先进材料连接技术(1)-材料连接技术概况

1、第一章第一章材料连接技术的发展状况材料连接技术的发展状况2Categories of Joining Technologies Mechanical Joining Adhesive Bonding Welding 45%3连接技术的分类（1） 机械连接 胶接 焊接 45%4连接技术的分类（连接技术的分类（2） 机械连接机械连接 铆接铆接-使用铆钉连接两件或两件以上的工件叫铆接。使用铆钉连接两件或两件以上的工件叫铆接。 螺栓连接。螺栓连接。5连接技术的分类（连接技术的分类（3） 机械连接机械连接 实例照片实例照片6 胶接胶接 胶接技术是借助胶粘剂在固体表面上所产生的粘合胶接技术是借助胶粘剂在固

2、体表面上所产生的粘合力力,将同种或不同种材料牢固地连接在一起的方法。将同种或不同种材料牢固地连接在一起的方法。连接技术的分类（连接技术的分类（4）7 焊接焊接 通过加热或加压或二者并用，使被焊材料达到原子通过加热或加压或二者并用，使被焊材料达到原子间的结合，从而形成永久性连接的工艺。间的结合，从而形成永久性连接的工艺。连接技术的分类（连接技术的分类（5）89Applications of Friction Stir WeldingLeft top: the 2195 Al-Li Space Shuttle external tankLeft bottom: The Eclipse 500 bu

3、siness class jetRight: Mazda RX-8 rear doorFrom Welding Journal 200810Definition of Welding The process of joining together two pieces of metal so that bonding accompanied by appreciable interatomic penetration takes place at their original boundary surfaces. The boundaries more or less disappear at

4、 the weld, and integrating crystals develop across them. Welding is carried out by the use of heat or pressure or both and with or without added metal.11焊接的定义焊接的定义 焊接技术是指将两种或两种以上的（同种或异焊接技术是指将两种或两种以上的（同种或异种）材料通过种）材料通过原子或分子之间的结合和扩散原子或分子之间的结合和扩散造造成成永久性连接永久性连接的工艺过程。的工艺过程。 宏观上：永久性联系宏观上：永久性联系 微观上：组织之间的内部联

5、系微观上：组织之间的内部联系12Advantages and disadvantages of weldingAdvantagesJoints are permanent, precluding accidental (or even intentional) disassembly and looseningWide variety of process embodimentsApplicability to many materials within a fundamental classCan be portableReasonable overall cost, usuallyProv

6、ides leak tightness with continuous weldsDisadvantagesPrevents/precludes disassembly for any purposeHeat of some welding (especially involving fusion) disrupts base material propertiesPrecludes joining between materials from different classesUnbalanced heat input leads to distortion or residual stre

7、ssesRequires considerable operator skillCan be expensive due to skilled labor rates or due to labor intensity for thick, long, or critical weldsCapital equipment can be expensive, especially for some automated processes13Schematic illustration of the various microstructural zones in a typical fusion

8、 weld14Types of jointsWelding joints variationsWelding positions15Classification of Welding Processes Fusion welding gas welding, shielded metal arc welding, gas metal arc welding (aka. MIG), gas tungsten arc welding (aka. TIG), plasma arc welding, submerged arc welding, electroslag welding, electro

9、n beam welding, laser beam welding, etc. Pressure welding resistance welding, friction welding, diffusion welding, flash welding, explosion welding, ultrasonic welding, friction stir welding, etc. Brazing and Soldering 450 oC (840 oF) induction, furnace, dip, torch, resistance, etc.How many more wel

10、ding processes can you name?Arc weldingLaser beam weldingSoldering 16焊接方法的分类焊接方法的分类 熔焊熔焊 气焊、焊条电弧焊、熔化极气体保护焊（气焊、焊条电弧焊、熔化极气体保护焊（MIG）、钨极气）、钨极气体保护焊（体保护焊（TIG）、等离子弧焊、埋弧焊、电子束焊、激）、等离子弧焊、埋弧焊、电子束焊、激光焊、电渣焊等光焊、电渣焊等 压焊压焊 电阻焊、摩擦焊、扩散焊、冷压焊、爆炸焊、超声波焊、电阻焊、摩擦焊、扩散焊、冷压焊、爆炸焊、超声波焊、搅拌摩擦焊等搅拌摩擦焊等 钎焊钎焊 软钎焊、硬钎焊软钎焊、硬钎焊 感应钎焊、炉中钎焊、

