預時效工藝對7020鋁合金顯微組織和應力腐蝕性能的影響

預時效工藝對7020鋁合金顯微組織和應力腐蝕性能的影響Effect of pre-aging on microstructure and stress corrosion resistance of 7020 aluminum alloy

7020鋁合金經(jīng)470 ℃固溶1 h后分別進行自然時效0 h、168 h以及65 ℃預時效72 h、168 h，再進行(90 ℃，8 h)+(160 ℃，14 h)雙級時效。采用室溫拉伸、慢應變速率拉伸(SSRT)、掃描電鏡(SEM)、透射電鏡(TEM)研究預時效工藝對7020鋁合金的常溫拉伸性能、抗應力腐蝕性能與顯微組織的影響。結果表明:經(jīng)65 ℃、168 h預時效處理后，合金具有最高的抗拉強度Rm=397.4 MPa和最好的抗應力腐蝕性能ISSRT=-0.003; 65 ℃、72 h預時處理效和自然時效168 h后合金的抗拉強度和抗應力腐蝕性能相當，Rm、ISSRT分別為387.6 MPa、0.034和392.0 MPa、0.036;而直接雙級時效合金的抗拉強度和抗應力腐蝕性能最差，Rm、ISSRT為368.9 MPa、0.038。晶內(nèi)析出相η′(MgZn2)的尺寸隨預時效時間的延長而減小，晶界析出相η(MgZn2)的斷續(xù)分布程度隨預時效時間延長而增大。

After solution heat treatment at 470℃ for 1h, the alloys were natural aged for 0 h or 168 h and pre-aged at 65 ℃ for 72 h or 168 h, respectively. And then, the two-step aging ((90 ℃, 8 h)+(160 ℃, 14 h)) was conducted on these alloys. The effect of pre-ageing treatment on the tensile properties, resistances to stress corrosion and microstructures of 7020 aluminum alloy was investigated by tensile test, slow strain rate tensile (SSRT) test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 7020 aluminum alloy aged at 65 ℃ for 168 h pre-ageing treatment has the highest tensile property Rm of 397.4 MPa as well as the best stress corrosion resistance ISSRT of -0.003. The tensile property and stress corrosion resistance of alloy pre-ageing treatment at 65 ℃ for 72 h are 387.6 MPa and 0.034. And it is comparable of that of natural aging 168h, with Rm of 392.0 MPa and ISSRT of 0.036. While the tensile property and stress corrosion resistance of alloy by direct two-step aging are the worst, with Rm of 368.9 MPa and ISSRT of 0.038. With the increase of the pre-aging time, the size of intragranular precipitates η′(MgZn2) inside grains decreases, the intermittent distribution degree of precipitates intragranular precipitates η′(MgZn2) inside grains decreases and the intermittent distribution degree of precipitates η(MgZn2) at the grain boundaries increases.

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