| The effects of super-plastic pre-treatment (SPPT) and cold rolling before aging on the microstructure and mechanical properties of the 7A04 and 2024 Al alloys were investigated by means of optical microscope, mechanical tensile test, EBSD analyse, SEM and TEM observations. The relations of the microstructure and mechanical properties were discussed also. The conclusion can be drawn as the following:1. The average grains size of 7A04 alloy by SPPT is Hum, however that by conventional treatment(CT) is 30μm. The SPPT improves the ultimate tensile strength by 3.5%, and elongation to failure by 25.7% . The average size of grains by SPPT is smaller than one by CT. The enhancement in plasticity is attributed to refinement of grains.2. 7A04 alloy obtains the optimal combination of strength and ductility in such solid solution and recrystallize treatment: 470℃ ×5min+480℃× 12min, the contradiction on dissolution of overageing phases and growth of new grains was settled also by it. The tensile strength is 585MPa and elongation to failure is 17.6%.3. As the overaging temperature in the SPPT increasing, the strength of 2024 alloy also improving. When the over-aging temperature obtains 350℃,the alloy performance is superior. There are two peaks in the curve of tensile properties, the first peak appears when the ageing time is 40min. When the aging time is 120min, the second peak appears, at the moment the main second phase is S'.4. The performance of 7A04 alloy by cold rolling before aging is degenerated when compared with 2024 alloy, it is mainly because the coarsening of grain of 7A04 alloy in the dislocation is severer than 2024 alloy, so the properties of 2024 alloy is predominant. |
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