Effects of Annealing and Deformation on Sagging Resistance of a Hot‐Rolled, Four‐Layered Al Alloy Clad Sheet

Abstract

Multilayer brazeable aluminum alloy sheet is prone to collapse during high-temperature brazing process. The sagging resistance of the aluminum composite sheet needs to be further improved for quality control. Effects of annealing and rate of reduction on sagging resistance, microstructure, and Si diffusion of a hot-rolled, four-layered Al clad sheet (4343/3003/6111/3003) were investigated by means of a sagging device, OM, SEM, and TEM. Results showed that once annealed at 360°C, the sagging distance was increased from 3 to 15.7 mm as the reduction rate changed from 10% to 40%. By increasing annealing temperature to 410°C, those were changed from 3.1 to 20.8 mm accordingly. At 360°C/40% and 410°C/40%, specimens exhibited weak sagging resistance, whereas fine recrystallized grains were formed in the core promoting Si penetration along grain boundaries. While the specimens were treated at 360°C/10% and 410°C/10%, better sagging resistance was observed due to the formation of coarse recrystallized grains that can suppress erosion of Si. At the same reduction rate, the sagging resistance was higher for the sample annealed at a lower temperature as more precipitates appeared in the core (at 360°C), thus leading to an increase in strength.

High-Temperature Mechanical Properties and Microstructure of Ultrathin 3003mod Aluminum Alloy Fins

“…In the manufacturing of heat exchangers, it is necessary that the fin material maintain a certain mechanical strength at a maximum brazing temperature of about 600 • C in order to prevent sagging and deformation, or even cracking during brazing [6,7]. At such high temperatures, aluminum alloys will inevitably undergo phenomena such as recovery, recrystallization, grain growth, second phase particle growth, particle redissolution, intergranular erosion, and slip deformation at grain boundaries, leading to a sharp decline in their mechanical properties [6][7][8][9][22][23][24]. On the other hand, grain boundaries show viscosity at high temperatures, which greatly reduces the resistance to deformation [25].…”

“…On the one hand, good mechanical and sagging resistance properties could be obtained through the optimization of the processing technology. Broer [4] revealed that the mechanical properties resulting from homogenization at lower temperatures could show an increase of approximately 40% compared to the reference homogenization at 550 • C. Kang [9] studied the effects of annealing and deformation on the sagging resistance of 4433/3003/6111/3003 clad sheet, and the results show that low-temperature annealing and a small amount of coarse recrystallized grains could suppress the erosion of Si, resulting in better sagging resistance and strength. On the other hand, alloying to produce dispersed and high-temperature-resistant fine particles is also an effective method to improve high-temperature strengths [11][12][13]26].…”

“…At present, the thickness of the aluminum alloy foil used in commercial fins is usually 0.07 mm, and the lightweight demands require the fin thickness to reach 0.05 mm or even thinner. After the aluminum alloy fin is thinned, the thickness of the supporting material decreases accordingly, resulting in a decrease in the load that the fin can withstand, and it can easily sag and delaminate during brazing at around 600 • C [5][6][7][8][9]. Therefore, improving the high-temperature properties and reducing the thickness of fins has always been the goal of this type material.…”