11、浸沾钎焊、火焰钎焊、电阻钎焊等感应钎焊、炉中钎焊、浸沾钎焊、火焰钎焊、电阻钎焊等17Gas Welding Gas welding is a welding process that melts and joins metals by heating them with a flame caused by the reaction between a fuel gas and oxygen. Fuel gases: acetylene (乙炔), propane (丙烷), propylene (丙烯), hydrogen (氢气), etc. Oxyacetylene welding (OA

12、W, 氧乙炔焊氧乙炔焊) is the most commonly used gas welding process because of its high flame temperature or source energy.18气焊气焊 气焊是金属熔焊方法的一种，所需要的热源由气气焊是金属熔焊方法的一种，所需要的热源由气体火焰提供。体火焰提供。 所用燃气有乙炔、丙烷、丙烯、氢气等，但乙炔所用燃气有乙炔、丙烷、丙烯、氢气等，但乙炔在气焊中占主导地位。氧在气焊中占主导地位。氧-乙炔气焊最常用乙炔气焊最常用（Oxy-Acetylene Welding ）。）。 气焊的应用范围越来越小。常用于黑色

13、金属焊接。气焊的应用范围越来越小。常用于黑色金属焊接。在建筑、安装、装修及野外施工等没有电源的场在建筑、安装、装修及野外施工等没有电源的场所，无法进行电焊时常使用气焊。所，无法进行电焊时常使用气焊。 与气割的区别。与气割的区别。19Gas Welding20气焊设备气焊设备 氧气瓶氧气瓶 氧气减压器氧气减压器 乙炔瓶乙炔瓶 回火保险器回火保险器 焊炬（枪）焊炬（枪） 橡皮管橡皮管气焊气焊焊炬构造图焊炬构造图21Three types of flames in oxyacetylene welding(a 中性火焰中性火焰, b 碳化火焰碳化火焰, c 氧化火焰氧化火焰)O2:C2H2=1:1O

14、2:C2H21:1for brassfor aluminum,high-carbon steelsfor most metalsGas Welding22Gas WeldingChemical reactions and temperature distribution in a neutral oxyacetylene flame23Advantages The equipment is simple, portable, and inexpensive The temperature in the weld pool is controllable For all-position wel

15、ding Field construction without electrical source Convenient for maintenance and repair applicationsDisadvantages Limited power density, low welding speed, high total heat input per unit length of the weld Large heat-affected zones Severe distortion Mostly operated manually, high requirements of lab

16、or skills Poor working conditionsGas Welding24气焊优点气焊优点 焊接熔池温度易于控制，焊接熔池温度易于控制，可以全位置焊接可以全位置焊接 不需要电源，可在野外施不需要电源，可在野外施工工 设备简单，移动方便设备简单，移动方便 通用性强，可用于熔焊、通用性强，可用于熔焊、钎焊，可改装成气割设备钎焊，可改装成气割设备 适于薄件、小件焊接和熔适于薄件、小件焊接和熔点较低的金属焊接点较低的金属焊接气焊气焊气焊缺点气焊缺点 与电弧相比，气体火焰与电弧相比，气体火焰温度低，热量分散温度低，热量分散 生产率低，焊件变形严生产率低，焊件变形严重，接头热影响区宽，重

17、，接头热影响区宽，显微组织粗大，接头性显微组织粗大，接头性能较差能较差 多为手工操作，对焊工多为手工操作，对焊工有较高的技巧要求有较高的技巧要求 劳动条件差劳动条件差25(1) Area of applicationMost ferrous and non-ferrous metalsOAW: carbon steels, cast iron, alloyed steels, copper, nickel, aluminum, etc.With other fuel gases: low-melting point metals and noble metals, e.g. aluminum,

18、 magnesium, zinc, lead, etc.Not recommended for refractory metals (niobium, molybdenum, wolfram) and reactive metals (titanium, zirconium). (2) Main applicationsThin sheets, thin-section tubesSmall batch production, field construction, repair, etc.Gas Welding26气焊气焊适用范围气焊适用范围（1）可气焊的金属）可气焊的金属绝大多数的黑色和有

