Joining of dissimilar materials like stainless steel and aluminum is of special interest for automotive applications. Due to the different properties of these materials, suitable joining techniques are required. Brazing offers the possibilities to manufacture high performance joints in one step and at low joining temperatures. However, these joints often need to withstand a high number of high cyclic loads during application. Therefore, in addition to the monotonic properties, the fatigue behavior of the produced joints must be considered and evaluated. In the present work, specimens are manufactured by induction brazing using an AlSi10 filler and a non-corrosive flux. The mechanical properties are determined by tensile shear tests as well as in fatigue tests at ambient and elevated temperatures. The microstructure of the brazed joints and the fracture surfaces of the tested samples are investigated by SEM.

The study deals with the characterization of the relationship between the microstructure of the reaction zone and the mechanical properties in the brazed joints of aluminum alloy 3003 and stainless steel AISI 304 in order to determine the influence of the intermetallic layers on the tensile shear strength of the joints. The joints were produced by induction brazing using an AlSi10 filler in an argon atmosphere at a temperature of 600 °C. Due to the local heat input into the liquid brazing filler during a short brazing time, a thin reaction zone is formed in the brazed joints (~1 µm), which ensures good mechanical properties of the joints. In order to observe the growth kinetics of the reaction zone in the brazed joints and to investigate the influence of the thickness of the reaction zone on the mechanical properties of the brazed joints, the joints were aged at temperatures of 200 °C and 500 °C for 6, 48 and 120 h. The results have shown that the thickness of this layer increases to a maximum of 2 µm depending on the duration of the thermal aging at a temperature of 200 °C. The results of the tensile shear strength tests have shown that the brazed joints with this thin layer ensure a high strength. The thermal aging at a temperature of 500 °C influences the growth of the reaction zone in the brazed joints significantly. The total thickness of the reaction zone increases to a maximum of 12 µm during the thermal aging. The results of the tensile shear tests of these joints have shown that the thermal aging at a higher temperature leads to a decrease of the tensile shear strength of the brazed joints to 67% due to the growth of the existing intermetallic layer and the formation of a new intermetallic layer in the reaction zone.

There is a requirement to combine different materials such as aluminum and stainless steel in industrial applications like automotive heat exchangers. Brazing offers the possibility to reduce the joining temperature in comparison to welding due to the lower liquidus temperature of the fillers. In the present work, the mechanical and microstructural behavior of aluminum / stainless steel mixed joints is investigated. The specimens are produced by induction brazing using an AlSi10filler and a non-corrosive flux. To evaluate the mechanical properties of the joints, tensile tests at elevated temperatures are carried out. Additionally, long-term thermal exposure experiments are done in order to investigate the changes in the microstructure.

Aluminum alloys based on the Al-Ge-Si system with a germanium content of up to 40 wt.%, promising for the brazing of aluminum alloy AA6082 with the stainless steel AISI 304, were studied. The temperature characteristics and microstructural and mechanical properties of the filler alloys were systematically investigated. Differential scanning calorimetry showed that with an increase in the germanium content from 28.0 to 40.0 wt.%, the liquidus temperature of the filler alloys decreased from 514.8 to 474.3 °C. X-ray diffraction analysis and electron microscopy data showed that the foil of the filler alloys reveals a homogeneous structure. The ingots of the alloys contain two eutectics, the first of which consists of a solid solution of (Al, Ge) with a solid solution of (Ge, Si), and the second consists of a solid solution of (Al, Ge) with a solid solution based on (Ge). When the content of germanium increases from 28.0 to 40.0 wt.%, a separation of the faceted solid solution particles (Ge, Si) and an increase in their number could be observed. Nanohardness measurements showed that the (Ge, Si) and (Ge) solid solutions had similar nanohardness, with values of 11.6 and 10.2 GPa, respectively. Simultaneously, the Al solid solution and the intermetallic Al₇Ge₂Fe phase exhibited significantly lower nanohardness values of 0.7 and 6.7 GPa, respectively. Brinell hardness measurements showed that the ingots of the filler alloys were sufficiently ductile and had a hardness comparable to that of AA6082, which is used for brazing with AISI 304 stainless steel. The obtained results for the studied ingots and the rapidly quenched foils can be used to predict the forming structure of the seam after brazing and adjusted for diffusion processes occurring between the brazed materials and the studied filler alloys.

In many industrial sectors, for example, aerospace, automotive and high-performance electronic industries, there is a significant need to join dissimilar materials. In the case of medium-strength aluminum alloys, joints are commonly manufactured using Al-Si brazing fillers with a melting temperature of 575 °C. In comparison to medium-strength aluminum alloys, high-strength aluminum alloys exhibit lower melting temperatures. Therefore, the joining possibilities are limited. Due to the lower melting temperature of about 500 °C, Al-Ag-Cu brazing fillers allow the joining of these alloys. In this study, high-strength aluminum alloys/stainless steel joints were produced via induction brazing and vacuum furnace brazing. The mechanical properties of the joints were determined using tensile shear tests as well as fatigue tests at ambient temperature. The joints produced via induction brazing at 520 °C without holding time reached a maximum tensile shear strength of 32 MPa. The joints failed in the braze metal close to the reaction zone. The joints brazed in the vacuum furnace at 540 °C for 10 min reached a maximum tensile shear strength of 18 MPa. The fractures occurred in the reaction zone, especially inside the Al₇Fe₂Si intermetallic layer. The thickness of the intermetallic layers as well as the reaction zone had a significant influence on the joining strength and the fracture mechanism of the brazed joints. The results of the fatigue tests showed that the joints brazed without holding time achieved the defined limited number of cycles of 1 × 10⁷ at a stress amplitude of 4 MPa. For all the fatigue-tested samples, the fracture occurred in the braze metal, especially in the eutectic. Hence, the reaction zone does not significantly influence the fracture mechanism of high-strength aluminum alloy/stainless steel brazed joints during cyclic loading.