42Storage and handling

Good handling practices are required if aluminium components are to be supplied to the customer in an unmarked condition. Aluminium is a relatively soft material and is easily scored or dented by clumsy handling or the use of inappropriate lifting equipment. Over-centre edge clamps, commonly used on steels, can score plate edges and steel chains can produce scratches and dents. A solution to marking by clamps is to face the jaws with a soft material - wood or polythene blocks are excellent as...

922 Single phase DC units

Single phase DC units are rather more energy efficient than the single phase AC units as rectification of the current in the secondary circuit reduces losses due to inductance. Power demand across the phases is also more balanced than the single phase units. Although the rectifier adds to the weight the increased efficiency enables a lighter transformer to be used, giving an overall reduction in weight. The equipment cost is greater than the simple transformer AC unit but an improvement in weld...

552 Backing bars and backing strips

Although it is possible to deposit a sealing run on the reverse side of a butt weld without a back-gouge, this cannot be relied upon to give a sound, defect-free weld. Single sided joints may be welded by TIG to produce a sound root pass but the conventional (non-pulsed) MIG process often requires either permanent or temporary backing on which to deposit the MIG root pass. The purpose of the backing bar or strip is to support the root pass where conditions make the control of the bead...

225 Precipitation age hardening

Microstructures with two or more phases present possess a number of ways in which the phases can form. The geometry of the phases depends on their relative amounts, whether the minor phase is dispersed within the grains or is present on the grain boundaries and the size and shape of the phases. The phases form by a process known as precipitation, which is both time and temperature controlled and which requires a reduction in solid solubility as the temperature falls, i.e. more of the solute can...

43 Plasmaarc cutting

Plasma-arc may be used for either cutting or welding and is the most widely used thermal process for cutting of aluminium alloys in manual, mechanised or fully automated modes (Fig. 4.1). In the latter case cuts of excellent quality can be achieved in material of up to 250 mm thickness at high cutting speeds. 4.1 Fully programmable CNC plasma-jet cutting system. Courtesy of Messer Griesheim. 4.1 Fully programmable CNC plasma-jet cutting system. Courtesy of Messer Griesheim. 4.2 Schematic...

722 Wire feeders and welding torches 7221 Welding torches

The MIG process requires the filler wire to be delivered to the welding torch (Fig. 7.10) at a fixed speed and for the welding current to be transferred to the wire via a contact tip within the torch. The torch must also be equipped with a means of providing the shield gas and of enabling the welder to commence and end the welding sequence. This is generally achieved by means of a trigger on the handle of the torch. Operating the trigger initiates the shielding gas flow and the welding current...

551 The butt weld

Weld Bevel Angle

The butt weld, typical forms of which are illustrated in Fig. 5.8, is a simple and easily designed joint which uses the minimum amount of material. Figure 5.8 also includes definitions of some of the features of a weld preparation such as 'root face', 'angle of bevel' and 'included angle'. Butt welds, as illustrated in Fig. 5.5, may also be classified as full penetration or partial penetration. With the conventional fusion welding processes of TIG and MIG penetration of weld metal into the...

231 Porosity in aluminium and its alloys

Porosity is a problem confined to the weld metal. It arises from gas dissolved in the molten weld metal becoming trapped as it solidifies, thus forming bubbles in the solidified weld (Fig. 2.7). Porosity can range from being extremely fine micro-porosity, to coarse pores 3 or 4 mm in diameter. The culprit in the case of aluminium is hydrogen, which has high solubility in molten aluminium but very low solubility in the solid, as illustrated in Fig. 2.8. This shows a decrease of solubility to the...

242 Heat affected zone

As mentioned earlier, alloys in the as-cast or annealed condition may be welded without any significant loss of strength in the HAZ, the strength of the weldment matching that of the parent metal. Where the alloy has had its strength enhanced by cold work or precipitation hardening then there may be a substantial loss of strength in the HAZ. The cold worked alloys will experience a loss of strength due to recrys-tallisation in the HAZ. Recrystallisation begins to take place when the temperature...

British and ISO standards related to welding and aluminium

Listed below are all of the European and ISO standards that are related to the properties, composition and product forms of aluminium and its alloys. The list also includes design codes, welding specifications, procedure and welder approval specifications, welding guides and health and safety specifications. The list is up to date at the time of writing - May 2002 - but it should not be regarded as a definitive up-to-date listing as specifications, in particular the EN and ISO standards, are...

1021 The BS EN 288 specifications for arc welding approval

The EN series are all entitled 'Specification and Approval of Welding Procedures for Metallic Materials'. There are currently 9 parts of the EN specifications as follows Part 1 General Rules for Fusion Welding. Part 2 Welding Procedure Specification for Arc Welding. Part 3 Welding Procedure Tests for the Arc Welding of Steel. Part 4 Welding Procedure Tests for the Arc Welding of Aluminium and its Alloys. Part 5 Welding Approval by Using Approved Welding Consumables for Arc Welding. Part 6...

35 Filler metal selection

Filler metal specifications are to be found in BS 2019 Part 4, although this will be replaced in the near future by a CEN specification. The BS specification lists 11 filler metal types in the 1XXX, 3XXX, 4XXX and 5XXX series and details the delivery conditions. BS 2901 does not include any filler metals capable of being age hardened. The American Welding Society has Table 3.1 General guidance on filler metal selection Table 3.1 General guidance on filler metal selection Table 3.2 Guidance on...

234 Hot cracking

Hot cracking is a welding problem that does not occur in pure metals but may be found in certain alloy systems. It is not confined to the aluminium alloys but is also encountered in steels, nickel and copper alloys. The funda mental mechanism is the same in all of the alloy systems and is a function of how metal alloy systems solidify. As the name suggests, this is a high-temperature cracking mechanism which, because of its prevalence, is known by a number of different names - hot cracking, hot...

852Friction stir welding

The most significant process for the welding of aluminium to be developed within the last decade of the twentieth century was the friction stir process, an adaptation of the friction welding process. This process was invented at TWI in the UK in 1991 and, unlike the conventional rotary or linear motion processes, is capable of welding longitudinal seams in flat plate. Despite being such a new process friction stir welds have already been launched into space in 1999 in the form of seams in the...

223 Solid solution strengthening

Very few metals are used in the pure state, as generally the strength is insufficient for engineering purposes. To increase strength the metal is alloyed, that is mixed with other elements, the type and amount of the alloying element being carefully selected and controlled to give the desired properties. An alloy is a metallic solid formed by dissolving, in the liquid state, one or more solute metals, the alloying elements, in the bulk metal, the solvent. On cooling the alloy solidifies as a...

112Defects in arc welding

Lack Fusion

A list of weld defects and their causes is given in Table 11.1. Other defects not listed are mainly those of geometry and include misshapen and incorrectly sized welds, variable cap width and height,weld face roughness, incomplete weld fill and asymmetry of fillet welds. These are all welder-induced problems, requiring improved shop-floor discipline and or welder retraining. If the required acceptance level for the defects listed above is not contained within a relevant application standard...

1032 Asme Ix welder approval

The ASME code covers both procedure approval qualification and welder approval. Welders are divided into two categories, those who perform manual or semi-automatic MIG welding and those who operate machine or automatic welding equipment. As with EN 287 Part 2 the welder must Table 10.12 Approval related to test weld position Welding position of approval test piece 1 PB for pipes may be welded in two versions. 1 pipe rotating axis horizontal weld horizontal vertical. 2 pipe fixed axis vertical...