19、色金属。绝大多数的黑色和有色金属。用用氧氧-乙炔火焰乙炔火焰时，可焊接碳钢、铸铁、时，可焊接碳钢、铸铁、合金钢、铜合金、镍合金、铝合金等。合金钢、铜合金、镍合金、铝合金等。用用氢、天然气、丙烷氢、天然气、丙烷等其它可燃气体等其它可燃气体时，可焊接熔点较低的金属和贵重金时，可焊接熔点较低的金属和贵重金属，如铝、镁、锌、铅等。属，如铝、镁、锌、铅等。高熔点金属如铌、钼、钨等以及活性高熔点金属如铌、钼、钨等以及活性金属如钛、鋯等不宜采用气焊。金属如钛、鋯等不宜采用气焊。（2）主要用途）主要用途最适于焊接薄板或薄壁管子。随着板最适于焊接薄板或薄壁管子。随着板厚增加，焊接越不经济。由于生产率厚增加，焊接

20、越不经济。由于生产率低，故适用于小批生产、野外焊接、低，故适用于小批生产、野外焊接、修理和改建等场合。修理和改建等场合。27Shielded Metal Arc Welding (SMAW) Shielded metal arc welding (SMAW) is a process that melts and joins metals by heating them with an arc established between a sticklike covered electrode and the metals. It is often called stick welding.Th

21、e core of the covered electrode, the core wire, conducts the electric current to the arc and provides filler metal for the joint. For electrical contact, the top 1.5 cm of the core wire is bare and held by the electrode holder. The electrode holder is essentially a metal clamp with an electrically i

22、nsulated outside shell for the welder to hold safely.28焊条电弧焊（焊条电弧焊（SMAW） 焊条电弧焊是药皮焊条手工电弧焊的简称（焊条电弧焊是药皮焊条手工电弧焊的简称（SMAW, Shielded Metal Arc Welding）。是用手工操纵焊条施焊的电弧焊方法。）。是用手工操纵焊条施焊的电弧焊方法。它利用焊条与工件之间燃烧的电弧热它利用焊条与工件之间燃烧的电弧热熔化焊条端部和工件的局部，在焊条熔化焊条端部和工件的局部，在焊条端部迅速熔化的金属以细小熔滴经弧端部迅速熔化的金属以细小熔滴经弧柱过度到工件已经局部熔化的金属中，柱过度到工件

23、已经局部熔化的金属中，并与之融合一起形成熔池，随着电弧并与之融合一起形成熔池，随着电弧向前移动，熔池的液态金属逐步冷却向前移动，熔池的液态金属逐步冷却结晶而形成焊缝。焊接过程中，焊条结晶而形成焊缝。焊接过程中，焊条芯是焊接电弧的一个极，并作为填充芯是焊接电弧的一个极，并作为填充金属熔化后就成为焊缝的组成部分；金属熔化后就成为焊缝的组成部分；焊条的药皮经电弧高温分解和熔化而焊条的药皮经电弧高温分解和熔化而生成气体和熔渣，对金属熔滴和熔池生成气体和熔渣，对金属熔滴和熔池起防止大气污染的保护作用和冶金反起防止大气污染的保护作用和冶金反应作用；某些药皮加入金属粉末为焊应作用；某些药皮加入金属粉末为焊缝

24、提供附加的填充金属。缝提供附加的填充金属。29Shielded Metal Arc Welding (SMAW) The electrode holder is connected through a welding cable to one terminal of the power source and the workpiece is connected through a second cable to the other terminal of the power source. The heat of the arc causes both the core wire and th

25、e flux covering at the electrode tip to melt off as droplets. The molten metal collects in the weld pool and solidifies into the weld metal.The lighter molten flux, on the other hand, floats on the pool surface and solidifies into a slag layer at the top of the weld metal.30Shielded Metal Arc Weldin

26、g (SMAW)Protection: It provides a gaseous shield to protect the molten metal from air.Deoxidation: It provides deoxidizers and fluxing agents to deoxidize and cleanse the weld metal. The solid slag formed also protects the already solidified but still hot weld metal from oxidation.Arc Stabilization:

27、 It provides arc stabilizers to help maintain a stable arc. Arc stabilizers are compounds that decompose readily into ions in the arc. They increase the electrical conductivity of the arc and help the arc conduct the electric current more smoothly.Metal Addition: It provides alloying elements and/or

