# Microstructure and Mechanical Properties of 7072 Aluminum Alloy Joints Brazed Using (Ni, Y)–Modified Al–Si–Cu–Zn Filler Alloys

## TL;DR

Researchers developed a modified aluminum filler alloy that improves the strength and ductility of brazed joints in high-strength aluminum alloys.

## Contribution

A (Ni, Y)-modified Al–Si–Cu–Zn filler alloy is shown to enhance joint strength through microstructure refinement and phase transformation.

## Key findings

- Ni lowers the liquidus temperature and converts brittle Al2Cu into ductile Al2(Cu,Ni), improving joint strength.
- Y promotes nucleation and microstructure refinement, enhancing mechanical properties.
- A 2.0 wt.% Ni and 0.4 wt.% Y filler achieved a peak tensile strength of 295.1 MPa in brazed joints.

## Abstract

Aluminum–based brazing alloys have been developed for joining 7072 high–strength aluminum alloys. However, challenges related to their high melting points and joint softening still require further exploration. This study employs a combination of first–principles calculations and experimental techniques to examine the microstructure and mechanical properties of 7072 aluminum alloy joints brazed with (Ni, Y)–modified Al–Si–Cu–Zn filler alloys. Through the virtual crystal approximation (VCA) method, it was observed that the Al–10Si–10Cu–5Zn–xNi–yY (x = 0, 1.0, 2.0, 3.0, y = 0.2, 0.4, 0.6) filler alloy exhibits excellent mechanical stability, combining both high strength and reasonable ductility. Seven brazed joint samples with varying Ni and Y contents were fabricated using melting brazing and analyzed. The findings showed that Ni reduces the liquidus temperature of the filler, narrowing the melting range. This facilitates the conversion of the brittle Al2Cu phase into a more ductile Al2(Cu,Ni) phase, thus enhancing joint strength. Y acts as a heterogeneous nucleation site, promoting local undercooling, increasing the nucleation rate, and refining the microstructure. When the Ni content was 2.0 wt.% and the Y content was 0.4 wt.%, the tensile strength of the brazed joint reached a peak value of 295.1 MPa. Computational predictions align with the experimental results, confirming that first–principles calculations are a reliable method for predicting the properties of aluminum alloy brazing materials.