# Effect of Sc and Zr microalloying on recrystallization behavior of 1xxx aluminum heat exchanger alloys during post-deformation annealing

## TL;DR

This paper studies how adding small amounts of Sc and Zr affects the microstructure of aluminum alloys during high-temperature annealing, which is important for heat exchanger applications.

## Contribution

The study reveals the enhanced recrystallization resistance of 1xxx aluminum alloys through Sc and Zr microalloying, particularly at high brazing temperatures.

## Key findings

- The Al-0.19Sc-0.15Zr alloy showed the highest resistance to recrystallization due to fine Al3(Sc,Zr) precipitates.
- Al-0.07Sc-0.10Zr retained grain stability up to 550°C but partially recrystallized at 575°C.
- The base alloy fully recrystallized at 500°C and experienced abnormal grain growth at higher temperatures.

## Abstract

1xxx-series aluminum alloys are widely utilized in heat exchangers. During brazing, heat exchanger components are exposed to a short period of high temperature, which may trigger recrystallization and abnormal grain growth, ultimately compromising their mechanical properties. This study investigates the impact of Sc and Zr microalloying on the microstructure stability of hot deformed 1xxx alloys subjected to post-deformation annealing from 500 to 575 °C for 1 h to simulate brazing-type processes. Four alloys were studied: namely 1xxx base, Al-0.07Sc, Al-0.07Sc-0.10Zr and Al-0.19Sc-0.15Zr alloys. Annealing at 500 °C led to complete recrystallization in the base alloy, while higher annealing temperatures promoted abnormal grain growth. The Al-0.07Sc alloy resisted recrystallization at 500 °C but was fully recrystallized by 550 °C. In contrast, the Al-0.07Sc-0.10Zr alloy retained its grain stability up to 550 °C owing to the presence of stable Al3(Sc,Zr) precipitates; however, partial recrystallization occurred at 575 °C. The Al-0.19Sc-0.15Zr alloy preserved most of deformed microstructure even after annealing at 575 °C. It showed the highest recrystallization resistance among the four alloys studied owing to its highest number density and finest size of Al3(Sc,Zr) precipitates, which suggests that this alloy can be applied in even more extreme conditions including brazing temperatures above 575 °C.