28、 metal powder to the weld pool. The former helps control the composition of the weld metal while the latter helps increase the deposition rate. Functions of Electrode Covering31焊条电弧焊（焊条电弧焊（SMAW）工艺特点工艺特点1）设备简单，操作灵活方便，适应性强，可达性好，不受场地和焊接位置的）设备简单，操作灵活方便，适应性强，可达性好，不受场地和焊接位置的限制，在焊条能达到的地方一般都能施焊，这些都是被广泛应用的重要

29、原因。限制，在焊条能达到的地方一般都能施焊，这些都是被广泛应用的重要原因。2）可焊金属广，除难熔或极易氧化的金属外，大部分工业用的金属均能焊接。）可焊金属广，除难熔或极易氧化的金属外，大部分工业用的金属均能焊接。3）待焊接头装配要求较低，但对焊工操作技术要求高，焊接质量在一定程度）待焊接头装配要求较低，但对焊工操作技术要求高，焊接质量在一定程度上取决于焊工的操作水平。上取决于焊工的操作水平。4）劳动条件差，熔敷速度慢，生产效率低。因所用焊条尺寸一般已固定，每）劳动条件差，熔敷速度慢，生产效率低。因所用焊条尺寸一般已固定，每焊完一根焊条，必须更换焊条，并残留下一截焊条头，而未被充分利用，焊后焊完

30、一根焊条，必须更换焊条，并残留下一截焊条头，而未被充分利用，焊后还需清渣等，故生产率低。还需清渣等，故生产率低。32焊条电弧焊（焊条电弧焊（SMAW） 适用范围与局限性适用范围与局限性1. 可焊工件厚度范围可焊工件厚度范围1mm以下的薄板不宜用焊条电弧焊；采用坡口多层焊的厚度虽不受限以下的薄板不宜用焊条电弧焊；采用坡口多层焊的厚度虽不受限制，但效率低，填充金属量大，经济型下降，所以一般大多用在制，但效率低，填充金属量大，经济型下降，所以一般大多用在340mm之间。之间。2. 可焊金属范围可焊金属范围能焊的金属有能焊的金属有：碳钢、低合金钢、不锈钢、耐热钢、铜、铝及其合金；：碳钢、低合金钢、不锈

31、钢、耐热钢、铜、铝及其合金；能焊但可能需预热、后热或两者兼有的金属有能焊但可能需预热、后热或两者兼有的金属有：铸铁、高强度钢、淬：铸铁、高强度钢、淬火钢等；火钢等；不能焊的金属主要有不能焊的金属主要有：低熔点金属如锌、铅、锡及其合金；难熔金属：低熔点金属如锌、铅、锡及其合金；难熔金属如钨、钼等，活性金属如钛、铌、鋯等。如钨、钼等，活性金属如钛、铌、鋯等。3. 最合适的产品结构和生产性质最合适的产品结构和生产性质结构复杂的产品，在结构上具有很多短的或不规则的、具有各种空间结构复杂的产品，在结构上具有很多短的或不规则的、具有各种空间位置及其它不易实现机械化或自动化焊接的焊缝，最宜用焊条电弧焊。位置

32、及其它不易实现机械化或自动化焊接的焊缝，最宜用焊条电弧焊。单件或小批量的焊接产品多采用焊条电弧焊。在安装或修理部门因焊单件或小批量的焊接产品多采用焊条电弧焊。在安装或修理部门因焊接位置不定，焊接工作量相对较小，也宜采用焊条电弧焊。接位置不定，焊接工作量相对较小，也宜采用焊条电弧焊。33Advantages Simple, portable, and inexpensive All-position welding Maintenance, repair, and field constructionDisadvantages Limited deposition rate Limited le

33、ngth of the electrode (about 350mm) requires electrode changing which further reduces the overall production rate Operated manually, high requirements of labor skills Poor working conditionsShielded Metal Arc Welding (SMAW)34Shielded Metal Arc Welding (SMAW)(1) Applicable thickness of the workpiece:

34、 3-40mm. (2) Area of applicationApplicable metals: carbon steels, low alloy steels, stainless steels, heat-resistant steels, copper, aluminum.Pre- and/or post-heat treatment: cast iron, high-strength steel, quenched steels, etc.Not recommended for low-melting point metals (e.g. zinc, lead, tin, etc.

