【作者】 王丽；

【导师】 熊建钢；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2007， 硕士

【摘要】 块体非晶合金因其独特的结构而具有晶态合金所无法比拟的优异性能,如高的强度、硬度、耐磨性、耐蚀性和良好的软磁特性,在机械、电子、化工、航空航天等工程领域具有广阔的应用前景。块体非晶的连接是其工程应用的一个重要方面,因此,研究块体非晶合金在焊接过程的晶化机理具有非常重要的现实意义。本文在前人研究的基础上,对块体非晶合金Zr₄₅Cu₄₈Al₇的激光焊接性能进行研究,讨论了在小功率300～500W、焊接速度3～4m/min条件下激光焊接块体非晶合金Zr₄₅Cu₄₈Al₇的特点。焊接结果表明:所有试样焊缝和热影响区的过渡区出现了不同程度的晶化;在激光焊接功率为500W,焊接速度3.0 m/min,过渡区主要是粗大枝状晶,随着焊接速度的升高,达到4.0 m/min,过渡区的枝状晶组织变得短小,出现中心晶粒。在功率为500W,焊接速度从3.0 m/min上升到4.0 m/min的过程中,焊缝和热影响区的晶化程度均降低,在焊接速度为4.0 m/min的试样焊缝中没有看到晶粒,则可能保持了非晶态;从每个薄片的焊缝和热影响晶化程度来看,热影响区要比焊缝更容易发生晶化。在激光焊接功率为300W,焊接速度为4.0m/min,焊缝和热影响区均没有看到晶粒,则可能保持了非晶态,而过渡区则出现了呈弧形分布的稀疏的点状晶粒,发生了部分晶化。运用差热扫描量热法（DSC）和Kissinger法计算块体非晶合金Zr₄₅Cu₄₈Al₇的连续加热和冷却过程晶化激活能,从动力学角度分析了块体非晶合金Zr₄₅Cu₄₈Al₇热影响区内的合金比焊缝更容易发生晶化,这与实验的结果一致。焊缝区域的非晶合金在焊接过程中的非晶态结构的关键因素是如何保证其熔融冷却曲线避免与其等温转变（T-T-T）曲线相交,是液态金属合金的非晶形成能力的问题;热影响区的非晶合金在激光焊接热循环作用下始终保持固态,影响热影响区的非晶合金晶化的主要因素是在冷却降温阶段,这是块体非晶合金热稳定性问题。应用大型有限元分析软件ANSYS,以双椭球为热源模型,对块体非晶合金Zr₄₅Cu₄₈Al₇的激光焊接过程的温度场进行了模拟,得到各部分热循环曲线,在此基础上对激光焊接实验结果进行了验证和深入分析。更多还原

【Abstract】 It is well known that bulk metallic glasses （BMGs） possess many excellent properties such as high strength, high stiffness, improved abrasion resistance, high corrosion resistances and good soft-magnetic properties compared with crystalline alloys. So the BMGs have a wide application prospect in mechanical industry, electronic industry, chemical industry and avigation industry. The joining of the BMGs is an important aspect in engineering application of BMGs. Therefore, the investigation of the crystallization mechanics under the action of the thermal cycle makes a good sense nowadays.In this dissertation, the laser beam welding technology continued to be used to joint the BMGs Zr₄₅Cu₄₈Al₇ under the low output power among 300～500W and the scanning velocity among 3～4m/min after some tries in high output power by some pioneers. The result showed crystallization occurred in the melt zones of all samples; and the main crystallization phase was like crassitude branches in the output of 500W and the scanning velocity of 3m/min, when the scanning velocity got to the 4m/min, which became shorter and the center crystallization phase turned up. The alloys in the bead and head-affected zone might keep amorphous when output power is 300W or 500W, and the scanning velocity is 4m/min, but crystallization occurred in the melt zone. The activation energy of BMGs had been calculated by the method of DSC and Kissinger in the continued heated and cooled processing, and that result suggested that head-affected zone was easier to crystal than the bead which agreed with the result of experiments. The key of alloys in bead which kept amorphous in the process of laser beam welding was that how to avoid the intersect of the melted -cooled cycle and T-T-T cycle, and that is related the formation ability of the liquid BMGs. The head-affected zone always kept solid in the process of laser beam welding and the main factor which deeply affected the zone lied in the cooled process, which was about the thermal stability of solid BMGs. The laser beam welding process were simulated using commercial Finite Element Method （FEM） program ANSYS. And the model of heated resource was double ellipse spheres. The dynamic temperature field and the heat cycle of the BMGs Zr₄₅Cu₄₈Al₇ had been obtained, on the base of which the result of the weld experiment is detailed analyzed.更多还原