Effect of Brazing Temperature on Microstructure, Tensile Strength, and Oxide Film-Breaking Synergy of 5A06 Aluminum Alloy Welded by TG-TLP

Abstract

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy.