AZ31镁合金激光冲击强化组织及性能研究

发布时间：2018-01-15 20:42

  本文关键词：AZ31镁合金激光冲击强化组织及性能研究　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

  更多相关文章： AZ31镁合金 LSP 残余应力 微观组织 力学性能 疲劳寿命

【摘要】：镁合金因其质轻高强、良好的铸造性能及易回收等优点而被广泛应用于汽、航空航天、3C产品等领域。但镁合金绝对强度低、室温塑性差、易疲劳等缺点,也使其应用范围具有很大的局限性。因此,采用激光冲击强化(LSP)技术来提升镁合金的强度及疲劳性能具有重要的现实意义。本文以AZ31镁合金为研究对象,对其进行区域LSP处理及室温和热拉伸实验、拉-拉疲劳实验,主要研究工作及结果如下:采用不同功率密度的激光束对镁合金进行了区域LSP处理实验,研究了不同功率密度激光冲击后材料表层残余应力分布、显微硬度和微观组织的变化情况。结果表明,区域激光冲击后镁合金试样表层产生了较高幅值的残余压应力;表层显微硬度值提高,且强化层深度随着激光功率密度的增加而增大;塑变层内晶粒得到细化,出现大量的位错缠结和孪晶及纳米晶结构。对AZ31镁合金进行了室温及热拉伸实验,得到了不同功率密度激光冲击前后镁合金的应力-应变曲线,对原始及激光冲击试样拉伸断口形貌进行了分析。结果表明,LSP处理提高了镁合金室温及200℃的抗拉强度,并具有一定的热稳定性,延伸率略有降低;激光冲击试样断口表现出少量韧窝和河流花样组成的准解理断裂的特征,且在拉-压应力的弱界面出现层裂纹,200℃变形时,由于动态再结晶的作用,韧窝深度有所加深。并从残余应力、晶粒细化及显微结构这三个方面分析讨论了其对镁合金试样抗拉强度的影响机理。对AZ31镁合金带中心孔试样进行了拉-拉疲劳实验,得到了LSP处理前后试样疲劳寿命,对原始及LSP试样的疲劳断口进行了表征与分析。结果表明,LSP处理能显著改善镁合金的疲劳性能,且随激光功率密度的增大疲劳寿命增益越多;LSP使得疲劳裂纹萌生区从试样的表面移至次表层,双面冲击后疲劳裂纹萌生呈现多源化趋势,裂纹扩展路径变得曲折,扩展速率得到降低。此外,还从残余应力分布、表面状态等方面分析讨论了其对镁合金试样疲劳寿命的影响机理。
[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，

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