducive to the brazing with the lower melting point. The high frequency induction brazing equipment with self-designed argon protection device had received good effects, when being used brazing LY12 aluminum alloy.2. A large number of oversize primary precipitated phases of Si-Ge and Al2Cu(θ)in as-cast filler metals were found through the analysis of the metallographic structure of the filler metals. Thus generate several kinds of intermetallic compounds that cause the fragility of the metals increased largely. As the increase of wt.(Ge)%, the melting temperature decreases because of the increase of low melt point eutectic phase. Adding the element Ge, the wet abilities and spread abilities of the filler metals were comparatively good, with the minimum wetting angle of 4.5°.3. The brazing filler metals show good performance and no deficiency, which can be found in brazing seam. There was no difference between the metallographic structure of the joints and the as-cast filler metals. The bases were allα-Al, around which were Si-Ge phase and Al2Cu(θ)brittle phase. These brittle structures showed unfavorable impact on properties of the joints. The lap joint of the 3# filler metal had the highest shear strength, which was 93MPa, up to 40% of the base metal. The fractures of the joints were all brittle fractures which extended along the brittle phase in the joints.4. The brazing joint of filler 3# obtained the maximum strength 99MPa under its optimal process parameters which were 0.2mm width of clearance and 60mm2 of overlap area. On the other hand, the influence of melting temperatures, wetting ability, microstructures, and the fragility is explored when adding Er on the base of 3# filler metal. It is found that the melting temperatures changed not so much; but the wetting ability increased while the shear strength of joint; and the microstructures changed a lot, for example, precipitation Si-Ge phase reduced and the other grain size refined.
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