In this paper, the effect of Cu element on the baking resistance of 8011 alloy aluminum foil was studied by tensile test, pinhole inspection, metallographic test, and baking resistance. The results show that after the baking experiment at 275 ℃ /75s, within a certain range, the high temperature stability of 8011 alloy is improved with the increase of trace Cu content in 8011 alloy.
Tags: 8011 alloy; Cu element; bake resistance
1 trial
1.1 Test material
The 8011 alloy casting and rolling billets were selected as the test materials, and the billet was 7.4mm*1140. The Cu content of the three 8011 alloys (8011-1, 8011-2, 8011-3) was different, and the composition of other elements was not very different.

1.2 Test plan
The aluminum foil production process flow is: smelting – casting and rolling – cold rolling – intermediate annealing – trimming – foil rolling – slitting – packaging.
Except for the difference in Cu content, the other production processes of the three 8011 alloy aluminum foils are produced according to the same process parameters. The obtained finished aluminum foil was tested for performance and baking test performance respectively. In addition, samples were taken for annealing test at 180 ℃, 200 ℃, 220 ℃, 240 ℃, 260 ℃ and 280 ℃ for 3h.

The pinhole and dyne value test of aluminum foil is tested according to the provisions of GB3198-2010. The three alloy finished samples obtained were placed in the same muffle furnace for baking tests. According to the actual use requirements of customers, the temperature of the baking resistance test is set to 275 ℃, and the baking time is 75s.
Tensile specimens are performed in accordance with GB3198-2010 standard, the gauge length is 100mm, and the long axis of the specimen is parallel to the rolling direction. Tensile specimens were tested on a KD II-1 electronic universal testing machine.

2 Test results and analysis
The three alloys have uniform structure and no internal structure defects such as segregation. The grain sizes of the three alloys are not much different, and the grain size is about 150 μm, which meets the requirements of the cold rolling process and annealing process of aluminum foil substrates.

In order to study the effect of Cu content on the properties and baking resistance of aluminum foil, three kinds of 8011 alloy aluminum foil products with different Cu content were tested for mechanical properties and baking test performance of finished products. The three 8011 alloys all underwent the same cold rolling, intermediate annealing, and foil rolling passes to obtain finished aluminum foils of the same thickness. The tensile strength of the alloy showed an increasing trend with the increase of Cu content. After the baking experiment, the tensile strength of 8011-3 alloy with higher Cu content decreased by 24.1%, the tensile strength of 8011-2 alloy decreased by 30.9%, and the tensile strength of 8011-1 alloy decreased by 33.3% . It can be seen that with the increase of Cu content, the performance stability of the alloy after baking tends to increase.

In the baking experiment, since the baking resistance of aluminum foil is closely related to the recrystallization behavior of the alloy, in order to compare and study the recrystallization behavior of the three 8011 alloys, the three 8011 alloy finished products were subjected to 180 ℃, Annealing at 200 ℃ , 220 ℃ , 240 ℃ , 260 ℃ , 280 ℃ for 3h, the results show that the annealing stability of 8011-3 alloy is higher than that of 8011-2 and 8011-1 alloy, 8011 at the same annealing temperature and time. -3 alloys have less recrystallization and softening degree.

In addition, we also conducted dyne value test and pinhole test on three 8011 alloys. The test results show that the dyne value and pinhole number of the three alloys all meet the standard.

For the 8011 alloy, within a certain range, with the increase of the trace alloying element Cu content, the solid solution strengthening effect is greater, so the strength of the 8011-3 alloy finished product is higher than that of the 8011-2 and 8011-1 alloys.

Cu can form a small amount of CuA12 compound by solid solution precipitation in aluminum alloy. The CuA12 compound has an irregular and smooth shape, and is intermittently distributed in the grain boundary in a skeletal shape, which plays a role in dislocation pinning in the subsequent aluminum foil processing and deformation process; the reason is that Cu mainly exists in the form of solid solution in Al, and they are easy to accumulate around dislocations. The formation of Coriolis air mass reduces lattice distortion, reduces the elastic interaction between solute atoms and dislocations, makes dislocations in a relatively stable state, reduces the number of movable dislocations, hinders the recombination of dislocations, and hinders the recombination of dislocations. Crystal nucleation and nucleation grow, thereby increasing the alloy strength and recrystallization temperature of the finished aluminum foil.

Second, trace amounts of Cu elements may also form secondary phases, which hinder the interfacial migration of recrystallized nuclei and hinder the growth of recrystallized grains. In short, within a certain range, increasing the content of trace alloying element Cu can increase the recrystallization temperature of the alloy and improve the heat resistance stability of the alloy. It can be seen that microalloying is one of the important ways to improve the heat resistance of alloys.

3 Conclusion
1) The 8011-3 alloy and 8011-2 alloy after increasing the Cu content can meet the requirements of customers in terms of finished mechanical properties, surface dyne, and the number of pinholes.
2) With the increase of Cu content, the tensile strength of 8011 alloy gradually increases; at the same time, the recrystallization temperature of the alloy also increases gradually.
3) After the baking experiment at 240 ℃/75S, the tensile strength of 8011-3 alloy with higher Cu content decreased by 24.1%, and the tensile strength of 8011-2 alloy decreased by 30.9%; Tensile strength decreased by 33.3%. 8011-3 alloy shows less variation in properties than 8011-2 and 8011-1. Increasing the Cu content helps to improve the baking resistance of the finished aluminum foil.