Vacuum Brazing of 2017 Aluminum Alloy Using Al-Ge-Cu Based Fillers

Abstract

In the first step of the study, liquid surface around the ternary eutectic composition of Al-Ge-Cu system was surveyed by means of DTA to determine compositions of fillers having melting points lower than the solidus temperature of 2017 alloy. Auger electron spectroscopy (AES) analysis on 2017 alloy were also carried out to investigate the surface condition during the heating in brazing process.
Based on the results of aforementioned investigations, Al-Ge-Cu-Mg and Al-Ge-Cu-Si-Mg fillers were developed and employed in brazing experiment. Brazing was carried out in a vacuum of less than 2×10^-2 Pa at 773 K for 7.2 ks followed by diffusion treatment (solid solution heat-treatment of T4) at 773 K for 7.2 ks, 173 ks or 605 ks. Brazed specimens were then subjected to tensile test to evaluate the strength of the joints. 67% of joint efficiency was achieved in the specimen brazed with a Al-Ge-Cu-Si-Mg filler and diffusion treated at 773 K for 605 ks.
Electron probe micro-analysis (EPMA) performed across the brazed joints revealed that longer diffusion treatment promotes homogenization in microstructure between the filler and the base metal, which homogenization will account for the higher strength in the joints with longer diffusion treatment.