To meet the lightweight demands of automobiles, Al composite sheets require excellent mechanical properties under the condition of minimal thickness after high-temperature brazing processing. Generally, the standard used Al brazing sheets have a low strength before and after brazing. To overcome this issue, this work develops a novel 4343/3003/6111/3003 four-layer Al clad sheet, whose microstructure and mechanical properties are systematically investigated. The results show the observable fibrous microstructure with elongated grains parallel to the rolling direction in the developed four-layer Al clad sheet of the cold-rolled and annealed states. After brazing, this fibrous microstructure transforms into coarse equiaxed grains. In addition, the 4343 layer is the brazing layer. Si is mainly distributed in the 4343 layer of the cold-rolled Al clad sheets, whereas Si penetrates into the core layer along the grain boundaries after brazing. The cold-rolled samples present a certain brittleness from fracture morphology, whereas the final annealed ones show a typical ductile fracture. Meanwhile, the typical intergranular fracture is visible after brazing. The mechanical properties of the Al clad sheets are improved after brazing, with an increase of 76% in tensile strength and 62% in yield strength, compared with the final annealed ones. The elongation is increased by 29% compared with that of the cold-rolled ones. This study provides a theoretical basis for further improvement of the strength of aluminum honeycomb panels.

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.

Surface treatment has shown strong effects on the corrosion resistance of Al-Mg-Si-Cu alloys. To elucidate the surface grinding effects, a set of the peak-aged Al-Mg-Si-Cu samples are ground using SiC papers with different grits, and the ground surface microstructure and corrosion performance are investigated. The results show that grinding generates a deformed near-surface layer. The deformed layer is characterized by nanocrystalline and the alloying element Cu segregates at nano-grained boundaries. The Cu segregation bands increase the available cathode area and the potential difference between the grain boundary and grain interior, which enhances the microgalvanic corrosion effect between the phase α-AlFeSi (Mn, Cu) and the adjacent matrix. As the SiC paper grit number decreased from 1200 to 80, the Cu segregation bands of the deformed layers increases from 600 to 1600 nm, the corresponding corrosion current density increases from 1.0 ± 0.1 to 22.8 ± 0.7 μA.cm⁻², and the corrosion potential decreases from −742 ± 13.1 to −791 ± 15.0 mV (versus SCE).