Study Of Influence Of Heat Treatment On Microstructure And Properties Of 7A04 Aluminum Alloy

Aluminum alloy was widely used in aerospace aircraft, automotive, machinery manufacturing, chemical industry and vessel because of its low density, high specific strength, excellent conductivity and thermal conductivity, high corrosion resistance and good plasticity. The properties of the ultra-high strength aluminum alloy are due to its matrix microstructures and morphology and distributions of the second-phase precipitates affected by solution and ageing treatment. In order to obtain the excellent mechanical properties, it must be took the suitable solution-ageing treatment.In this paper, the mechanical properties of the ultra-high strength 7A04 aluminum alloy at different heat-treatment conditions, including solution, single-ageing, two-stage aging and three-stage aging, were investigated by room temperature tensile test, hardness and impact toughness test, neutral salt spray test and intergranular corrosion test. The microstructures were investigated by optical microcopy, laser confocal scanning microscope and transparent electron microscope. The results show that the optimal solution treatment is treated at 470℃for 1 hour. The amount of coarse second phases can be reduced effectively and the size of grain can be controlled. The mechanical properties of aluminum alloy can be greatly improved. The dispersive distribution of the second phases can be abtained by using three-stage aging treatment which has the best mechanical properties. At this condition, tensile strength, yield strength, elongation and impact toughness respectively reach 642MPa, 546MPa,13.5%, and 14J. It has been deduced the linear regression equation which could reflects the corresponding relationship between tensile strength and hardness: Yi=100.742+2.919Xi. Aluminum alloy treated by three-stage aging treatment can obtain the best resistance againt salt spray and intergranular corrosion, and aluminum alloy treated by single-ageing treatment the single-ageing treatment obtain the worst resistance againt salt spray and intergranular corrosion.After the results were analyzed and discussed theoretically, the heat-treatment processes were optimized.