Structure–Property Relationship in High-Strength Aluminum Alloys/Stainless Steel Brazed Joints

Abstract

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.