Effects Of Heat Treatment And Multi-direction Forging On Microstructures And Properties Of 7A04 Aluminum Alloy

In this paper,7A04 aluminum alloy was deformed by multi-direction forging at the temperature of 380℃～440℃for different passes. After multi-direction forging, annealing and solution together with aging treatment were also performed on the alloy. Optical microscopy (OM) was used to study the microstructures under different forging and heat treatment conditions, tensile testing machine was adopted to check the mechanical properties before and after the multi-direction forging, and scanning electron microscopy (SEM) was employed to observe the.morphology of tensile fracture. The microstructures and mechanical properties of 7A04 alloys with the change of multi-direction forging and heat treatment conditions were investigated to provide regular reference for the further study.With the increase of multi-direction forging temperatures and forging passes, the second-phases broke and dissolved, and it made for the dynamic recrystallization and the refinement of the microstructures. When it is forged for one pass, and the temperature is 380℃and 400℃, the mainly mechanism is dynamic recovery, and the dynamic recrystallization can not carry out sufficiently; as the forging temperature come up to 420℃and 440℃, the dynamic recrystallization occurs fully, and the grains are fine and isometric. When it is forged for two passes, the dynamic recrystallization can process sufficiently at the temperature of 380℃.In this experiment, the best forging temperature is 420℃,and the best forming process is two passes at the temperature of 420℃,the mechanical properties can be achieved:σb=552.2Mpa,σ0.2=463.6Mpa,8=18.77%.As for the other forging temperatures, the mechanical properties can achieve the optimum value after three passes of forging. Multi-direction forging can refine the microstructures of 7A04 alloy, increase its strength as well as keep the plasticity at a high level.Annealing after multi-direction forging decreases the hardness and strength of 7A04 alloy, but the distribution of microstructure becomes uniform and the inner stress is eliminated so that the plasticity is improved greatly. Among the different temperatures 390℃,410℃and 430℃, lower annealing temperature(390℃) can get the best comprehensive properties. Solution and aging treatments make the second phase dissolves into the matrix structure absolutely, increasing the strength while decreasing the plasticity at a small amount. In this experiment, the best comprehensive properties occur after 420℃multi-direction forging,solution at 485℃ was carried out for 45min, cooled by water, aging forl6h at 130℃,cooled in air, the mechanical properties can achieve:σb=595.8Mpa,σ0.2=511.5Mpa,δ=14.98%.