35、), refractory metals (molybdenum, wolfram, etc.) and reactive metals (titanium, niobium, zirconium).35(3) Most applicable structures and productsComplicated structures: short weld, irregular weld, all types of positions difficult for automatic welding Single piece or small batch productionRepair, ma

36、intenance, etc.Shielded Metal Arc Welding (SMAW)36Gas tungsten arc welding (GTAW) Gastungsten arc welding (GTAW) is a process that melts and joins metals by heating them with an arc established between a nonconsumable tungsten electrode and the metals。 The shielding gas goes through the torch body a

37、nd is directed by a nozzle toward the weld pool to protect it from the air.Gastungsten arc welding: (a) overall process; (b) welding area enlarged37钨极气体保护焊（TIG）在惰性气体的保护下，利用钨电极与工件之间产生的电弧热熔化母材在惰性气体的保护下，利用钨电极与工件之间产生的电弧热熔化母材和填充焊丝的焊接方法称钨极惰性气体保护焊，简称和填充焊丝的焊接方法称钨极惰性气体保护焊，简称TIG焊焊（Tungsten Inert Gas Welding)或

38、或GTAW（Gas Tungsten Arc Welding）。）。 TIG焊有手工焊、半自动焊和焊有手工焊、半自动焊和自动焊三种操作方式。手工焊自动焊三种操作方式。手工焊时，焊枪的运动和焊丝的送进时，焊枪的运动和焊丝的送进均由焊工左右手同时操作；半均由焊工左右手同时操作；半自动焊时，焊枪由手工操作，自动焊时，焊枪由手工操作，焊丝由专门的送丝机构等速地焊丝由专门的送丝机构等速地自动输送；自动焊时，分别有自动输送；自动焊时，分别有行走机构、送丝机构，完成这行走机构、送丝机构，完成这两个动作。两个动作。38钨极气体保护焊（钨极气体保护焊（TIG） TIG焊的工艺特点焊的工艺特点1）焊接时使用不熔化

39、的钨电极，不存在电极熔化对弧长的影响）焊接时使用不熔化的钨电极，不存在电极熔化对弧长的影响问题，故电弧长度易于控制。需要填充金属时，可从侧面向电弧问题，故电弧长度易于控制。需要填充金属时，可从侧面向电弧送进焊丝，焊接电流不受影响。送进焊丝，焊接电流不受影响。2）焊接时，保护焊接区的是惰性气体，不需加入任何焊剂即可）焊接时，保护焊接区的是惰性气体，不需加入任何焊剂即可获得纯净的焊缝金属。因此，几乎可以焊接所有的金属。获得纯净的焊缝金属。因此，几乎可以焊接所有的金属。3）为了避免钨极被损坏和不致引起焊缝金属被钨污染，一般不）为了避免钨极被损坏和不致引起焊缝金属被钨污染，一般不用接触（短路）式引弧，

40、而采用非接触式引弧。为此，需配备一用接触（短路）式引弧，而采用非接触式引弧。为此，需配备一个引弧装置；对于普通交流个引弧装置；对于普通交流TIG焊，还需配备稳弧装置，以使焊焊，还需配备稳弧装置，以使焊接过程电弧稳定。接过程电弧稳定。4）无论使用直流电源还是交流电源，都要求具有陡降或垂直下）无论使用直流电源还是交流电源，都要求具有陡降或垂直下降（即恒流）的外特性，以减小或排除因弧长变化引起焊接电流降（即恒流）的外特性，以减小或排除因弧长变化引起焊接电流的波动。的波动。39钨极气体保护焊（钨极气体保护焊（TIG）TIG焊的三种极性焊的三种极性40钨极气体保护焊（钨极气体保护焊（TIG） 阴极雾化或

41、阴极清理作用阴极雾化或阴极清理作用TIG焊接过程中，当母材为阴极时，电弧焊接过程中，当母材为阴极时，电弧中质量较大的正离子高速向母材表面撞击，中质量较大的正离子高速向母材表面撞击，就象喷砂的作用一样，把母材表面的氧化就象喷砂的作用一样，把母材表面的氧化膜打碎并清除掉，这种现象称阴极清理作膜打碎并清除掉，这种现象称阴极清理作用，又称阴极破碎作用。如图所示为铝的用，又称阴极破碎作用。如图所示为铝的TIG焊焊缝外观示意图。焊缝周围的白边，焊焊缝外观示意图。焊缝周围的白边，就是因清洗作用把母材表面氧化膜去除的就是因清洗作用把母材表面氧化膜去除的痕迹。发生阴极清洗作用的基本条件是母痕迹。发生阴极清洗作用

