| In this paper, Conventional 7075 aluminum alloy, the high Zn content 7075 aluminum alloy and the 7075 aluminum alloy containing Er and Ti were prepared by ingot metallurgy method. The mechanical properties of the above alloys were tested after the T6 treatment, two-step aging, retrogression and re-aging(RRA) treatment and two-step aging with one high temperature retrogression. Then the microstructure of 7075 aluminum alloy were observed and analyzed by metallographic microscope and scanning electron microscopy(SEM). The research mainly focused on the effect of RRA and a high temperature retrogression within the two-step aging on 7075 aluminum alloy though controlling the temperature or time to obtain the best aging process parameters. The results showed that:(1) The fatigue crack initiation life of Conventional 7075 aluminum alloy at T6 state treatment was 97193, and Intensity ratio(Rsb) of the alloy was 1.23 with181.6HV of hardness, 549 MPa of tensile strength and 6.4% of elongation. The best hardness of the Conventional 7075 aluminum alloy under the RRA treatment as120℃/16 h +190℃/10min+120℃/16 h was 182.5HV, a little higher than the conventional 7075 aluminum alloy under T6 state treatment. After introducing a high temperature retrogression into the the best two-step aging of the conventional 7075 aluminum alloy, we got the best aging process as 120℃/24h+200℃/5min+160℃/30 h. Aftre this treatment, the tensile strength was 565 MPa, increased by 2.9%and the elongation of the alloy was 9.6%, increased by 50% compared with the T6 state treatment.(2) After increased the Zn content in 7075 aluminum alloy, the grain was refined.The tensile strength of the high Zn 7075 aluminum alloy could be increased to 640 MPa, with 3.6% of the elongation and 201.2HV of the hardness under T6 state treatment. After a best RRA treatment as 120℃/12h+210℃/10 min +120℃/16 h, the hardness of the high Zn 7075 aluminum alloy increased to 215.7HV, increased by3.9% compared with the high Zn 7075 aluminum alloy under T6 state treatment,increased by 14.7% compared with the conventional 7075 aluminum alloy under T6 state treatment. After introducing a short high temperature retrogression into the the best two-step aging of the high Zn 7075 aluminum alloy, we got the best aging process as 120℃/24h+220℃/10min+160℃/30 h, while the tensile strength was588 MPa and the elongation was 11.5%, increased by 219% compared with the high Zn 7075 aluminum alloy under T6 treatment, and incressed by 79.7% compared with the conventional 7075 aluminum alloy under T6 state treatment.(3) After brought Er and Ti into 7075 aluminum alloy, the grain was conspicuously refined. The fatigue crack initiation life of 7075 aluminum alloy containing Er and Ti under T6 state treatment was 33937, reduced by 65% compared with the conventional 7075 aluminum alloy, Intensity ratio(Rsb) of the alloy was 0.99,reduced by 19.5%, compared with the conventional 7075 aluminum alloy, and the tensile strength of the alloy was 579 MPa, increased by 5.6%, the elongation was7.5%, increased by 17.7%, and the hardness was 183.5HV, increased by 1.04%compared with the conventional 7075 aluminum alloy under the T6 state treatment.After a best RRA treatment of 7075 aluminum alloy containing Er and Ti as120℃/16h+190℃/5min +120℃/16 h, the hardness increased to 191.3HV, increased by 4.25% compared with the alloy under the T6 state treatment, and increased by5.3% compared with the conventional 7075 aluminum alloy under the T6 state treatment. After a high temperature retrogression, we got the best aging process as120℃/24h+200℃/10min+120℃/24 h, the tensile strength of the alloy was 572 MPa,the elongation was 8.3%. The tensile strength reduced by 1.4%, and the elongation increased by 9.6%, compared with the 7075 aluminum alloy containing Er and Ti under T6 state treatment. The tensile strength increased by 4.2%, and the elongation increased by 28.9%, compared with the conventional 7075 aluminum alloy under the T6 state treatmen.(4) From the above experiments, the following conclusion could be drawn. The grain could be refined by putting Er and Ti into the 7075 aluminum alloy or by improving the content of Zn in the 7075 aluminum alloy. After brought a high and short temperature retrogression between the two-step aging treatment, the elongation could be improved with the sufficient tensile strength, and the fracture toughness of the 7075 aluminum alloy might be improved. |
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