本文選題：Mg-Zn-Y-Zr合金 + 時效處理�。� 參考：《西南交通大學(xué)》2017年碩士論文

【摘要】：鎂合金作為最輕的金屬材料,普遍應(yīng)用于交通運輸、航天裝備等領(lǐng)域。目前鎂合金受限于其強度而多用于制造非承力部位的零件。重要承力零部件容易在長時間交變載荷作用下發(fā)生疲勞斷裂,因此開發(fā)一款高強度和疲勞性能優(yōu)異的鎂合金成為重要的任務(wù)。本課題選取自行開發(fā)的稀土鎂合金Mg-2.3Zn-0.18Y,通過加入不同含量的Zr(0.03,0.06,0.13 at.%)元素以及熱擠壓變形方式得到性能優(yōu)異的Mg-2.3Zn-0.18Y-xZr鎂合金。首先,研究擠壓態(tài)Mg-2.3Zn-0.18Y-xZr鎂合金高周疲勞性能和裂紋萌生、擴展機理;其次,選取高周疲勞性能較優(yōu)的Mg-2.3Zn-0.18Y-0.13Zr合金作為研究對象,分別通過時效處理和噴丸處理提高其高周疲勞性能;最后,分別闡述各工藝下的裂紋萌生、擴展機理和強化機理。得到主要結(jié)論如下:(1)隨著 Zr 含量的增加,Mg-2.3Zn-0.18Y-xZr(x=0.03、0.06、0.13 at.%)合金的α-Mg平均晶粒尺寸從9.9μm減少到4.8μm;抗拉強度、屈服強度和延伸率都有所提高,其中Mg-2.3Zn-0.18Y-0.13Zr合金的力學(xué)性能最好,分別達到346MPa、292MPa和26.7%,其疲勞強度為150MPa。另外,Mg-2.3Zn-0.18Y-0.03Zr合金疲勞斷口顯微組織的粗大晶粒中發(fā)現(xiàn)有孿晶生成,說明孿生變形影響此合金的塑性變形方式。(2)當(dāng)應(yīng)力水平較高(180MPa)時,擠壓Mg-2.3Zn-0.18Y-xZr合金的高周疲勞裂紋源只有一個。當(dāng)應(yīng)力水平較低(160MPa)時,疲勞裂紋源有多個。裂紋萌生于試樣表面或表面的第二相顆粒處且沿著解理面進行擴展,呈穿晶斷裂模式。(3)Mg-2.3Zn-0.18Y-0.13Zr合金的較佳時效處理工藝參數(shù)為180℃、12h。經(jīng)過此時效工藝參數(shù)處理的Mg-2.3Zn-0.18Y-0.13Zr合金的綜合力學(xué)性能較優(yōu),其抗拉強度、屈服強度和延伸率分別達到353±4MPa、323±4MPa和20.3%±2.0%。(4)欠時效態(tài)Mg-2.3Zn-0.18Y-0.13Zr合金的疲勞強度為160MPa,比擠壓態(tài)合金的疲勞強度高6.7%。這是因為時效處理當(dāng)中析出的MgZn2相顆粒抑制基面上的位錯滑移,提高裂紋萌生的最大應(yīng)力,從而提高合金的疲勞壽命。(5)Mg-2.3Zn-0.18Y-0.13Zr合金較佳噴丸處理的氣壓強度為0.4MPa,且對噴丸處理的敏感性較大,優(yōu)化區(qū)間較窄。(6)經(jīng)較佳噴丸工藝處理后的Mg-2.3Zn-0.18Y-0.13Zr合金疲勞強度為173MPa,較擠壓態(tài)合金的疲勞強度提高了 23MPa,提升幅度為15%。試樣經(jīng)噴丸處理后,裂紋源從試樣的表面處轉(zhuǎn)移到試樣的亞表面處,變形層組織明顯得到細(xì)化。裂紋的萌生時間增長,從而延長合金的疲勞壽命。
[Abstract]:As the lightest metal material, magnesium alloy is widely used in transportation, aerospace equipment and other fields. At present, magnesium alloy is limited by its strength and is used to manufacture parts in non-bearing parts. The fatigue fracture of important load-bearing parts is easy to occur under the action of long time alternating load, so it is an important task to develop a magnesium alloy with high strength and excellent fatigue properties. In this paper, Mg-2.3Zn-0.18Y magnesium alloy with excellent properties was obtained by adding different contents of Zr0.03Zn-0.13at.and hot extrusion deformation method. The Mg-2.3Zn-0.18Y-xZr magnesium alloy with excellent properties was obtained by adding different contents of Zr0.03Zn-0.13at.and hot extruding deformation mode of Mg-2.3Zn-0.18Y-xZr magnesium alloy. Firstly, the high cycle fatigue properties and crack initiation and propagation mechanism of extruded Mg-2.3Zn-0.18Y-xZr magnesium alloy were studied. Secondly, Mg-2.3Zn-0.18Y-0.13Zr alloy with high cycle fatigue property was selected as the research object, and the high cycle fatigue property was improved by aging treatment and shot peening respectively. Finally, the crack initiation, propagation mechanism and strengthening mechanism are described respectively. The main conclusions are as follows: (1) with the increase of Zr content, the average grain size of 偽 -Mg decreases from 9.9 渭 m to 4.8 渭 m, and the tensile strength, yield strength and elongation of Mg-2.3Zn-0.18Y-0.13Zr alloy are improved, and the mechanical properties of Mg-2.3Zn-0.18Y-0.13Zr alloy are the best, and the average grain size of the alloy decreases from 9.9 渭 m to 4.8 渭 m, and the mechanical properties of Mg-2.3Zn-0.18Y-0.13Zr alloy are better than that of Mg-2.3Zn-0.18Y-0.13Zr alloy. The fatigue strength is 150 MPA and the fatigue strength is 346 MPA and 26.7 MPA, respectively. In addition, twin formation was found in the coarse grains of fatigue fracture microstructure of Mg-2.3Zn-0.18Y-0.03Zr alloy, indicating that twinning deformation affects the plastic deformation mode of the alloy. When the stress level is high (180MPa), the high cycle fatigue crack source of extruded Mg-2.3Zn-0.18Y-xZr alloy is only one. When the stress level is low (160 MPA), there are many fatigue crack sources. The crack originates at the second phase particle on the surface or surface of the specimen and propagates along the cleavage surface. The best aging process parameter of the alloy is 180 鈩，

本文編號：2048967