Study On Microstructure And Properties Of AA8079 Foil Aluminium Alloy

Currently, the domestic 6~7μm light gauge foil production generally use AA1235 alloy, while it generally is AA8079 alloy in European and American factory. Compared with AA1235 alloy, the element content of Fe and Si in AA8079 alloy is higher, it has higher mechanical properties when used in the production of aluminium foil stock, and it can be used in a high speed when rolling without strip breaking, so it can raise the production efficiency of aluminum foil. Domestic aluminum foil processing enterprise, therefore, are beginning to use AA8079 to replace AA1235 for aluminum foil production, but is still in the exploratory stage, there are still many problems in the production process. The composition of AA8079 alloy has direct impacts on its microstructure and properties, therefore the study of the optimal content of Fe and Si in the alloy is very important; Improperly control of microstructures and second phases in the aluminium foil stock will affect subsequent rolling and the finished product properties, so study the evolution law of microstructures and second phases in the processing is particularly necessary.This paper selected the AA8079 alloy producted by continuous roll casting, studied the evolution law of microstructures and second phases in the AA8079 foil stock processing by a series of analysis methods such as optical microscope(OM), electron back-scattered diffraction(EBSD), X-ray diffraction(XRD), scanning electron microscope(SEM) with energy spectrum analysis(EDS); determined the recrystallization annealing process of AA8079 alloy by using differential scanning calorimetry(DSC), tensile testing and metallographic analysis. Analysed the performance difference between AA1235 and AA8079 aluminium foil and its causes through mechanical properties test and the statistics of strip breaking and finished product rate of pinhole.The main results are as follows:(1)Both the cast-rolled and cold rolled sheet that produced with the three kinds of alloy have streamlined deformed microstructure under processing state. After annealing, are completely recrystallized, their microstructure are transformed into recrystallized structure. There is no big difference between AA8079 alloy No.2 and 3 in the microstructure of cast-rolled sheet, but both of them have a smaller grain size than that of AA1235 alloy. Cold rolling processing will minimizing the disparity between them, but AA8079 alloy still has smaller and more uniform grain after heat treatment.(2) During processing, the degree of the misorientation angle deviating from the random distribution increase with the deformation level of the three kinds of sheet, when cold rolled to 3.9 mm, the grain orientation is focused on the < 001 > and < 111 > direction, and shows obvious preferred orientation, the fibrous tissue forms. The average grain size of the three kinds of cast-rolling sheet is 53.6μm, 48.6μm and 48.6μm.(3) Compared with AA1235, the second phase in AA8079 cast-rolling sheet has lager quantities, size and its distribution is more uneven. With cold rolling and annealing, the disparity will be minimized. The second phase in AA8079 aluminum foil stock became small, and uniformly distributed in the matrix while rolling to 0.24 mm. AA8079 alloy has a lager quantity of the second phase than that of AA1235 during the whole processing;(4) During processing, the species of the second phase in the three kinds of aluminum foil stock are basically the same, and all of them have large needlelike θ(Al3Fe) phase in the 3.9 mm sheet after annealing. Compared with AA1235,the θ phase in AA8079 aluminum foil stock has a higher content. With the process going the θ phase quantity reduced, gradually disappear, so more suitable for the subsequent foil rolling.(5) Study on the mechanical properties shows that the strength of the 2# and 3# cast-rolling sheets reached 130 MPa, elongation reached 41.3%, which higher than 2# alloy, are more suitable for high speed rolling. With the process going, the mechanical properties disparity of three kinds of alloy will be minimized. While rolling to finshed foil stock, all the tensile strength of them were 138 MPa, the elongation is approximately 3.2%.(5) Study on the properties of aluminium foil shows that,6.35μm aluminium foil produced by AA8079 has few times strip breakage and higher finisfed producted rate than that of AA1235.Properly control the pinhole rate, AA8079 can be used to produce thiner light gauge foil instead of AA1235.