42、的基本条件是母材必须是负极，正极不能发生。因此，只材必须是负极，正极不能发生。因此，只有直流反接和交流负半周期内才能有这种有直流反接和交流负半周期内才能有这种作用。此外，发生的范围是在惰性气体充作用。此外，发生的范围是在惰性气体充分包围的地方，混入空气就不发生这种作分包围的地方，混入空气就不发生这种作用。惰性气体流量不足，其作用范围就会用。惰性气体流量不足，其作用范围就会减少。减少。41 AdvantagesGastungsten arc welding is suitable for joining thin sections because of its limited heat inpu

43、ts. The feeding rate of the filler metal is somewhat independent of the welding current, thus allowing a variation in the relative amount of the fusion of the base metal and the fusion of the filler metal. Therefore, the control of dilution and energy input to the weld can be achieved without changi

44、ng the size of the weld. It can also be used to weld butt joints of thin sheets by fusion alone, that is, without the addition of filler metals or autogenous welding. Since the GTAW process is a very clean welding process, it can be used to weld reactive metals, such as titanium and zirconium, alumi

45、num, and magnesium.Gas tungsten arc welding (GTAW)42 DisadvantagesHowever, the deposition rate in GTAW is low. Excessive welding currents can cause melting of the tungsten electrode and results in brittle tungsten inclusions in the weld metal. However, by using preheated filler metals, the depositio

46、n rate can be improved. In the hot-wire GTAW process, the wire is fed into and in contact with the weld pool so that resistance heating can be obtained by passing an electric current through the wire.Gas tungsten arc welding (GTAW)43钨极气体保护焊（钨极气体保护焊（TIG） TIG焊的优点焊的优点1）在惰性气体保护下焊接，不需）在惰性气体保护下焊接，不需使用焊剂就可

47、以焊接几乎所有金使用焊剂就可以焊接几乎所有金属；特别适于焊接化学活性强和属；特别适于焊接化学活性强和形成高熔点氧化物的铝、镁及其形成高熔点氧化物的铝、镁及其合金。合金。2）焊接工艺性能好。明弧，能观）焊接工艺性能好。明弧，能观察电弧及熔池；电弧燃烧稳定，察电弧及熔池；电弧燃烧稳定，无飞溅，焊后不须去渣，焊缝成无飞溅，焊后不须去渣，焊缝成型美观；能进行全位置焊接。是型美观；能进行全位置焊接。是实现单面焊背面成形的理想焊接实现单面焊背面成形的理想焊接方法。方法。3）能进行脉冲焊接，减少焊接热）能进行脉冲焊接，减少焊接热输入，很适于薄板或对热敏感材输入，很适于薄板或对热敏感材料的焊接。料的焊接。 T

48、IG焊的缺点焊的缺点1）熔深浅，熔敷速度小，焊接生产）熔深浅，熔敷速度小，焊接生产率较低。率较低。2）钨极载流能力有限，过大焊接电）钨极载流能力有限，过大焊接电流会引起钨极熔化和蒸发，其微粒流会引起钨极熔化和蒸发，其微粒可能进入熔池，造成对焊缝金属的可能进入熔池，造成对焊缝金属的污染。污染。3）焊接时，需采取防风措施。）焊接时，需采取防风措施。4）惰性气体较贵，生产成本较高。）惰性气体较贵，生产成本较高。44钨极气体保护焊（TIG）Manual TIG手工钨极氩弧焊Automatic TIG全自动钨极氩弧焊45钨极气体保护焊（钨极气体保护焊（TIG） 适用范围适用范围1. 适焊的材料适焊的材料

49、钨极氩弧焊几乎可焊接所有的金属和合金，但因其成本较高，生产中主要用钨极氩弧焊几乎可焊接所有的金属和合金，但因其成本较高，生产中主要用于焊接铝、镁、钛、铜等有色金属及其合金，不锈钢和耐热钢。对于低熔点于焊接铝、镁、钛、铜等有色金属及其合金，不锈钢和耐热钢。对于低熔点易蒸发的金属如铅、锡、锌等因焊接操作困难，一般不用易蒸发的金属如铅、锡、锌等因焊接操作困难，一般不用TIG焊。对已镀有锡、焊。对已镀有锡、锌、铅等低熔点金属层的碳钢，焊前需去掉镀层，否则熔入焊缝金属中生成锌、铅等低熔点金属层的碳钢，焊前需去掉镀层，否则熔入焊缝金属中生成中间合金会降低接头性能。中间合金会降低接头性能。2. 适焊的焊接接

