時效工藝對Al-Zn-Mg-Cu合金組織和力學性能的影響

時效工藝對Al-Zn-Mg-Cu合金組織和力學性能的影響Effect of aging process on microstructure and mechanical properties of 7050 aluminum alloy for rail transportation

采用硬度測試、拉伸性能測試、透射電鏡分析(TEM)、掃描電鏡(SEM)斷口形貌觀察以及疲勞性能測試等研究3種時效工藝對軌道交通用Al-Zn-Mg-Cu合金組織和性能的影響。結果表明：三級時效(120 ℃, 0.5 h, WC)+(65 ℃, 240 h)+(120 ℃, 24 h)態(tài)合金的抗拉強度達到640.2 MPa，高于二級時效(120 ℃, 4 h)+(175 ℃, 6 h)態(tài)合金的477.7 MPa和四級時效(105 ℃, 7 h)+(120 ℃, 7 h)+(155 ℃, 4 h)+(175 ℃, 4 h)態(tài)合金的483.5 MPa；二級時效和四級時效態(tài)合金中微米量級第二相粒子數量多，且尺寸較大；而三級時效態(tài)合金中，無論是微米量級第二相還是晶內η′析出相，其尺寸都小于二級和四級時效態(tài)合金的；3種時效工藝疲勞試驗試樣的裂紋源均起于試樣表層，在頻率50 Hz、應力比為-1的加載條件下，二級時效、三級時效和四級時效態(tài)合金的疲勞極限分別約為 145、239和180 MPa。

The effects of aging system on microstructure and mechanical properties of Al-Zn-Mg-Cu alloy for rail transportation were investigated by hardness measurement, tensile test, transmission electron microscopy, scanning electron microscopy observation and fatigue performance tests. The results show that after the three-stage aging (120 ℃, 0.5 h, WC)+(65 ℃, 240 h)+(120 ℃, 24 h) treatment, the tensile strength of alloy is 640.2 MPa, which is higher than 477.7 MPa of the two-stage aging (120 ℃, 4 h)+(175 ℃, 6 h) and 483.5 MPa of the four-stage aging (105 ℃, 7 h)+(120 ℃, 7 h)+(155 ℃, 4 h)+(175 ℃, 4 h). The two-stage aging and four-stage aging samples have the larger number of second phase particles and larger size. However, for the three-stage aging samples, whether it is the micron scale second phase, or intragranular η′ precipitates, their sizes are less than those of the two-stage and four-stage aging samples. The crack sources of three kinds of samples in the aging process fatigue test all start on the sample surfaces. The fatigue limits of the two-stage aging, three-stage aging and four-stage aging alloys are about 145 MPa, 239 MPa and 180 MPa, respectively.

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