【摘要】：鎂合金具有密度低、強度高、良好的阻尼性和減震性能,而且它的熱容量低、凝固速度快、鑄造成型性能好。鎂合金的循環(huán)利用性好,回收再利用率高,回收熔化時所消耗的能量較少,并且使用回收的鎂合金制作構(gòu)件時不會降低其力學性能。被譽為“21世紀最具發(fā)展的綠色工程材料”。ZK60鎂合金作為目前商用變形鎂合金中強度最高者,提高構(gòu)件的塑性,對擴大鎂合金的應用至關(guān)重要。但是商業(yè)鎂合金板材總會存在一定的缺陷,進而影響性能,使用熱處理的方法可以有效地減少缺陷。因此,論文通過研究熱處理條件下ZK60鎂合金微觀組織的變化,探討其對疲勞斷裂行為的影響,這對進一步推動ZK60鎂合金在實際生產(chǎn)生活中的應用具有一定的意義。論文采用萬能試驗機對ZK60鎂合金板材以及熱處理后試樣的拉伸性能進行分析,利用疲勞試驗機分析鎂合金的疲勞裂紋擴展特征。利用SEM、XRD等測試手段對熱處理后鎂合金進行物相分析。ZK60鎂合金板材晶粒尺寸26μm,固溶處理以后的試件晶粒平均尺寸大約是31μm。之后進行時效熱處理從5h~20h時,晶粒尺寸先減少后變得粗大。時效10h時,晶粒的尺寸最小。ZK60鎂合金板材和固溶處理以后的拉伸強度分別是294MPa和301MPa。時效處理后試樣的強度為325MPa,相對ZK60鎂合金板材來說有較大的提高,延伸率以及屈服強度都有所提高,通過XRD分析可知,ZK60鎂合金板材主要有由α-Mg,MgZn,MgZn2相組成,固溶處理之后試樣中的MgZn相全部融入基體中,Mg Zn2大量溶入到基體中只有少量殘余,但是時效處理后有MgZn和MgZn2重新析出。試樣受到循環(huán)載荷次數(shù)為107時,ZK60鎂合金板材的疲勞強度為91.62MPa,試件在經(jīng)過固溶處理(T4)及固溶時效處理(T6)之后疲勞強度分別為102.46MPa和117.76MPa,經(jīng)過時效處理之后試件的疲勞強度相對于ZK60鎂合金板材提高28.31%。ZK60鎂合金板材的疲勞斷口為脆性斷裂斷口,而熱處理之后在裂紋萌生區(qū)發(fā)現(xiàn)許多凹坑,裂紋擴展區(qū)域存在準解理斷裂特征。裂紋擴展速率試驗表明,時效5h的試件裂紋的擴展速率稍慢于固溶處理的試件。ZK60鎂合金時效10h,抵御裂紋擴展能力得到提高。時效15h時,裂紋擴展速率沒有繼續(xù)下降,反而有所提高。當時效20h時裂紋擴展速率加快。所以固溶處理之后,時效10h時,ZK60鎂合金的抵抗裂紋擴展的性能最優(yōu)。通過分析裂紋擴展速率的斷口,在裂紋開始擴展階段,固溶處理的試樣斷口含有小坑,屬于脆性斷裂斷口,時效處理的斷口相對平滑。在時效處理試件的穩(wěn)定擴展區(qū)可以發(fā)現(xiàn)二次裂紋。在時效處理的瞬斷區(qū)內(nèi)有許多韌窩,它可以提高抵御裂紋擴展的能力。通過塑性半徑公式計算出ZK60鎂合金板材,固溶處理的試樣和時效處理后的試樣裂紋尖端的塑性半徑分別為10.5μm和10.1μm,平均晶粒尺寸大于塑性半徑,發(fā)現(xiàn)時效處理的ZK60鎂合金相對于固溶處理的ZK60鎂合金具有更小的塑性半徑,即有更小的塑性區(qū),所以使得試件抵御裂紋擴展能力加強。
[Abstract]:Magnesium alloys have the advantages of low density, high strength, good damping and damping properties, low heat capacity, fast solidification speed and good casting formability. ZK60 magnesium alloy is regarded as the most developed green engineering material in the 21st century. As the highest strength of commercial wrought magnesium alloy, improving the plasticity of components is very important for expanding the application of magnesium alloy. Therefore, this paper studies the microstructure changes of ZK60 magnesium alloy under heat treatment, and discusses its influence on fatigue fracture behavior, which has certain significance for further promoting the application of ZK60 magnesium alloy in practical production and life. The tensile properties of ZK60 magnesium alloy were analyzed by fatigue testing machine and the fatigue crack propagation characteristics were analyzed by SEM and XRD. The grain size of ZK60 magnesium alloy sheet was 26 micron. The average grain size of ZK60 magnesium alloy after solution treatment was about 31 micron. The tensile strength of ZK60 magnesium alloy sheet is 294 MPa and 301 MPa respectively after solution treatment. The strength of the sample after aging treatment is 325 MPa, which is higher than that of ZK60 magnesium alloy sheet. The elongation and yield strength are both improved by XRD analysis. It is known that ZK60 magnesium alloy sheet is mainly composed of a-Mg, MgZn and MgZn2 phases. After solution treatment, all MgZn phases in the sample are incorporated into the matrix, while Mg-Zn2 is dissolved into the matrix with a small amount of residual, but MgZn and MgZn2 are re-precipitated after aging treatment. The fatigue strength of ZK60 magnesium alloy sheet is 9 when the number of cyclic loading is 107. The fatigue strength of the specimens after solution treatment (T4) and solution aging treatment (T6) were 102.46 MPa and 117.76 MPa, respectively. The fatigue strength of the specimens after aging treatment was 28.31% higher than that of ZK60 magnesium alloy sheet. The fatigue fracture of ZK60 magnesium alloy sheet was brittle fracture, and the crack initiation zone was found after heat treatment. The crack growth rate test showed that the crack growth rate of the specimens aged for 5 h was slightly slower than that of the specimens treated by solid solution. The crack growth rate of ZK60 magnesium alloy increases at h, so the crack growth resistance of ZK60 magnesium alloy is the best after solution treatment and aging for 10 h. By analyzing the fracture surface of crack growth rate, at the beginning of crack growth stage, the fracture surface of the sample treated by solution treatment contains pits, which belongs to brittle fracture surface, and the fracture surface of aging treatment is relatively smooth. Secondary cracks can be found in the stable propagation zone of the specimens.There are many dimples in the transient fracture zone after aging treatment,which can improve the resistance to crack propagation.The plastic radius of ZK60 magnesium alloy sheet is calculated by the plastic radius formula.The plastic radius of the crack tip of the solution treated specimens and the aging treated specimens are 10.5 and 10.1 microns,respectively. The grain size is larger than the plastic radius. It is found that the aging treatment ZK60 magnesium alloy has a smaller plastic radius than the solution treatment ZK60 magnesium alloy, that is, there is a smaller plastic zone, which makes the specimen more resistant to crack propagation.
【學位授予單位】：太原理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG146.22;TG166.4

