【作者】 宋刚；

【导师】 刘黎明；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2006， 博士

【摘要】 镁合金具有密度低、比强度和比刚度高、电磁屏蔽和抗辐射性能好以及易回收等一系列优点，被称为二十一世纪的绿色工程材料，在航天航空、汽车、电子等领域具有巨大的应用潜力。我国作为镁资源大国，镁合金的产业化应用已成为国家科技战略发展目标之一。在镁合金的产业化应用过程中，连接技术始终是关键。因此开发优质、高效、节能、降耗的镁合金先进连接技术已成为国内外研究的热点。镁合金低功率激光-电弧复合热源焊接技术的研究便是在这种背景下产生的。 1．提出镁合金低功率激光-氩弧复合热源焊接工艺，采用500W掺钕钇铝石榴石（Nd：YAG）固体脉冲激光器与钨极交流电弧（以下简称TIG）相复合，建立复合热源焊接系统。以AZ31B、AZ61、AZ91D镁合金为主要研究对象，进行镁合金低功率复合热源焊接工艺研究，系统分析焊接参数对镁合金焊缝成形以及激光与电弧复合增强效果的影响。试验结果表明，采用低功率激光-氩弧复合热源焊接技术能够实现AZ31B、AZ61、AZ91D镁合金良好连接，焊接接头表面成形连续致密，没有飞溅、裂纹、气孔等表面缺陷。在优化的工艺条件下，低功率激光-电弧复合热源焊接接头熔深可达TIG焊接接头熔深的2倍，激光单独焊接的4倍以上；焊接速度可达TIG焊接速度的3～5倍，能够实现镁合金的高效、低成本连接。通过分析激光与电弧相互作用形态发现，在低功率复合热源焊接过程中，激光脉冲与焊接电弧之间存在三种作用方式，即激光脉冲分别作用于交流电弧正半波、负半波及交流电弧过零点处。根据此现象提出镁合金低功率激光与交流电弧相互作用模型。根据工艺试验结果以及激光与电弧相互作用特点，首次提出镁合金低功率激光诱导交流电弧负半波放电理论。 2．利用现代化分析检测手段分析同种和异种镁合金复合热源焊接接头的微观组织和力学性能。镁合金焊接接头微观组织观察发现，由于复合热源焊接工艺具有焊接速度快，热输入小等特点，镁合金具有高的热传导率，因此镁合金复合焊接接头呈典型的铸态激冷组织，焊缝由细小等轴晶组成。AZ31B焊接接头无明显的热影响区存在，而AZ61、AZ91D焊接接头发现存在较宽热影响区。这是因为在Al含量较高的镁合金焊接接头中存在大量低熔点的β(Mg（17）Al₁₂)相，根据β(Mg₁₇Al₁₂)相析出的数量和形态，本文将AZ91D镁合金焊接接头热影响区分为三部分，即晶界浮凸区（Ⅰ）、粒状β相析出区（Ⅱ）、带状β相形成区（Ⅲ）。镁合金复合焊接接头具有优良的综合力学性能，以AZ31B为例，镁合金AZ31B复合焊接接头的拉伸强度可达到母材的95％～100％，疲劳强度与母材的疲劳强度相当。AZ31B与AZ61和AZ91D异种镁合金复合热源焊接接头的微观组织均匀，由细小等轴晶粒组成，焊接接头的拉伸强度略高于AZ31B镁合金母材。更多还原

【Abstract】 For the characteristics of low density, high specific strength, good electromagnetic shielding, anti-radiation and recycleable, Mg alloys are praised of the green engineering material in 21st century, which have recently attracted great attention in academic research and industry application. Applications in aerospace vehicle, automobile, consumer electronic productions have been widely and rapidly extended. As a country with abundant Mg resource, the industrialization of Mg has been become the one of tactic aims of science and technology in our country. However, the single welding technique of Mg and its alloy can’t meet the demands of manufacturing at present and it has been the main problem which limits the application of magnesium alloy structural components. Hereby, the research on Mg welding technology is becoming a focal topic all over the world in order to acquire the advanced joining technique with advantages of high quality, high efficiency and energy saving. So the research on hybrid welding technology comes into being.1. Low-power laser-TIG hybrid welding process combining with 500W YAG pulsed laser and a tungsten inert gas welding arc is put forward for Mg welding alloy firstly in this dissertation. Taking AZ31B, AZ61 and AZ91D commercial alloys as subjects investigated, the low-power laser-TIG hybrid welding behaviors of the AZ-based Mg alloys in similar and dissimilar are investigated, in terms of welding parameters, fusion-zone characteristics, mechanical properties, welding temperature fields and the behavior of arc plasma and laser-induced plume. The results of experiments indicate clearly that AZ31B AZ61 and AZ91D magnesium alloys can be welded easily by low-power laser-TIG hybrid welding process. The top surface of weld is smooth and continuous without defects such as spattering, crack and undercutting in high speed welding. Comparing the penetrations of laser TIG and hybrid welding, it is found that the penetration of hybrid welding is 2 times of TIG welding, and 4 times of laser welding. The speed of hybrid welding can achieve 3-5 times of TIG alone. The high speed image system of arc behaviors in hybrid welding of magnesium is set up, by which the photographs of arc behavior that laser and arc act on each other are obtained. It is found that there are three ways that laser and arc act on each other, according to which the model of that is found. Based on the experiment results and hybrid mechanism that laser and arc act on each other, three kinds of mechanisms that the penetration of laser-TIG hybrid更多还原