Structure-property relationship in high-strength aluminum alloys / stainless steel brazed joints using low melting Al-Ge-Si filler metals

S. Busse, V. Fedorov, S. Hausner, G. Wagner

In many industrial sectors, for example aerospace, automotive and high-performance electronic industries, is a significant requirement to join dissimilar materials. Especially for high strength aluminum alloys / stainless steel components, the joining possibilities are limited due to the low melting temperatures of these Al alloys. Low melting filler metals based on the ternary system Al-Ge-Si allow brazing of this material combination providing melting temperatures of about 500°C. High-strength aluminum alloy AA6082 / stainless steel AISI 304 mixed joints are produced by induction brazing and vacuum furnace brazing with varying process parameters using Al-Ge-Si brazing fillers of different stoichiometry. The reaction zones of these brazed joints are investigated by SEM and EDXS with regard to their microstructure. Additionally, the mechanical properties are determined by tensile shear tests at ambient temperature. Fatigue tests are carried out for the interconnects, produced by induction brazing. The results show, that high-strength aluminum alloys / stainless steel mixed joints with a thin reaction zone are possible. Its microstructure and thickness have a significant influence on the mechanical properties and the fracture mechanism of the braze seam. Joints produced by vacuum brazing only reached a highest tensile shear strength of 20 MPa. Maximum tensile shear strength of 53 MPa could be achieved for interconnects produced by induction brazing. These joints reached the limited number of cycles of 1∙10⁷ at a stress amplitude of 7 MPa.