本文關鍵詞：AZ31鎂合金激光沖擊強化組織及性能研究　出處：《江蘇大學》2017年碩士論文　論文類型：學位論文

  更多相關文章： AZ31鎂合金 LSP 殘余應力 微觀組織 力學性能 疲勞壽命

【摘要】：鎂合金因其質輕高強、良好的鑄造性能及易回收等優(yōu)點而被廣泛應用于汽、航空航天、3C產(chǎn)品等領域。但鎂合金絕對強度低、室溫塑性差、易疲勞等缺點,也使其應用范圍具有很大的局限性。因此,采用激光沖擊強化(LSP)技術來提升鎂合金的強度及疲勞性能具有重要的現(xiàn)實意義。本文以AZ31鎂合金為研究對象,對其進行區(qū)域LSP處理及室溫和熱拉伸實驗、拉-拉疲勞實驗,主要研究工作及結果如下:采用不同功率密度的激光束對鎂合金進行了區(qū)域LSP處理實驗,研究了不同功率密度激光沖擊后材料表層殘余應力分布、顯微硬度和微觀組織的變化情況。結果表明,區(qū)域激光沖擊后鎂合金試樣表層產(chǎn)生了較高幅值的殘余壓應力;表層顯微硬度值提高,且強化層深度隨著激光功率密度的增加而增大;塑變層內(nèi)晶粒得到細化,出現(xiàn)大量的位錯纏結和孿晶及納米晶結構。對AZ31鎂合金進行了室溫及熱拉伸實驗,得到了不同功率密度激光沖擊前后鎂合金的應力-應變曲線,對原始及激光沖擊試樣拉伸斷口形貌進行了分析。結果表明,LSP處理提高了鎂合金室溫及200℃的抗拉強度,并具有一定的熱穩(wěn)定性,延伸率略有降低;激光沖擊試樣斷口表現(xiàn)出少量韌窩和河流花樣組成的準解理斷裂的特征,且在拉-壓應力的弱界面出現(xiàn)層裂紋,200℃變形時,由于動態(tài)再結晶的作用,韌窩深度有所加深。并從殘余應力、晶粒細化及顯微結構這三個方面分析討論了其對鎂合金試樣抗拉強度的影響機理。對AZ31鎂合金帶中心孔試樣進行了拉-拉疲勞實驗,得到了LSP處理前后試樣疲勞壽命,對原始及LSP試樣的疲勞斷口進行了表征與分析。結果表明,LSP處理能顯著改善鎂合金的疲勞性能,且隨激光功率密度的增大疲勞壽命增益越多;LSP使得疲勞裂紋萌生區(qū)從試樣的表面移至次表層,雙面沖擊后疲勞裂紋萌生呈現(xiàn)多源化趨勢,裂紋擴展路徑變得曲折,擴展速率得到降低。此外,還從殘余應力分布、表面狀態(tài)等方面分析討論了其對鎂合金試樣疲勞壽命的影響機理。
[Abstract]:Magnesium alloys are widely used in steam, aerospace and 3C products due to their high strength, good casting properties and easy recovery. However, magnesium alloys have the disadvantages of low absolute strength, poor plasticity at room temperature, easy fatigue and so on. Also makes its application scope has the very big limitation. Laser shock hardening (LSP) technology to improve the strength and fatigue properties of magnesium alloys has important practical significance. This paper takes AZ31 magnesium alloy as the research object. The regional LSP treatment, room temperature and thermal tensile test, tensile fatigue test, the main research work and results are as follows: using laser beam of different power density to carry out regional LSP treatment experiment of magnesium alloy. The changes of residual stress distribution, microhardness and microstructure of the surface layer after laser shock with different power density were studied. The residual compressive stress of the surface layer of magnesium alloy samples after regional laser impact is higher than that of the surface layer. The microhardness of the surface layer increases, and the depth of the strengthened layer increases with the increase of laser power density. The grains in the plastic deformation layer were refined and a large number of dislocation entanglement twins and nanocrystalline structures appeared. The room temperature and hot tensile tests of AZ31 magnesium alloy were carried out. The stress-strain curves of magnesium alloy before and after laser shock with different power density were obtained. The tensile fracture morphology of the original and laser impact samples was analyzed. LSP treatment improved the tensile strength of magnesium alloy at room temperature and 200 鈩，

本文編號：1430004