| Reducing the weight down for lowing the fuel consumption, reducing the exhaust emission and improving the efficiency of automobile has become a tendency, which makes aging-hardenable Al-Mg-Si-Cu alloys as automotive body panels be widely concerned. Hot rolling, cold rolling and heat treatment must be done before stamping, and, the higher strength shall be gotten in subsequent paint baking process. The microstructures in sheets can affect their forming properties, tensile properties and serving capabilities, and how to use microalloying and suitable heat treatment processes to influence microstructures, sequently get the combination of suitable mechanical properties and excellent forming properties and obtain the final desired strength after aging processing, which is the goal for the material researchers at all times. In this paper, on the basis of Al-Mg-Si-Cu alloy, effects of Sr, different heat treatment processes during rolling and different aging processes after solution treatment on the texture component and properties have been researched systematically and the relationship between the textures and the properties has been found by using modern analytical techniques such as optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope(SEM) and electron backscatter diffraction technique (EBSD).1. Effects of Sr on microstructures and properties of Al-Mg-Si-Cu alloy sheetsThe textures investigation about 2.5mm sheets indicates that the basic types of textures do not change and the f(g) of textures changes because of addition of Sr. The maximum f(g) lies at the site near{011}<211> in the alloys with no or 0.033% Sr (mass fraction, the same below) addition; the maximum f(g) lies at the site near {112}<111> in the alloy with 0.093% Sr.In the Sr-free alloy, there are rotation cube texture and fibre texture, and the bulk percentage is 21.2% and 38.8% (bulk percentage, the same below), respectively. The characteristics of textures in the alloy with 0.033% Sr addition have no significant difference from those in the Sr-free alloy, and the textures content decreases slightly, the bulk percentage of the rotation cube texture and the fibre texture is 18.7% and 35.6%, respectively. The characteristics of textures in the alloy containing 0.093% Sr differ obviously from those in the two above-mentioned alloys, the bulk percentage of the rotation cube texture and fibre texture is 0.024% and 1.2%, respectively, in the former alloy.The textures investigation about 1.0mm sheets indicates P orientation {011}<122> and S1 orientation{124}<211> with strong f(g) exist in the alloy with no Sr addition; Orientation with strong f(g) near to the orientation{011}<011>, Cu orientation{112}<111> with very strong f(g), B orientation{011}<211> exist in the alloy with 0.033% Sr addition; Orientation{011}<111>, S3 orientation{123}<634> and B orientation{011}<211> exist in the alloy with 0.093% Sr addition.Experiments show that the tensile strength Rm, the yield strength Rpo.2, the elongation A, the strain hardening exponent n, the plastic strain ratio r and the cupping value of the sheet with 0.033% Sr addition are 360MPa,200MPa,23.3%, 0.296,0.729 and 8.13mm, respectively.By analysing the relationship between the performance and the textures of the alloys, some results will be achieved that the ratio of the rolling textures to the recrystallization textures is 0.02, the fraction of the random orientation is 76.4% and the mechanical properties and the forming properties are best in the alloy with 0.033% Sr addition among all alloys. The ratio of the rolling textures to the recrystallization textures is 1.97 in the alloy containing 0.093% Sr, now the performance is the same as that in the alloy without Sr. These results indicate relative small ratio of the rolling textures to the recrystallization textures is conducive to the performance of the alloy.2. Effects of mid-annealing processes on microstructures and properties of Al-Mg-Si-Cu alloy sheets.The textures investigation about 2.5mm sheets indicates that the types of the textures are same basically, and mainly R-Cube orientation{001}<110>, weaker B, S and C orientation exist in the alloys with no mid-annealing process and 350℃for 1h mid-annealing process. The f(g) of R-Cube orientation, B, S and C orientation in the alloy mid-annealed at 510℃for 1h is much lower than that in the two above-mentioned alloys. The bulk percentage of R-Cube and fibre component in the alloys with no mid-annealing process,350℃for 1h mid-annealing process and 510 ℃for 1h mid-annealing process are 21.2%,38.8% and 19.8%,37% and 13.7%, 31.2%, respectively.The textures investigation about 1.Omm sheets indicates that in the alloy without mid-annealing process, there are deflected G orientation with relative strong intensity, Q orientation and residual rolling C orientation. In the alloy mid-annealed at 350℃for 1h, there are G orientation with very strong intensity, Q orientation and R/S orientation. In the alloy mid-annealed at 510℃for 1h, there are deflected G orientation with relative weak intensity and R/S orientation. Fibre component{111} exists in all alloys, and is more bulk percentage in the alloys with mid-annealing process.Performance tests show that the tensile strength of alloys drops and the elongation of the alloys increases with mid-annealing temperature increased. The n,r and Cup value of the alloys with no mid-annealing process,510℃for 1h mid-annealing process are 0.269,0.729,8.13mm and 0.311,0.788,8.98mm respectively, the n,r and Cup value are 0.310,0.774 and 8.77mm respectively in the alloy mid-annealed at 350℃for 1h, and falls in between those of the two former alloys.Analysis of the relationship between the textures and the performance indicates that the ratio of the rolling textures to the recrystallization textures is 0.029,0.036 and 0.036 in the alloys with no mid-annealing,350℃for 1h mid-annealing and 510℃for 1h mid-annealing, respectively. The fraction of random orientation is 76.4%, 64.7% and 56.6%, respectively, so the performance of the alloys are not different obviously in three alloys.3. Effects of aging processes on microstructures and properties of Al-Mg-Si-Cu alloy sheets.There are Cube orientation with very weak f(g), B orientation with weak f(g), R/S orientation and special Q orientation appeared when high reduction in the alloy with no aging treatment. PSN effect is very strong, and there are G orientation with very strong f(g), Q orientation and R/S orientation in the alloy aged at 150℃for 5min. There are relative strong deflected Cube orientation and Q orientation in the alloy aged at 150℃for 30min. More{111} orientation exists in all three alloys. Performance tests show that the elongation, n,r and Cup value of the alloys with no pre-aging process and 150℃for 5min pre-aging process are 17%,0.273, 0.701,7.89mm and 25%,0.310,0.774,8.77mm respectively. The tensile strength and the yield strength improve significantly, and are up to 360MPa and 210MPa respectively, however the elongation, n,r and Cup value are down to 19%,0.284, 0.733 and 8.21mm respectively in the alloy aged at 150℃for 30min.Analysis of the relationship between the textures and the performance indicates that compared to others, the ratio of the rolling textures to the recrystallization textures is 2.5, and the forming performance and the tensile performance are lowest in the alloy with no aging treatment; the ratio of the rolling textures to the recrystallization textures is minimum, and the forming performance is best in the alloy aged at 150℃for 5min.Performance tests and analysis indicate that the general performance is best in the alloys, which has 0.033% Sr addition, is mid-annealed at 350℃for 1h, aged at 150℃for 5min after solution treatment, as follow:tensile strength Rm for 340MPa, yield strength Rpo.2 for 180MPa,n value for 0.31, r value for 0.774 and cup value for 8.77mm. |
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