【參考文獻】

相關(guān)期刊論文 前10條

1 付杰;董炎鋒;付廣柱;;熱處理對提高疲勞強度與修復疲勞裂紋的影響[J];熱處理技術(shù)與裝備;2014年06期

2 閆志峰;張紅霞;王文先;王凱;裴飛飛;;紅外熱像法預測鎂合金的疲勞性能[J];機械工程材料;2012年02期

3 何振波;彭勇宜;尹志民;雷學鋒;;Al-Mg-Mn-Sc-Zr合金板材攪拌摩擦焊和氬弧焊焊接接頭的對比(英文)[J];Transactions of Nonferrous Metals Society of China;2011年08期

4 何柏林;;超聲沖擊對鎂合金焊接接頭疲勞性能的研究現(xiàn)狀[J];華東交通大學學報;2011年03期

5 張建民;馬澤飛;張寶紅;;T6熱處理對變形AZ91D鎂合金的強化作用[J];熱加工工藝;2010年16期

6 蔣永鋒;包曄峰;郁中太;;不同退火條件下AZ31鎂合金的組織和硬度分析[J];熱加工工藝;2009年04期

7 劉政軍;成明華;田雨;趙倩;張世鑫;蘇允海;;外加磁場對鎂合金焊接接頭疲勞性能的影響[J];熱加工工藝;2009年03期

8 王建強;丁占來;關(guān)紹康;侯哲哲;;人工時效對RE變質(zhì)ZA84鎂合金力學性能與阻尼性能的影響[J];熱加工工藝;2006年02期

9 王志虎;張菊梅;袁森;蔣百靈;;鎂合金強韌化處理研究進展[J];鑄造技術(shù);2006年01期

10 馮吉才,王亞榮,張忠典;鎂合金焊接技術(shù)的研究現(xiàn)狀及應用[J];中國有色金屬學報;2005年02期

相關(guān)博士學位論文 前3條

1 張紅霞;AZ31B鎂合金及其TIG焊焊接接頭疲勞斷裂行為及評定研究[D];太原理工大學;2010年

2 常麗麗;變形鎂合金AZ31的織構(gòu)演變與力學性能[D];大連理工大學;2009年

3 郭強;鎂合金高溫單向壓縮及多向變形行為研究[D];湖南大學;2007年

相關(guān)碩士學位論文 前2條

1 樊世波;Ce元素對ZM21鎂合金組織和性能的影響[D];重慶大學;2010年

2 蘇燕鈴;孿生在鎂合金塑性變形中的作用[D];南京理工大學;2007年

，

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