50、头和位置适焊的焊接接头和位置常规的对接、搭接、常规的对接、搭接、T形接和角接等接头，处在任何位置（即全位置）只要结形接和角接等接头，处在任何位置（即全位置）只要结构上具有可达性均能焊接。构上具有可达性均能焊接。3. 适焊的板厚与产品结构适焊的板厚与产品结构从生产率考虑以从生产率考虑以3mm以下的薄板焊接最适宜。重要厚壁结构件的根部熔透焊以下的薄板焊接最适宜。重要厚壁结构件的根部熔透焊道或其它结构窄间隙焊缝的打底焊道，为了保证焊接质量，有时采用道或其它结构窄间隙焊缝的打底焊道，为了保证焊接质量，有时采用TIG焊。焊。手工手工TIG焊宜用于结构形状较复杂的焊件和难以接近的部位或间断的短焊缝的焊宜用

51、于结构形状较复杂的焊件和难以接近的部位或间断的短焊缝的焊接；自动焊接；自动TIG焊适于焊接长焊缝，包括纵锋、环锋和曲线焊缝。焊适于焊接长焊缝，包括纵锋、环锋和曲线焊缝。46氩弧焊视频氩弧焊视频（319）47Gas metal arc welding (GMAW) Gasmetal arc welding (GMAW) is a process that melts and joins metals by heating them with an arc established between a continuously fed filler wire electrode and the me

52、tals. Shielding of the arc and the molten weld pool is often obtained by using inert gases such as argon and helium, and this is why GMAW is also called the metalinert gas (MIG) welding process. Since noninert gases, particularly CO2, are also used,GMAW seems a more appropriate name.48 Category of G

53、MAW processGas metal arc welding (GMAW)49Gas metal arc welding (GMAW)Gasmetal arc welding: (a) overall process; (b) welding area enlarged50Gas metal arc welding (GMAW) Modes of Metal TransferShallow weld,Thin workpieceIrregular weld,SpatteringDeep penetration,Stable transferShort-Circuiting Transfer

54、短路过渡Globular Transfer滴状过渡Spray Transfer喷射过渡51熔化极气体保护焊（熔化极气体保护焊（MIG）熔滴过渡形式（熔滴过渡形式（a 滴状过渡；滴状过渡；b 喷射过渡）喷射过渡）52熔化极气体保护焊（熔化极气体保护焊（MIG）The is characterized by an axial transfer of fine, discrete molten particles or drops from the consumable electrode to the workpiece at rates of several hundred per second

55、. The metal transfer is very stable, directional, and essentially free of spatter. Spray transfer is produced by welding in the DC electrode positive mode at high voltages (typically 2730V) and amperages above some critical value related to the wires diameter. The high arc energy and heat associated

56、 with the spray transfer mode limits its effectiveness for joining sheet gauge metals, but the strong directional spray (often referred to as “arc stiffness”) can be useful for welding vertically up or down or overhead, all of which are said to be “” compared to downward or “down-hand” on a horizont

57、al plane.53熔化极气体保护焊（熔化极气体保护焊（MIG）The is characterized by large globules or drops of molten metal being formed at the tip of the consumable electrode and then being released and carried to the workpiece and weld by gravity and/or arc forces. Globule formation is usually from about one per second to f

58、ive per second. The large drop size tends to make out-of-position welding difficult, as there is no directed “push” to make the drops fight gravity. is usually considerable compared to spray transfer.54熔化极气体保护焊（熔化极气体保护焊（MIG）In the which is known as a “bridging” mode, welding currents and voltages ar

59、e kept low and the slow-forming globules at the tip of the consumable electrode are periodically touched to the weld puddle to cause their release through surface tension forces.This short-circuiting occurs at rates in excess of 50 per second and is best performed using specially designed power sour

60、ces. The low currents required for this mode enable the welding of thin sections without melting through or overwelding. Out-of-position welding is facilitated by the direct transfer of the molten metal through contact. Spatter is minimized with this transfer mode.It is possible to superimpose inter